CDECK ID>, INFORM. H E R W I G a Monte Carlo event generator for simulating +---------------------------------------------------+ | Hadron Emission Reactions With Interfering Gluons | +---------------------------------------------------+ G. Marchesini, Dipartimento di Fisica, Universita di Milano I.G. Knowles(*), M.H. Seymour(+) and B.R. Webber, Cavendish Laboratory, Cambridge ------------------------------------------------------------------------ with Deep Inelastic Scattering and Heavy Flavour Electroproduction by G.Abbiendi(@) and L.Stanco, Dipartimento di Fisica, Universita di Padova ------------------------------------------------------------------------ and Jet Photoproduction in Lepton-Hadron Collisions by J. Chyla, Institute of Physics, Prague ------------------------------------------------------------------------ (*)present address: Dept. of Physics & Astronomy, University of Glasgow ------------------------------------------------------------------------ (+)present address: Theory Division, CERN ------------------------------------------------------------------------ (@)present address: DESY, Hamburg ------------------------------------------------------------------------ Version 5.9 - 22nd July 1996 ------------------------------------------------------------------------ Main reference: G.Marchesini, B.R.Webber, G.Abbiendi, I.G.Knowles, M.H.Seymour, and L.Stanco, Computer Physics Communications 67 (1992) 465. ------------------------------------------------------------------------ Please send e-mail about this program to one of the authors at the following addresses: Decnet : 19616::webber, vxdesy::abbiendi, 19800::knowles Internet : webber@hep.phy.cam.ac.uk, knowles@v2.ph.gla.ac.uk, seymour@surya11.cern.ch, abbiendi@vxdesy.desy.de ------------------------------------------------------------------------ ****** CONTENTS ****** 1. INTRODUCTION 2. NEW FEATURES OF THIS VERSION 3. FEATURES NOT YET INCLUDED 4. PROGRAM STRUCTURE 5. BEAMS AND PROCESSES 6. INPUT PARAMETERS 7. COMMON BLOCK FILE 8. FORM FACTOR FILE 9. EVENT DATA 10. STATUS CODES 11. EVENT WEIGHTS 12. HEAVY FLAVOUR DECAYS 13. SPACE-TIME STRUCTURE OF EVENTS 14. COLOUR REARRANGEMENT MODEL 15. QCD HARD SUBPROCESSES 16. DIRECT PHOTON SUBPROCESSES 17. QCD HIGGS PLUS JET SUBPROCESSES 18. ELECTROWEAK SUBPROCESSES 19. INCLUDING NEW SUBPROCESSES 20. ERROR CONDITIONS 21. SAMPLE OUTPUT 22. GUIDE TO SAMPLE OUTPUT ------------------------------------------------------------------------ ****** 1. INTRODUCTION ****** HERWIG is a general-purpose event generator for high energy hadronic processes, with particular emphasis on the detailed simulation of QCD parton showers. The program has the following special features: * Simulation of any combination of hard lepton, hadron or photon scattering and soft hadron-hadron collisions in one package. * Colour coherence of partons (initial and final) in hard subprocesses * Heavy flavour hadron production and decay with QCD coherence effects * QCD jet evolution with soft gluon interference via angular ordering * Backward evolution of initial-state partons including interference * Azimuthal correlations within and between jets due to interference * Azimuthal correlations within jets due to gluon polarization * Cluster hadronization of jets via non-perturbative gluon splitting * A complete space-time picture from parton showers to hadronic decays * A colour rearrangement model based on an events space-time structure * A similar cluster model for soft and underlying hadronic events Further details may be found in the references cited above and at the end of this section, and in comments distributed throughout the code. The program operates by setting up parameters in common blocks and then calling a sequence of subroutines to generate an event. Para- meters not set in the main program HWIGPR are set to default values in the main initialisation routine HWIGIN. To generate events the user must first set up the beam particle names PART1, PART2 (type CHARACTER*8) in the common block /HWBEAM/, and the beam momenta PBEAM1, PBEAM2 (in GeV/c), a process code IPROC and the number of events required MAXEV in /HWPROC/. See section 5 for beams and processes available. All analysis of generated events (histogramming, etc.) should be performed by the user-provided routines HWABEG (to initialise), HWANAL (to analyse an event) and HWAEND (to terminate). At present HWANAL writes event information and stable particle data on unit LWEVT defined in HWIGIN (or simply returns if LWEVT=0). See HWANAL for details of event information written. Note that HWANAL should always begin with the line IF (IERROR.NE.0) RETURN to prevent it being executed for incomplete events. A detailed event summary is printed out for the first MAXPR events (default MAXPR=1). Set IPRINT=2 to list the particle identity codes and (simplified) particle decay schemes used in the program. The programming language is standard Fortran 77 as far as possible. However, the following may require modification for running on computers other than Vax's: * Most common blocks are inserted by INCLUDE 'HERWIG59.INC' Vax Fortran statements (see below for contents of HERWIG59.INC) * Subroutine HWUTIM (returning CPU time left) is machine dependent. The principal references are: G.Marchesini and B.R.Webber, Nucl. Phys. B310 (1988) 461; I.G. Knowles, Nucl. Phys. B310 (1988) 571; S.Catani, G.Marchesini and B.R.Webber, Nucl. Phys. B349 (1991) 635; G.Abbiendi and L.Stanco, Comp.Phys.Comm. 66 (1991) 16, Zeit. Phys. C51 (1991) 81; M.H.Seymour, Zeit. Phys. C56 (1992) 161. Some additional relevant references are: A.Bassetto, M.Ciafaloni and G.Marchesini, Phys. Rep. 100 (1983) 201; G. Marchesini and B.R. Webber, Nucl. Phys. B238 (1984) 1; Phys. Rev. D38 (1988) 3419; B. R. Webber, Nucl. Phys. B238 (1984) 492; Ann. Rev. Nucl. Part. Sci. 36 (1986) 253; I.G. Knowles, Nucl. Phys. B304 (1988) 794; Computer Phys. Comm. 58 (1990) 271. ------------------------------------------------------------------------ ****** 2. NEW FEATURES OF THIS VERSION ****** * The common block file HERWIG59.INC has been significantly rearranged and tidied up. * Many new hadrons have been added. All S & P wave mesons are present including the 1^P_0 & 3^P_1 states and many new, excited B^**, B_c & quarkonium states. Also all D wave kaons and some `light' I=3 states [pi_2, rho(1700) & rho_3]. All the baryons (singlet/octet/decuplet) containing up to one heavy (c,b) quark are included. --- Consequently the default parameters require retuning --- * New 8-character particle names have been introduced and the revised 7 digit PDG numbering scheme, as advocated in the LEP2 report, has been adopted. * The layout of HWUDAT has been altered to make it easier to identify and modify particle propeties. Three new arrays have been introduced RLTIM, RSPIN & IFLAV. These are: the particle's lifetime (ps), spin, and a code which specifies the flavour content of each hadron - used (in HWURES) to create sets of iso-flavour hadrons for cluster decay. Using the standard numbering of quark flavours the convention is: mesons: n_q n_qbar Eg. pi^+: 21, pi^-: 12 baryons: +/-n_q1 n_q2 n_q3 Eg. Xi^0: 332, Xi^0bar: -332 etc. (-ve for antibaryons; digits in decreasing order) Light, neutral mesons are identified as: 11 if I=1: pi^0,rho^0,... 33 if I=0: eta, eta'.. etc. Some parts of the program have been automated so that it is possible for the user to add new particles by specifying their properties via the arrays in /HWPROP/ & /HWUNAM/ and increasing NRES appropriately: this should be done before a call to HWUINC. As an example following lines add an isoscalar, spin pi state 'STAN' and a (very light) stable toponium state 'BEER' with the decay mode: STAN ---> BEER+BEER+BEER. NRES=NRES+1 RNAME(NRES)='STAN ' IDPDG(NRES)=666 IFLAV(NRES)=11 ICHRG(NRES)=0. RMASS(NRES)=0.5 RLTIM(NRES)=1.000D-10 RSPIN(NRES)=3.142 NRES=NRES+1 RNAME(NRES)='BEER ' IDPDG(NRES)=66 IFLAV(NRES)=66 ICHRG(NRES)=0. RMASS(NRES)=0.1 RLTIM(NRES)=1.000D+30 RSPIN(NRES)=0.0 CALL HWMODK(666,1.D0,0,66,66,66,0,0) * The mixing angles of all the light, I=0 mesons can now be set using: ETAMIX: eta <-> eta' F0MIX: f_0(1300) <-> f_0(980) PHIMIX: omega <-> phi, F1MIX: f_1(1285) <-> f_1(1510) H1MIX: h_1(1170) <-> h_1(1380) F2MIX: f_2 <-> f_2' * Using the logical arrays VTOCDK & VTORDK the production of specified particles can be stopped in both cluster decays and via the decay of other unstable resonances. * A priori weights for the relative production rates in cluster decays of mesons and baryons differing only via their S & L quantum numbers can be supplied using SNGWT & DECWT for singlet (i.e. Lambda-like) & decuplet baryons and REPWT for mesons. The old VECWT now corresponds to REPWT(0,1,0) and TENWT to REPWT(0,2,0). * The default masses of the c and b quarks have been lowered to 1.55 & 4.95 repectively: this corresponds to the mass of the lightest meson minus the u/d quark mass. This increases the number of heavy mesons, and hence total multiplicities, and slightly softens their momentum spectrum. The rate of photoproduced charm states increases and B-pi momentum correlations become smoother. * The resonance decay tables supplied in the program have been largely revised. Measured/expected modes with branching fraction at or above 1 per mille are given, including 4 & 5 body decays. To print the new tables call HWUDPR. * The arrays FBTM, FTOP & FHVY which stored the branching fractions of the bottom, top & heavier quarks' `partonic' decays are now nolonger used. Such decays are specified in the same way as all other decay modes: this permits different decays to be given to individual heavy hadrons. Partonic decays of charm hadrons and quarkonium states are also now supported. The products' order in a partonic decay mode is significant. For example if the decay is: Q --> W+q --> (f+fbar')+q, occuring inside a Q-sbar hadron the required ordering is: Q+sbar --->(f+fbar')+(q+sbar) or (q+fbar')+(f+sbar) `colour rearranged' In both cases the (V-A)^2 ME^2 is proportional to: p_0.p_2 * p_1*p_3 * The structure of the program has been altered so that secondary hard subrocess and subsequent fragmentation associated with each partonic heavy hadron decay appear separately. Thus pre-hadronization t quark decays are treated individually as are any subsequent bottom hadron partonic decays. * Additionally decays of heavy hadrons to exclusive non-partonic final states are supported. No check against double counting from partonic modes is included. However this isn't expected to be a major problem for the semi-leptonic and 2-body hadronic modes supplied. * An array NME has been introduced to enable a possible matrix element to be specified for each decay mode. NME = 0 Isotropic decay 100 Free particle (V-A)*(V-A): p_0.p_2 * p_1.p_3 101 Bound quark (V-A)*(V-A): p_0.p_2 * p_1*[p_3 - xs*p_0] xs = m_Q/M_0 - spectator quark momentum fraction 130 Ore & Powell ortho-positronium ME^2: onium --> gg+g/gamma. The list of matrix elements presently supported is modest, users are urged to contact an author to have other MEs implimentated. * The decay tables can be written to/read from a file by using HWIODK, adopting the format advocated in the LEP2 report. In addition to the PDG numbering of particles the HERWIG numbers or character names can be used. This permits easy alteration of the decay tables. In HWUINC a call is made to HWUDKS which sets up HERWIGs internal pointers and performs some basic checks of the decay tables. Each decay mode must conserve charge and be kinematically allowed and not contain vetoed decay products. The sum of a particles branching ratios is set to 1. Also a warning is printed if an antiparticle does not have all the charge conjugate decays modes of the particle. * HWMODK enables changes to the decay tables to be made by alterating/ adding single decay modes including on an event by event basis. This can be done before HWUINC, in which case when altering the BR and/or ME code of an existing mode a warning is given of a duplicate second mode which supercedes the first. BRs set below 10^-6 are eliminated, whilst if one mode is within 10^-6 of 1 all other modes are removed. Note that some forethought is required if the BRs of 2 modes of the same particle are changed since the operation of rescaling to 1 the BR sum causes a non-commutativity in the order of the calls. * Production vertex information is now made available, using VHEP, for all partons, clusters and final state particles: set PRVTX=.TRUE. to print them. The vertices of partons and clusters are given wrt local coordinates associated with their individual hard sub-process. * All partonic and resonace rest frame lifetimes are generated with an exponential distribution: exp(-t/)/. The average lifetime, , is given in terms of the particles mass, width and virtuality by: hbar.sqrt(q^2) (q^2) = ----------------------------- \/(q^2-M^2)^2 + (Gamma.q^2/M)^2 = hbar/Gamma for an on-shell particle ~ hbar.q/(q^2-M^2) a highly virtual particle For partons an effective width = sqrt(VMIN2), to act as a cut-off on lifetimes, is introduced. * The space-time picture for cluster formation and splitting is partly ad hoc and partly string inspired - no physics depends upon it. * All particles with lifetimes greater than PLTCUT are set stable. * If PIPSMR=.TRUE. the primary interaction point's spatial position is is smeared according to the triple Gaussian in HWRPIP: this position is assigned to the CMF track. * If MAXDKL=.TRUE. then each putative decay is tested in HWDXLM to see that it occurs within a specified volume (cylinder/sphere for IOPDKL =1/2): if not it is set stable. * If MIXING=.TRUE. then B^0_d,s mesons are allowed to oscillate: XMIX and YMIX contain Delta-M/Gamma and Delta-gamma/2*Gamma respectively. A new particle, ISTHEP=200, is introduced giving the flavour of the neutral B meson at production in addition to the `decaying' track. * A multiple intra & inter-jet colour rearrangement model is available for CLRECO=.TRUE. The q-qbar pairings in two non-adjacent clusters are interchanged with probability PRECO if the distances between the production vertices of both q-qbar pairs when added in quadrature is reduced. EXAG can be used to artificially scale the lifetimes of any weak bosons. * A number of bugs have been corrected: in HWEPRO for weighted events; in HWSBRN affecting the reconstruction of the photon beam remnant; and in HWHEPG stopping event generation. Plus minor modifications to HWBGEN; in the use of HWHIGM by HWHIGJ; and small changes in HWHDIS & HWHEGG. * A significant bug in HWDHQK, affecting top quark decays, was present in version 5.8 ONLY. The scale of the top decay had been set to the b-quark mass, stopping gluon radiation from the b and restricting that from the W decay products to have transverse momentum less than the b mass. The scales are now correctly set for top decays. * Improved efficiency of photon generation in HWEGAM. * New hard sub-process have been added: - Compton scattering, gamma + q --> gamma + q, IPROC=5300. - Two-to-two parton scattering via exchange of a colour singlet IPROC=2400 Mueller-Tang pomeron: the fixed alpha_s and omega_0 are given by ASFIXD and OMEGA0 respectively. IPROC=2450 photon exchange, for like flavour qqbar pairs including the t-channel component of the interference with q-qbar -> q-qbar. - Drell-Yan has been extended to the production of all fermion pairs IPROC=1399; 1300 gives all quark flavours 1300+IQ a specific quark flavour, 1350 all leptons (including neutrinos) 1350+IL a specific lepton flavour. The s-channel component of the interference with like flavour q-qbar scattering is included here. - Z+jet production is included as IPROC=2150 (HWHW1J becomes HWHV1J) * Running coupling now used for prompt J/PSI production in DIS. * The phase-space limits for the momentum fraction of incoming photons in the Weizsacker-Williams approximation is now set by the variables YWWMIN & YWWMAX, allowing different ranges for the tagged and untagged photons in two-photon DIS. * Interfaced to the Schuler-Sjostrand parton distribution functions, version 2. These appear as PDFLIB sets with author group 'SaSph', but are actually implemented via a call to their SASGAM code. The value in MODPDF specifices the set (1-4 for 1D [recommended set],1M, 2D,2M), whether the Bethe-Heitler process is used for heavy flavours (add 10), whether the P^2-dependence is included (add 20), and which of their P^2 models is used (add 100 times their IP2 parameter). * New variables ANOMSC(1 or 2,IBEAM) record the evolution scale and Pt at which an anomalous (gamma* --> q+qbar) splitting was generated in the backward evolution of beam IBEAM. set 0 if no such splitting was generated. This is implemented in HWBGEN and HWSBRN. * In preparation for multiple interactions, several routines have been added or modified. New are: HWHREM for identifying and cleaning up the beam remnants; HWHSCT to administer the extra scatters. Minor modifications to: HWBGEN & HWSBRN, don't report energy conservation errors when ISLENT = -1; HWSSPC, improved approximation for remnant mass at high energies; and HWUPCM, improved safety against negative square roots. * Photon Initial State Radiation in e+e- annihilation events allowed. TMNISR sets the minimum s-hat/s value, ZMXISR sets the (arbitrary) separation between unresolved and resolved emission; using ZMXISR=0 switches off photon ISR. * Numerical integral in HWBDED now done analytically removing the need to reintegrate for each new energy; in principle allowing use in 5- jet WW events, but this is not yet implemented. * New phase-space variable WHMIN added. This sets the minimum allowed hadronic mass and affects photoproduction reactions (gamma-hadron & gamma-gamma) and DIS. In lepton-hadron DIS it is largely irrelevant since there is already a cut on Bjorken y which at fixed s is almost the same but for lepton-gamma DIS it makes a big difference. * A new treatment of running Higgs width and non-resonant diagrams, as suggested in M.H. Seymour, Phys. Lett. B354 (1995) 409. Selected by setting IOPHIG=2 or 3 (default); previous options 2 and 3 have been withdrawn. Note that including the non-resonant diagrams changes the meaning of what is generated: IOPHIG = 0 or 1, gives the s-channel diagram, an unphysical choice of part of the amplitude; IOPHIG = 2 or 3, gives the I=0 & J=0 part of the excess over the cross section expected for a zero mass Higgs boson, a physical choice of part of the cross section. The inclusion of non-resonant diagrams causes the cross section to increase below and decrease above resonance. * New treatment of the splitting in two of clusters containing hadron (or photon) remnants. Previous versions gave the 2 fragments a mass spectrum typical of soft processes: dn/dm**2 = Gaussian. In the new version the child containing the remnant is treated as before but the other cluster, containing a perturbative parton, is treated as a normal clusters: dn/dm = m**psplt. IOPREM controls this behaviour: 0 = old version, 1 = new (default). * Direct gamma+gamma* -> q+qbar is included in the hard correction for lepton-gamma DIS; plus minor bug fixed in HWBDIS. * The dummy routine IUCOMP has been removed, this avoids errors when the program is linked to CERNLIB. * It has been noticed that differences in the way quark masses are treated in different processes can cause inconsistencies between different ways of generating the same process. The most noticeable example is in direct photoproduction, where one can use process 9130 or 5000. See the note at the end of Section 5 of the documentation for more information on the strategies used in different processes. Version 5.1 of HERWIG was described in detail in Computer Physics Communications 67 (1992) 465. For completeness we list here also the main new features added in versions 5.2 - 5.7. In version 5.2: * New e+e- processes: - two photon processes, IPROC = 500+ID where ID=0-10 is the same as in Higgs processes for qqbar, llbar, and W+W-. The phase space is controlled by EMMIN,EMMAX for the CMF mass, PTMIN,PTMAX for the transverse momentum of the CMF in the lab, and CTMAX for the CMF angle of the outgoing particles. - photon-W fusion, IPROC = 550+ID where ID=0-9 is the same as in Higgs processes, except that ID=1 or 2 both give the sum of dubar and udbar etc. The phase space is controlled by EMMIN,EMMAX only. The full 2-->3 matrix elements for photon e-->f f'bar nu are used, so the cross section for real W production is correctly included. - ZZ pair production, IPROC=250 is treated just like WW production, and is based on the program kindly supplied by Zoltan Kunszt. * New ep processes: - the phase space for BGF is now controlled by EMMIN,EMMAX as above. The default values are 0 and RootS respectively, corresponding to the behaviour of version 5.1 - J/psi production from BGF, IPROC = 9104 is now available. - W W fusion to Higgs is now available in ep, IPROC = 9500+ID. * IPROC = 1600+ID now gives the sum of gluon fusion and q qbar fusion. This is especially important in e+e- if tan(beta) is large, when it is dominated by e+e- --> e+e- gamma gamma --> e+e- b bbar H. * Users can now force Z --> b bbar decays, with MODBOS(i)=7 (for a complete list see section 18). For example, IPROC=250, MODBOS(1)=7, MODBOS(2)=0 gives ZZ production with one Z decaying to b bbar. * All Higgs vertices now include an enhancement factor to account for non-SM couplings. ENHANC(ID), where ID=1-11 is the same as for Higgs production, holds the ratio of the AMPLITUDE for the given vertex to that of the SM. This of course only simulates the chargeless scalars of any extended model, and not the pseudoscalars or charged Higgses. * The heavy quark content of the photon now uses the corrections to the Drees-Grassie distribution functions for light quarks, recently calculated by C.S.Kim et al. (see M.Drees & C.S.Kim, DESY 91-039 and C.S.Kim, Durham preprint DTP/91/16). * A new structure function set, Owens1.1, similar to Duke+Owens1, but fitted to new data (Preprint FSU-HEP-910606) is available via NSTRU=5, and is now the default structure function set. In version 5.3: * O(alpha-s) jet production in ep processes has been included (IPROC= 9200 etc), with Q**2 range controlled by Q2MIN, Q2MAX and minimum jet transverse momentum (in the hard subprocess c.m. frame) set by PTMIN. The new subroutines were written by Sebastian Brandis and we are grateful to him for permission to use his code. * Minor bugs have been fixed in the backward evolution of quarks into photons, hadronic processes in e+e-, remnant hadronization in ep, and in the generation of weighted events (ie. with NOWGT=.FALSE.). In version 5.4: * A correction to hard gluon emission in e+e- events has been added and is now the default process. This uses the O(alpha-s) matrix element to add events in the `back-to-back' region of phase-space corresponding to a quark-antiquark pair recoiling from a very hard gluon. Although this is asymptotically negligible, and cannot be produced within the shower itself, it has a sizeable effect at LEP energies. As a result, the default parameters have been retuned, and show a marked improvement in agreement with OPAL data for event shapes sensitive to three-jet configurations (J.W. Gary, private communication). The uncorrected process has been retained for comparative purposes and is available as IPROC=120+IQ. * Photons are now included in time-like parton showering. The infra- red cutoff is VPCUT, which defaults to SQRT(S) corresponding to no emission. Agreement with LEP data is satisfactory if used together with the matrix element correction to produce photons in the back- to-back region. The results are insensitive to VPCUT variations in the range 0.1-1.0 GeV. * W decay correlations and width are now correctly included in W+jet production (previous versions used unpolarized, on-shell approx.). * An inconsistency in the argument used for alpha_s in the branching g -> q qbar has been removed. The change is a non-leading correction but leads to slightly more quarks in gluon jets. * A new parameter B1LIM has been introduced for B cluster hadroniz- ation. If MCL is the B cluster mass and MTH the threshold for its decay into 2 hadrons, the probability of its decay into a single B hadron is: 1 if MCL(1+B1LIM)*MTH, with a linear interpolation i.e. 1-(MCL-MTH)/(B1LIM*MTH) if MTH0 gives a harder B spectrum. * B decays can now be performed by the EURODEC or CLEO Monte Carlo packages. The new variable BDECAY controls which package is used: 'HERW' for HERWIG; 'EURO' for EURODEC; 'CLEO' for CLEO. The EURODEC package can be obtained from the CERN library. The CLEO package is available by kind permission of the CLEO collaboration, and can be obtained from Luca Stanco at the address given above. In version 5.5: * The Sudakov form factors can now be calculated using the one-loop or two-loop alpha_s, according to the variable SUDORD (DEFAULT=1). The parton showering still incorporates the two-loop alpha_s in either case but if SUDORD=1 this is done using the veto algorithm, whereas if SUDORD=2 no vetoes are used in the final-state evolution. This means that the relative weight of any shower configuration can be calculated in a closed form, and hence that showers can be `forced'. For example, a package of routines should be available soon for forcing jets to contain photons, which will therefore drastically improve the efficiency of photon FSR studies. To next-to-leading order the two possibilities SUDORD=1 or 2 should be identical, but they differ at beyond-NLO, so some results may change a little. Previous versions were equivalent to SUDORD=1. * Alpha_em is now multiplied by the factor ALPFAC (DEFAULT=1) for all quark-photon vertices in jets, and in the `dead zone' in e+e-. This is a cheap way of improving the efficiency of photon FSR studies, which should not be needed once photon forcing is available. Note that results at small ycut become sensitive to ALPFAC above about 5. * A new parameter CLPOW (DEFAULT=2) is available in the cluster hadro- nization model. A cluster of mass MCL made of quarks of mass M1,M2 is split into lighter clusters before decaying if MCL**CLPOW > CLMAX**CLPOW + (M1+M2)**CLPOW Thus the previous value was CLPOW=2, like the new default. Smaller values will increase the yield of heavier clusters (and hence of baryons) for heavy quarks, without affecting light quarks much. For example, the default value gives no b-baryons (for the default value of CLMAX) whereas CLPOW=1.0 makes b-baryons/b-hadrons about 1/4. * The event record has been modified to retain entries for all partons before hadronization (with status ISTHEP=2). During hadronization, the gluons are split into quark-antiquark, while other partons are copied to a location (indicated by JDAHEP(1,*)) where their momenta may be shifted slightly, to conserve momentum, during heavy cluster splitting. Previously the original momenta were shifted, so momentum appeared not to be conserved at the parton level. * Minor improvements have been made to: NLO correction to Higgs decays to qqbar; pt spectra of outgoing electrons in two-photon processes; quark-mass effects in gamma-W fusion; WW spectrum below threshold in e+e-; t-bbar spectrum in W Drell-Yan (IPROC=1406). * Bugs preventing the use of Sudakov form factor tables from disk and gluon-> diquarks splitting option under some circumstances, together with other minor bugs and machine-dependences, have been fixed. In version 5.6: * Decays of very heavy quarks (top and higher generations) can occur either before or after hadronization. At present all top quarks will decay before/after hadronizing if the top mass is greater/less than 130 GeV. This can be changed in subroutine HWDTOP. All higher (>3) generations now decay before hadronization. Note that the new state- ment CALL HWDHQK must appear in the main program between the calls to HWBGEN and HWCFOR to carry out any decays before hadronization. * Bugs in the subroutine HWHDOA for O(alpha_s) jet production in DIS have been corrected by J. Chyla, who has also extended this process into the photoproduction region. If Q2MIN.LT.2D-6 (the new default), the kinematic lower limit on Q**2 is computed and used. New options IPROC=9250 to 9277 use various approximations to the neutral-current matrix element, as specified in the Table below. * The photoproduction processes have also been extended from the original heavy quark production program, to include all quark pair production (IPROC=9100-9106) and QCD Compton (IPROC=9110-9122), as well as the sum of the two (IPROC=9130). The possible flavours for the 9100,9110 and 9130 processes are limited by the input parameters IFLMIN and IFLMAX (defaults are 1 and 3, i.e. only u,d,s flavours). The corresponding Charged Current processes are now provided via the IPROC=9140-9144 codes. * All the DIS processes IPROC=9000-9599 are now available in e+e- as well as lepton-hadron collisions. The program generates a photon from the second beam (only) in Weizsacker-Williams approximation and uses Drees-Grassie structure functions for DIS on the photon. * Pointlike photon-hadron scattering to produce QCD jets is available as IPROC=5000. This is suitable for fixed-target photoproduction, provided events are generated in a frame in which the target has high momentum, and then boosted back to the lab. IPROC=5000+IQ gen- erates only those processes involving quark flavour IQ, using exact kinematics and light-cone momentum fraction. In both cases, after event generation the hard subprocess code IHPRO is set to 51,52 or 53 for photon+q->g+q, photon+qbar->g+qbar, or photon+g->q+qbar. * The default limits on Q**2 in DIS processes (Q2MIN,Q2MAX) have been set very small/large (0.0, 1.D10) and are reset to the kinematic limits unless changed by the user. This means the default Q2MIN is not suitable for simple NC DIS (IPROC=9000 etc), but is appropriate for jet and heavy quark photoproduction. * A new parameter NMXJET, the maximum number of outgoing partons in a hard subprocess (default 200) has been introduced in the common block file HERWIG56.INC. * For technical reasons, some HERWIG status codes ISTHEP between 153 and 165 have changed their meanings. See the Table in sect.10 below. * Bugs in the hadronization of diquark-antidiquark clusters have been fixed. Any such clusters with masses below threshold for decay into baryon-antibaryon are shifted to the threshold via a transfer of 4- momentum to a neighbouring cluster. * A bug in the default pion structure function (no gluons) is fixed. In version 5.7: - ELECTRO-WEAK COUPLINGS: New arrays QFCH(16), VFCH(16,2), AFCH(16,2) and VCKM(3,3) have been set up for couplings and CKM matrix. See the documentation file or HWIGIN for conventions. Note that universality is not assumed, so lepton axial couplings may differ for example; this is primarily to cover Z' possibilities, see below. The variable SCABI=sin^2 theta_Cabibbo is however also retained for the present. - A Z' has been introduced with PDG code 32, HERWIG identifier 202, default mass 500 GeV, width GAMZP (default 5 GeV) and name 'Z0PR'. It is invoked by setting ZPRIME=.TRUE. (default .FALSE.). - POLARISATION: incoming lepton and antilepton beam polarisations are now specified by setting two new vectors EPOLN(3) and PPOLN(3): component 3 is longitudinal and 1,2 transverse. Transverse only occurs in e+e- routines; recall that two transverse 'measurements' are needed to see an effect so it should not arise elsewhere. Note that in DIS processes you have to set either EPOLN if it is a lepton or (exclusive) PPOLN if an antilepton. Polarisation effects are now included in e+e- 2/3 jet production and Bjorken process, together with DIS processes apart from J/psi production. - NEW SUBPROCESSES: 2200 QCD direct photon pair production (inc. g+g->gamma+gamma) 5100+IQ Point-like photon/QCD heavy flavour pair production 5200+IQ Point-like photon/QCD heavy flavour single excitation The latter two replace 5000+IQ, while 5000 remains as before (ie a sum over all processes and flavours with simplified kinematics) - The kinematic reconstruction of DIS processes can now take place in the Breit frame, if BREIT=.TRUE. (the default value). Previous versions used the lab frame. Although the reconstruction is fully invariant under Lorentz boosts along the incoming hadron's direction, it is not under transverse boosts, so there should be some difference between the two frames. The boost is not performed for very small Q^2 (<10^-4) to avoid numerical instabilities, but the two frames are in any case equivalent for such small Q^2. - A new parameter PRSOF to produce an underlying event in only a fraction PRSOF of events (default=1.0). IPROC=19000 etc are thus equivalent to PRSOF=0. - Non-diffractive hadronic minimum bias events (IPROC=8000) can now be generated for a wider variety of beams (P,PBAR,PI+/-,K+/-,E+/-,MU+/-,GAMA on target P; also P and PBAR or leptons on target N). The event weight (previously set to 1.0 for this process) is the estimated cross section based on the parametrizations of Donnachie and Landshoff, CERN-TH.6635/92. The non-diffractive cross section is assumed to be 70% of the total. For lepton beams a photon is first generated using the effective photon approximation (see below) and then the on-shell photon cross section is used. - A bug has been fixed in HWBRAN and HWSBRN (present in versions 5.1 to 5.6) that led to too much transverse momentum being developed by the parton showers in hadron-hadron collisions. All radiation with pt greater than the hard process scale is now vetoed. In the case of initial-state radiation, this affects all events, while for final-state radiation it only affects those in which the two jets have a rapidity difference of more than about 3.4. - When SUDORD=2, no veto is needed for gluon splitting to quarks. This means that no vetoes are needed for final state showering, except for the previously-mentioned transverse momentum cut. The removal of vetoes allows preselection of the flavours that a jet will contain, giving a huge increase in the efficiency of rare process simulation. A package is already available to simulate heavy flavour production inside jets, and the equivalent for photons should soon be available. - Parameter BTCLM is now available to users to adjust the mass parameter in remnant formation. Its default value, 1.0, is identical to previous versions. - There is a new switch CLDIR for cluster decays. CLDIR=0 is the same as previous versions, while CLDIR=1 (the default) means that a cluster that contains a `perturbative' quark, ie one coming from the perturbative stage of the event (the hard process or perturbative gluon splitting) `remembers' its direction: when the cluster decays, the hadron carrying its flavour continues in the same direction (in the cluster c.m. frame) as the quark. This considerably hardens the spectrum of heavy hadrons, particularly of c- and b-flavoured hadrons. It also introduces a tendency for baryon-antibaryon pairs preferentially to align themselves with the event axis (the `TPC/2gamma string effect'). - The functionality of the routine HWUINE has now been split between it and a new routine, HWUFNE. A call to the latter MUST be inserted into the users main program, between the calls to HWMEVT and HWANAL. A check is built in to version 5.7 to prevent execution if this change is not made. See the documentation file for an example main program. We should also take this opportunity to remind users that the analysis routine HWANAL should begin with the line IF (IERROR.NE.0) RETURN since if an event is cancelled, each of the routines is still called in turn until reaching the end of the main loop. - If the new flag USECMF is .TRUE. (the default), events are boosted to their centre-of-mass frame before processing if necessary, and boosted back afterwards. This second boost is performed by the new routine HWUFNE, so it is essential that this is inserted in the correct place, as described above. - In hadronic processes with lepton beams (eg photoproduction in ep), the lepton->lepton+photon vertex now uses the full tranverse-momentum- dependent splitting function, with exact light-cone kinematics (i.e. the Equivalent Photon instead of the Weizsacker-Williams approximation). This means that the photon-hadron collision has a transverse momentum in the lepton-hadron frame, and must be boosted to a frame where it has no transverse momentum. Thus the cmf boost described above is always used in these processes, regardless of the value of USECMF. The correct lower energy cut-off appropriate to the hadronic process is applied to the photon, rather than the fixed cut of 5 GeV that was used in previous versions. The Q**2 of the photon is generated within the kinematically allowed limits, or the user-defined limits Q2WWMN and Q2WWMX (defaults 0 and 4) whichever is more restrictive. The momentum fraction is generated within the kinematic limits or between YBMIN and YBMAX (defaults 0 and 1). - Point-like photon processes (IPROC=5***) are now also available with lepton beams, using the Equivalent Photon Approximation. - Several minor improvements have been made to the O(as) processes in DIS (IPROC=91**): - A sign error has been corrected that led to the incorrect sign for the lepton-jet azimuthal correlation in QCD Compton processes. - An additional cut on the phase-space generation has been provided: the Bjorken-y variable (=Q^2/xs) is limited to range [YBMIN,YBMAX]. - BGSHAT=.FALSE. is now the default. - J/Psi production (IPROC=9107) now uses the EPA instead of the WWA, with the same phase-space cuts as hadronic processes with lepton beams, see above. - Many bugs have been fixed in the other O(as) process routines, HWHDOA and HWHDOM, ie for IPROC=92**. However, this process is no longer supported, and is only retained for comparative purposes. It will be withdrawn completely at the next version release. - An interface is now provided to Mark Gibbs' HERBVI package for baryon- number violation, and other multi-W production processes, IPROC=7***. - Minor bug fixes in HWHDIS, HWHEGW and HWHIGW and minor improvements in HWHHVY, HWHPHO, HWHQCD and HWHWEX hard process routines. - New fictional e+e- processes: e+e- -> gluon+gluon(+gluon), IPROC=107 & 127, treated just like e+e- -> quark+antiquark, summed over light quark flavours, for direct comparisons between quark and gluon jets. - New logical variable PRNDEC (default=.TRUE. unless NMXHEP>9999) causes track numbers in event listings to be printed in hexadecimal if.FALSE. This is necessary for very large events such as those generated by the HERBVI package (see above). - PDFLIB structure functions can now be used for the photon as well as nucleons. The new variable MODPHO acts just like MODPDF. PDFLIB calls have also been updated to allow for structure function sets with flavour-asymmetric sea contributions. - A logical inconsistency has been fixed in the decays of clusters to eta or eta' - previously all mixing was neglected, leading to double- counting and a significant over-estimate of the number of each. The new variable ETAMIX gives the eta_8/eta_0 mixing angle in degrees (default = -20). Rates are not very sensitive to its exact value, as the eta'/eta suppression is dominated by mass effects in the cluster model. - The maximum weight is now always printed in full precision (needed to be sure of generating the same events in repeated runs). - New constants: GEV2NB=389385 ALPHEM(1)=1./137(.03599) for Q^2=0. ALPHEM(2)=1./128 for Q^2~M_W^2 are introduced in various cross section formulae, and G_Fermi is eliminated. - The default top quark mass was increased to 150 GeV. In version 5.8 * A hard matrix element correction has been introduced in DIS (IPROC = 90**). This is switched on and off by the logical variable HARDME (default = .TRUE.). The method is essentially identical to the e+e- correction, generating first order matrix-element events in a phase-space region complementary to that of the parton shower. The e+e- correction is also now controlled by HARDME for consistency. * Soft matrix element corrections have been introduced in DIS and e+e- processes. These correct the distribution of emissions within the parton shower phase-space. It is similar to the method used in JETSET, except that the HARDEST emission is matched to the leading order matrix element, not the first as in JETSET. This ensures that the correction enters into the form factor, and not just the real emission probability. * In the backward evolution of initial-state radiation for photons the anomalous branching q-qbar <-- gamma has been introduced. * The treatment of forced branching of gluons and sea (anti-)quarks in backward evolution has been improved, by allowing it to occur at a random scale between the space-like cutoff QSPAC and the infrared cutoff, instead of exactly at QSPAC as before. A new option ISPAC=2 allows the freezing of structure functions at the scale QSPAC, while evolution continues to the infrared cutoff. The default, ISPAC=0 is equivalent to previous versions, in which perturbative evolution stops at QSPAC. * It is now possible to completely switch off initial-state radiation, by setting NOSPAC =.TRUE. Only the forced splitting of non-valence partons is generated. The default is (of course) NOSPAC =.FALSE. * An option to damp the parton distributions of off mass-shell photons relative on-shell photons, according to the scheme defined in Drees and Godbole MAD/PH/819 has been introduced. The adjustable parameter PHOMAS defines the crossover from the non-suppressed to suppressed regimes. Recommended values lie in the range QCDLAM to 1 GeV. The default value PHOMAS=0. corresponds to no suppression as in previous versions. * The interface to PDFLIB version 4 has been slightly changed. Instead of indicating a PDF set by a unique number, an `author group' string and set number are required. PDFLIB version 3 can still be used from HERWIG, simply by setting the author group to 'MODE'. It is also now possible to independently set the PDF set for each of the two beams. For example, if you previously used MRS D- for the proton and Gordon -Storrow set 1 for the photon, by setting MODPDF=47 MODPHO=231 You should now set AUTPDF(2)='MRS' MODPDF(2)=28 AUTPDF(1)='GS' MODPDF(1)=2 Alternatively, if you are still using PDFLIB version 3, you can set AUTPDF(2)='MODE' MODPDF(2)=47 AUTPDF(1)='MODE' MODPDF(1)=231 * In the CLDIR=1 option for cluster decays a new parameter CLSMR (default = 0.) allows a Gaussian smearing of the direction of the perturbative quark's momentum. The smearing is actually exponential in 1-cos(theta) with mean CLSMR. Thus increasing CLSMR decorrelates the cluster decay from the initial quark direction. * New subprocess have been added: - The direct, higher twist, production of light (u,d,s) L=0 mesons by point-like photons is now available: IPROC = 5500 all Spin =0,1 mesons, = 5510 only S=0 mesons; = 5520 only S=1 mesons. The vector mesons are produced with transverse or longitudinal polarisation and decayed accordingly. - High transverse momentum, scalar Higgs production, in association with a jet, is now available as IPROC =2300. Only the top quark is included in the loops with IAPHIG controlling the approx. used: =0 zero top mass limit; = 1 exact result; = 2 infinite top mass limit (default 1). Note the routines: HWHGJ1, HWHGJA, HWHGJB/C/D, HWUCI2 and HWULI2 use (non-standard FORTRAN-77) DOUBLE COMPLEX variables which may not be accepted by some compilers. Users can change to COMPLEX variables, however this involves a risk of rounding errors spoiling numerical cancellations. - DIS with neutrino beams is now available in processes IPROC= 90**. * The DIS O(alpha_s) jet production processes, IPROC = 92**, have been withdrawn and are no longer supported. * A running electromagnetic coupling has been introduced, HWUAEM(Q2). ALPHEM (now a single variable) sets the Thomson limit (Q2=0) value, default = 0.0072993 (1/137.0). * Two new particles have been created: 'REMG', IDHW=71, IDHEP=9998 and 'REMN', IDHW=72, IDHEP=9999 are remnant photons and nucleons respectively. They are identical to photons & nucleons, except that gluons are labelled as valence partons and, for the nucleon, valence quark distributions are set to zero. They are used internally by the JIMMY generator for multiple interactions, and are not intended for general use. * An error in setting the scale EMCMF (now called EMSCA) for QCD decays of colour neutral particles, preventing parton showers, has been corrected. * Minor bugs have been corrected in: phi decays to neutral kaons; the weights for photo-production processes; the value of EVWGT in di-jet production by point-like photons. * The transverse momentum cutoff for final-state photon emission from quarks, VPCUT, now defaults to 0.4 GeV. Previous versions defaulted to SQRT(S), switching off such emission. * The default top quark mass has been increased to 170 GeV/c^2 ------------------------------------------------------------------------ ****** 3. FEATURES NOT YET INCLUDED ****** Note that the following features are NOT yet included in the program: polarization of produced heavy quarks and leptons; treatment of coherence in the small-x region of incoming jets (see S. Catani, F. Fiorani and G. Marchesini, Nucl.Phys. B336(1990)18); multiple parton interactions and parton shadowing; diffractive processes; W/Z bosons within parton showers. ------------------------------------------------------------------------ ****** 4. PROGRAM STRUCTURE ****** The main program HWIGPR has the following form: PROGRAM HWIGPR C---COMMON BLOCKS ARE INCLUDED AS FILE HERWIG59.INC INCLUDE 'HERWIG59.INC' INTEGER N C---MAX NUMBER OF EVENTS THIS RUN MAXEV=100 C---BEAM PARTICLES PART1='PBAR' PART2='P' C---BEAM MOMENTA PBEAM1=900. PBEAM2=900. C---PROCESS IPROC=1500 C---INITIALISE OTHER COMMON BLOCKS CALL HWIGIN C---USER CAN RESET PARAMETERS AT C THIS POINT, OTHERWISE DEFAULT C VALUES IN HWIGIN WILL BE USED. PTMIN=100. C---COMPUTE PARAMETER-DEPENDENT CONSTANTS CALL HWUINC C---CALL HWUSTA TO MAKE ANY PARTICLE STABLE CALL HWUSTA('PI0 ') C---USER'S INITIAL CALCULATIONS CALL HWABEG C---INITIALISE ELEMENTARY PROCESS CALL HWEINI C---LOOP OVER EVENTS DO 100 N=1,MAXEV C---INITIALISE EVENT CALL HWUINE C---GENERATE HARD SUBPROCESS CALL HWEPRO C---GENERATE PARTON CASCADES CALL HWBGEN C---DO HEAVY QUARK DECAYS CALL HWDHQK C---DO CLUSTER FORMATION CALL HWCFOR C---DO CLUSTER DECAYS CALL HWCDEC C---DO UNSTABLE PARTICLE DECAYS CALL HWDHAD C---DO HEAVY FLAVOUR HADRON DECAYS CALL HWDHVY C---ADD SOFT UNDERLYING EVENT IF NEEDED CALL HWMEVT C---FINISH EVENT CALL HWUFNE C---USER'S EVENT ANALYSIS CALL HWANAL 100 CONTINUE C---TERMINATE ELEMENTARY PROCESS CALL HWEFIN C---USER'S TERMINAL CALCULATIONS CALL HWAEND STOP END Various phases of the simulation can be suppressed by deleting the corresponding subroutine calls, or different subroutines may be substituted. For example, in studies at the parton level everything from CALL HWDHQK to CALL HWMEVT can be omitted. The following is a full list of subroutines and functions, which are classified according to their initial letters, except when standard- ization agreements take precedence. +--------+---------------------------------------------+ | Name | Description | +--------+---------------------------------------------+ | Main program and initialization | +--------+---------------------------------------------+ | HWIGPR | Main program | | HWIGIN | Default initializations | +--------+---------------------------------------------+ | Reading/writing/altering decay modes | +--------+---------------------------------------------+ | HWIODK | Inputs/outputs formatted decay tables | | HWMODK | Modifies or adds an individual decay mode | +--------+---------------------------------------------+ | User-provided analysis routines | +--------+---------------------------------------------+ | HWABEG | Initializes user's analysis | | HWAEND | Terminates user's analysis | | HWANAL | Performs user's analysis on event | +--------+---------------------------------------------+ | Parton branching with interfering gluons | +--------+---------------------------------------------+ | HWBAZF | Computes azimuthal correlation functions | | HWBCON | Makes colour connections between jets | | HWBDED | Correction to the `dead zone' in e+e- | | HWBDIS | Correction to the `dead zone' in DIS | | HWBFIN | Transfers external lines of jet to /HEPEVT/ | | HWBGEN | Finds unevolved partons and generates jets | | HWBJCO | Combines jets with correct kinematics | | HWBMAS | Computes masses and trans. momenta in jet | | HWBRAN | Generates a timelike parton branching | | HWBSPA | Computes momenta in spacelike jet | | HWBSPN | Computes spin density/decay matrices | | HWBSU1 | First term in quark Sudakov form factor | | HWBSU2 | Second term in quark Sudakov form factor | | HWBSUD | Computes (or reads) Sudakov form factors | | HWBSUG | Integrand in gluon Sudakov form factor | | HWBSUL | Logarithmic part of Sudakov form factor | | HWBTIM | Computes momenta in timelike jet | | HWBVMC | Virtual mass cutoff for parton type ID | +--------+---------------------------------------------+ | Cluster hadronization model | +--------+---------------------------------------------+ | HWCCUT | Cuts a massive cluster in two | | HWCDEC | Decays clusters into primary hadrons | | HWCFLA | Sets up flavours for HWCHAD | | HWCFOR | Forms clusters | | HWCGSP | Splits gluons | | HWCHAD | Decays a cluster into one or two hadrons | +--------+---------------------------------------------+ | Particle and heavy quark decays | +--------+---------------------------------------------+ | HWDBOS | Finds and decays W and Z bosons | | HWDBOZ | Chooses decay mode of W and Z bosons | | HWDCLE | Interface to CLEO package for B decays | | HWDCHK | Checks given decay mode is self-consistent | | HWDFOR | Generates a four-body decay | | HWDFIV | Generates a five-body decay | | HWDEUR | Interface to EURODEC package for B decays | | HWDHAD | Generates decays of unstable hadrons | | HWDHGC | Higgs -> gamma gamma decay | | HWDHGF | Higgs -> W+ W- decay | | HWDHIG | Finds and decays Higgs bosons | | HWDHQK | Finds and decays heavy quarks | | HWDHVY | Finds and decays heavy flavour hadrons | | HWDIDP | Chooses a parton for HWDHVY | | HWDPWT | Phase space decay weight | | HWDTHR | Generates a three-body decay | | HWDTOP | Decides whether to decay top quark | | HWDTWO | Generates a two-body decay | | HWDWWT | Weak (V-A) decay weight | | HWDXLM | Tests if decay vertex lies in given volume | +--------+---------------------------------------------+ | Elementary subprocess generation | +--------+---------------------------------------------+ | HWEFIN | Final calculations on elementary subprocess | | HWEGAM | Generates Weizsacker-Williams photon | | HWEINI | Initializes elementary subprocess | | HWEISR | Generates a photon fron initial e or mu | | HWEONE | Sets up a 2->1 hard subprocess | | HWEPRO | Generates elementary subprocess | | HWETWO | Sets up a 2->2 hard subprocess | +--------+---------------------------------------------+ | Individual hard subprocesses | +--------+---------------------------------------------+ | HWHBGF | Hard subprocess: boson-gluon fusion (BGF) | | HWHBKI | Computes kinematics for BGF | | HWHBRN | Returns a phase-space point for BGF | | HWHBSG | Computes cross section for BGF | | HWHDIS | Hard subprocess: deep inelastic lepton quark| | HWHDYP | Hard subprocess: Drell-Yan Z0/photon prodn | | HWHEGG | Hard subprocess: two-photon processes in ee | | HWHEGW | Hard subprocess: photon-W processes in e+e- | | HWHEGX | Calculates cross section for HWHEGW | | HWHEPA | Hard subprocess: e+e- -> f fbar | | HWHEPG | Hard subprocess: e+e- -> q qbar gluon | | HWHEW0 | e+e- -> W W / Z Z subroutine | | HWHEW1 | e+e- -> W W / Z Z subroutine | | HWHEW2 | e+e- -> W W / Z Z subroutine | | HWHEW3 | e+e- -> W W subroutine | | HWHEW4 | e+e- -> W W / Z Z subroutine | | HWHEW5 | e+e- -> Z Z subroutine | | HWHEWW | Hard subprocess: e+e- -> W W / Z Z | | HWHHVY | Hard subprocess: heavy quark production | | HWHIG1 | Matrix elements for Higgs + jet production | | HWHIGA | Amplitudes squared for Higgs + jet | | HWHIGB | Loop integrals for Higgs + jet | | HWHIGJ | QCD Higgs + jet production | | HWHIGM | Choose Higgs mass for production routines | | HWHIGS | Hard subprocess: gg/qqbar -> Higgs | | HWHIGT | Computes gg -> Higgs cross section | | HWHIGW | Hard subprocess: WW / ZZ -> Higgs | | HWHIGY | Computes ee -> Z -> ZH cross section | | HWHIGZ | Hard subprocess: ee -> Z -> ZH | | HWHPH2 | Hard subprocess: direct photon pairs | | HWHPHO | Hard subprocess: direct photon production | | HWHPPB | Box contribution to gg->photon photon | | HWHPPE | Pointlike photon-parton (fixed flavour) | | HWHPPH | Pointlike photon-parton (fixed pair flavour)| | HWHPPM | Pointlike photon-parton direct light meson | | HWHPPT | Pointlike photon-parton (all flavours) | | HWHQPS | Pointlike photon-quark (Compton) scattering | | HWHQCD | Hard subprocess: QCD 2->2 | | HWHQCP | Identifies QCD 2->2 hard subprocess | | HWHREM | Treats hard scattering remnants | | HWHSCT | Process extra hard scatterings | | HWHSNG | Colour singlet parton scattering | | HWHSNM | Colour singlet parton scattering ME | | HWHV1J | Hard subprocess W/Z + jet production | | HWHWEX | Top production by W exchange | | HWHWPR | Hard subprocess: W production | +--------+---------------------------------------------+ | Soft minimum-bias or underlying event | +--------+---------------------------------------------+ | HWMEVT | Generates min bias or soft underlying event | | HWMLPS | Generates longitudinal phase space | | HWMNBI | Computes negative binomial probability | | HWMULT | Chooses min bias charged multiplicity | | HWMWGT | Calculates weight for minimum bias events | +--------+---------------------------------------------+ | Random number generators | +--------+---------------------------------------------+ | HWRAZM | Randomly rotated azimuth | | HWREXP | Random number: exponential distribution | | HWREXQ | Random number: exp. dist. with cutoff | | HWREXT | Random number: exponential transverse mass | | HWRGAU | Random number: Gaussian | | HWRGEN | Random number generator (l'Ecuyer method) | | HWRINT | Random integer | | HWRLOG | Random logical | | HWRPIP | Random primary interaction point | | HWRPOW | Random number: power distribution | | HWRUNG | Random number: uniform + Gaussian tails | | HWRUNI | Random number: uniform | +--------+---------------------------------------------+ | Spacelike branching of incoming partons | +--------+---------------------------------------------+ | HWSBRN | Generates spacelike parton branching | | HWSDGG | Drees-Grassie photon str. function (gluon) | | HWSDGQ | Drees-Grassie photon str. function (quarks) | | HWSFBR | Chooses a spacelike branching | | HWSFUN | Hadron structure functions | | HWSGAM | Gamma function (for structure functions) | | HWSGEN | Generates x values for spacelike partons | | HWSGQQ | Inserts g->q qbar part of gluon form factor | | HWSSPC | Replaces spacelike partons by spectators | | HWSSUD | Sudakov form factor/structure function | | HWSTAB | Interpolates in function table (for HWSSUD) | | HWSVAL | Checks for valence parton | +--------+---------------------------------------------+ | Miscellaneous utilities | +--------+---------------------------------------------+ | HWUAEM | Running electromagnetic coupling constant | | HWUAER | Real part of photon self-energy | | HWUALF | Two-loop QCD running coupling constant | | HWUANT | Finds a particle's antiparticle | | HWUBPR | Prints branching data for last parton shower| | HWUBST | Boost event record to/from hadron-hadron cmf| | HWUCFF | Coefficients for e+e- and DIS cross sections| | HWUCI2 | Logarithmic integral Ci_2 | | HWUDAT | Block data: particle properties | | HWUDKL | Generates decay vertex of unstable particle | | HWUDKS | Converts decay modes into internal format | | HWUDPR | Prints particle properties and decay modes | | HWUECM | Centre-of-mass energy | | HWUEDT | Insert or delete entries in the event record| | HWUEEC | Computes coefficients for e+e- cross section| | HWUEPR | Prints event data | | HWUEMV | Moves entries within the event record | | HWUFNE | Finishes an event | | HWUGAU | Adaptive Gaussian integration | | HWUIDT | Translates particle identity codes | | HWUINC | Initial parameter-dependent calculations | | HWUINE | Initializes an event | | HWULB4 | Boost: rest frame -> lab, no masses assumed | | HWULDO | Lorentz 4-vector dot product | | HWULF4 | Boost: lab frame -> rest, no masses assumed | | HWULI2 | Logarithmic integral Li_2 (Spence function) | | HWULOB | Lorentz transformation: rest frame -> lab | | HWULOF | Lorentz transformation: lab -> rest frame | | HWULOR | Multiplies by Lorentz matrix | | HWUMAS | Puts mass in 5th component of vector | | HWUPCM | Centre-of-mass momentum | | HWURAP | Rapidity | | HWURES | Computes/prints resonance data | | HWUROB | Rotation by inverse of matrix R | | HWUROF | Rotation by matrix R | | HWUROT | Computes rotation R from vector to z-axis | | HWUSOR | Sorts an array in ascending order | | HWUSQR | Square root with sign retention | | HWUSTA | Makes a particle type stable | | HWUTAB | Interpolates in a table | | HWUTIM | Checks time remaining (N.B. VAX Fortran) | +--------+---------------------------------------------+ | Vector manipulation | +--------+---------------------------------------------+ | HWVDIF | Vector difference | | HWVDOT | Vector dot product | | HWVEQU | Vector equality | | HWVSCA | Vector times scalar | | HWVSUM | Vector sum | | HWVZRO | Vector zero | +--------+---------------------------------------------+ | Warning messages and error handling | +--------+---------------------------------------------+ | HWWARN | Issues warnings and deals with errors | +--------+---------------------------------------------+ N.B. Dummy versions of the external routines PDFSET STRUCTM EUDINI FRAGMT IEUPDG IPDGEU DECADD QQINIT QQLMAT HVCBVI HVHBVI should be deleted if the structure function library, EURODEC B decay package, CLEO B decay package, or HERBVI (respectively) is linked. ------------------------------------------------------------------------ ****** 5. BEAMS AND PROCESSES ****** As indicated above, a number of variables must be set in the main program to specify what is to be simulated: +----------+----------------------------------+-----------+ | Name | Description | Default | +----------+----------------------------------+-----------+ | PART1 | Type of particle in beam 1 | 'PBAR '| | PART2 | Type of particle in beam 2 | 'P '| | PBEAM1 | Momentum of beam 1 | 900. | | PBEAM2 | Momentum of beam 2 | 900. | | IPROC | Type of process to generate | 1500 | | MAXEV | Number of events to generate | 100 | +----------+----------------------------------+-----------+ The beam particle types PART1,PART2 supported at present are: +---------------------------------------------+ | 'E+ ','E- ','MU+ ','MU- ' | | 'NUE ','NUEB ','NUMU ','NMUB ' | | 'NTAU ','NTAB ','GAMA ' | | 'P ','PBAR ','N ','NBAR ' | | 'PI+ ','PI- ' | +---------------------------------------------+ In addition, beams 'K+ ' and 'K- ' are supported for minimum bias non-diffractive soft hadronic events (IPROC=8000) only. The currently available processes IPROC are tabulated below. +---------+--------------------------------------------------------+ | IPROC | Process | +---------+--------------------------------------------------------+ | 100 | e+ e- -> q qbar (gluon) (all flavours) | | 100+IQ | e+ e- -> q qbar (gluon) (IQ=1--6 for q=d,u,s,c,b,t) | | 107 | e+ e- -> gluon gluon (gluon) fictitious process | | 110 | e+ e- -> q qbar gluon (all flavours) | | 110+IQ | e+ e- -> q qbar gluon (IQ as above) | | 120 | e+ e- -> q qbar (all flavours)| without correction to | | 120+IQ | e+ e- -> q qbar (IQ as above) | hard gluon branching | | 127 | e+ e- -> gluon gluon | | | 150+IL | e+ e- -> l lbar (IL=2,3 for l=mu,tau) | +---------+--------------------------------------------------------+ | 200 | e+ e- -> W+ W- (see sect. 18 on control of W/Z decays)| | 250 | e+ e- -> Z0 Z0 (see sect. 18 on control of W/Z decays)| +---------+--------------------------------------------------------+ | 300 | e+ e- -> Z H -> Z q qbar (all flavours) | | 300+IQ | e+ e- -> Z H -> Z q qbar (IQ as above) | | 306+IL | e+ e- -> Z H -> Z l lbar (IL=1,2,3 for l=e,mu,tau) | | 310,11 | e+ e- -> Z H -> Z W W, Z Z Z | | 312 | e+ e- -> Z H -> Z gamma gamma | | 399 | e+ e- -> Z H -> Z anything | +---------+--------------------------------------------------------+ | 400+ID | e+ e- -> nu nu H + e e H (ID as in IPROC=300+ID) | +---------+--------------------------------------------------------+ | 500+ID | e+ e- -> gamma gamma -> qqbar/llbar/WW (ID=0-10 as in | | | IPROC=300+ID) | | 550+ID | e+ e- -> gamma W -> qq'bar/ll'bar (ID=0-9) | +---------+--------------------------------------------------------+ | 1300 | q qbar -> Z0/gamma -> q qbar (all flavours) | | 1300+IQ | q qbar -> Z0/gamma -> q qbar (IQ as above) | | 1350 | q qbar -> Z0/gamma -> l lbar (all lepton species) | | 1350+IL | q qbar -> Z0/gamma -> l lbar (IL=1-6 for e,enu,mu,etc) | | 1399 | q qbar -> Z0/gamma -> anything | +---------+--------------------------------------------------------+ | 1400 | q qbar -> W+/- -> q' qbar'' (all flavours) | | 1400+IQ | q qbar -> W+/- -> q' qbar'' (q' or q'' as above) | | 1450 | q qbar -> W+/- -> l nul (all lepton species) | | 1450+IL | q qbar -> W+/- -> l nul (IL=1-3 as above) | | 1499 | q qbar -> W+/- -> anything | +---------+--------------------------------------------------------+ | 1500 | QCD 2 -> 2 hard parton scattering | | | After generation, IHPRO is subprocess (see list) | +---------+--------------------------------------------------------+ | 1600+ID | q qbar/g g -> Higgs (ID as in IPROC=300+ID) | +---------+--------------------------------------------------------+ | 1700+IQ | QCD heavy quark production (IQ as above) | | | After generation, IHPRO is subprocess (see list) | +---------+--------------------------------------------------------+ | 1800 | QCD direct photon + jet production | | | After generation, IHPRO is subprocess (see list) | +---------+--------------------------------------------------------+ | 1900+ID | q qbar -> q' qbar' H (ID as in IPROC=300+ID) | +---------+--------------------------------------------------------+ | 2000 | t production via W exchange (sum of 2001-2008) | | 2001,2 | ubar bbar -> dbar tbar, d bbar -> u tbar | | 2003,4 | dbar bbar -> ubar tbar, u b -> d t | | 2005,6 | cbar bbar -> sbar tbar, s bbar -> c tbar | | 2007,8 | sbar b -> cbar t , c b -> s t | +---------+--------------------------------------------------------+ | 2100 | Vector boson + jet production. | | 2110,20 | Compton only (g q -> V q), annih. only (q qbar -> V g) | +---------+--------------------------------------------------------+ | 2200 | QCD direct photon pair production (see list for IHPRO) | +---------+--------------------------------------------------------+ | 2300 | QCD Higgs plus jet production (see list for IHPRO) | +---------+--------------------------------------------------------+ | 2400 | Mueller-Tang colour singlet exchange | | 2450 | Quark scattering via photon exchange | +---------+--------------------------------------------------------+ | 5000 | Pointlike photon-hadron jet production (all flavours) | | 5100+IQ | Pointlike photon heavy flavour IQ pair production | | 5200+IQ | Pointlike photon heavy flavour IQ single excitation | | | After generation, IHPRO is subprocess (see list) | | 5300 | Quark photon Compton scattering | | 5500 | Pointlike photon production of light (u,d,s) L=0 mesons| | 5510,20 | S=0 mesons only, S=1 mesons only (see list for IHPRO) | +---------+--------------------------------------------------------+ | 7000 - | Baryon-number violating and other multi-W processes | | 7999 | generated by HERBVI package | +---------+--------------------------------------------------------+ | 8000 | Minimum bias non-diffractive soft hadron-hadron event | +---------+--------------------------------------------------------+ | 9000 | Deep inelastic lepton scattering (all neutral current) | | 9000+IQ | Deep inelastic lepton scattering (NC on flavour IQ) | | 9010 | Deep inelastic lepton scattering (all charged current) | | 9010+IQ | Deep inelastic lepton scattering (CC on flavour IQ) | +---------+--------------------------------------------------------+ | 9100 | Boson-gluon fusion in NC DIS, all flavours | | 9100+IQ | Boson-gluon fusion in NC DIS, IQ=1-6 as above | | 9107 | J/Psi + gluon production by boson-gluon fusion | | 9110 | QCD Compton process in NC DIS, all flavours | | 9110+IP | QCD Compton process in NC DIS, IP=1-12, d-t, dbar-tbar | | 9130 | All O(alpha-s) NC processes: 9100+9110 | | 9140+IP | CC proc, IP:1 = s cbar,2 = b cbar,3 = s tbar,4 = b tbar| +---------+--------------------------------------------------------+ | 92** | Withdrawn: use 91** instead | +---------+--------------------------------------------------------+ | 9500+ID | W W fusion -> Higgs in e p (ID as in IPROC=300+ID) | +---------+--------------------------------------------------------+ |10000+IP | as IPROC=IP but with soft underlying event (hadron | | | remnant fragmentation in lepton-hadron) suppressed | +---------+--------------------------------------------------------+ The extent to which quark mass effects are included in the hard process cross section is different in different processes. In many processes, they are always treated as massless: IPROC=1300, 1800, 1900, 2100, 2300, 2400, 5300, 9000. In two processes they are all treated as massless except the top quark, for which the mass is correctly incorporated: 1400, 2000. In the case of massless pair production, only quark flavours that are kinematically allowed are produced. In all cases the event kinematics incorporate the quark mass, even when it is not used to calculate the cross section. In two processes, quarks are always treated as massive: 500, 9100. Finally, in several processes, the behaviour is different depending on whether a specific quark flavour is requested, in which case its mass is included, or not, in which case all quarks are treated as massless. These are: IPROC=100, 110, 120, QCD 2->2 scattering (1500 vs 1700+IQ), jets in direct photoproduction (5000 vs 5100+IQ and 5200+IQ). These differences can cause inconsistencies between different ways of generating the same process. The most noticeable example is in direct photoproduction, where one can use process 9130, which uses the exact 2->3 matrix element e+g --> e+q+qbar, or process 5000, which uses the Weizsacker-Williams spectrum for e --> e+gamma and the 2->2 matrix element for gamma+g --> q+qbar. For typical HERA kinematics, the W-W approximation is valid to a few per cent, but the difference between the two processes is much larger, about 20% for PTMIN=2 GeV. This is entirely due to the difference in quark mass treatments, as can be checked by comparing process 9130 with processes 5100+IQ and 5200+IQ summed over IQ ------------------------------------------------------------------------ ****** 6. INPUT PARAMETERS ****** The quantities that may be regarded as adjustable parameters are +----------+----------------------------------+-------+ | Name | Description |Default| +----------+----------------------------------+-------+ | QCDLAM | QCD Lambda (see below) | 0.18 | +----------+----------------------------------+-------+ | RMASS(1) | Down quark mass | 0.32 | | RMASS(2) | Up quark mass | 0.32 | | RMASS(3) | Strange quark mass | 0.50 | | RMASS(4) | Charmed quark mass | 1.55 | | RMASS(5) | Bottom quark mass | 4.95 | | RMASS(6) | Top quark mass | 170. | +----------+----------------------------------+-------+ | RMASS(13)| Gluon effective mass | 0.75 | +----------+----------------------------------+-------+ | VQCUT | Quark virtuality cutoff (added to| 0.48 | | | quark masses in parton showers) | | | VGCUT | Gluon virtuality cutoff (added to| 0.10 | | | effective mass in parton showers)| | | VPCUT | Photon virtuality cutoff | 0.40 | +----------+----------------------------------+-------+ | CLMAX | Maximum cluster mass parameter | 3.35 | | CLPOW | Power in maximum cluster mass | 2.00 | | PSPLT | Split cluster spectrum parameter | 1.00 | +----------+----------------------------------+-------+ | QDIQK | Maximum scale for gluon->diquarks| 0.00 | | PDIQK | Gluon->diquarks rate parameter | 5.00 | +----------+----------------------------------+-------+ | QSPAC | Cutoff for spacelike evolution | 2.50 | | PTRMS | Intrinsic pt in incoming hadrons | 0.00 | +----------+----------------------------------+-------+ Notes on parameters: * QCDLAM can be identified at high momentum fractions (x or z) with the fundamental QCD scale Lambda-MSbar (5 flavours). However, this relation does not necessarily hold in other regions of phase space, since higher order corrections are not treated precisely enough to remove renormalization scheme ambiguities. See S. Catani, G. March- esini and B.R.Webber, Nucl. Phys. B349 (1991) 635. * RMASS(1,2,3,13) are effective light quark and gluon masses used in the hadronization phase of the program. They can be set to zero provided the parton shower cutoffs VQCUT and VGCUT are large enough to prevent divergences (see below). * For cluster hadronization, it must be possible to split gluons into q-qbar, i.e. RMASS(13) must be at least twice the lightest quark mass. Similarly it may be impossible for heavy flavoured clusters to decay if RMASS(4,5) are too low. * VQCUT and VGCUT are needed if the quark and gluon effective masses become small. The condition to avoid divergences in parton showers is 1/Q(i) + 1/Q(j) < 1/QCDL3 for either i or j or both gluons, where Q(i)=RMASS(i)+VQCUT for quarks, RMASS(13)+VGCUT for gluons, and QCDL3 is the equivalent 3-flavour Lambda computed from QCDLAM. In the notation of the above reference by S. Catani et al., QCDL3 is the 3-flavour equivalent of QCDL5 where QCDL5 = QCDLAM*exp(K/(4*pi*beta))/sqrt(2)=1.109*QCDLAM * VPCUT is the analogous quantity for photon emission. It defaults to SQRT(S) corresponding to no emission. Results after experimental cuts are insensitive to its exact value in the range 0.1 to 1.0 GeV * CLMAX and CLPOW determine the maximum allowed mass of a cluster made from quarks i and j as follows Mass**CLPOW < CLMAX**CLPOW + (RMASS(i)+RMASS(j))**CLPOW Since the cluster mass spectrum falls rapidly at high mass, results become insensitive to CLMAX and CLPOW at large values of CLMAX. Smaller values OF CLPOW will increase the yield of heavier clusters (and hence of baryons) for heavy quarks, without affecting light quarks much. For example, the default value gives no b-baryons whereas CLPOW=1.0 makes b-baryons/b-hadrons about 1/4. * PSPLT determines the mass distribution in the cluster splitting CL1 -> CL2 + CL3 when CL1 is above the maximum allowed mass. The masses of CL2 and CL3 are generated uniformly in Mass**PSPLT. Since the number of split clusters is small, dependence on PSPLT is weak. * QDIQK greater than twice the lightest diquark mass enables gluons to split non-perturbatively into diquarks as well as quarks. The probability of this is PDIQK*dQ/Q for scales Q below QDIQK. The diquark masses are taken to be the sum of constituent quark masses. Thus the default value QDIQK=0 suppresses gluon->diquark splitting. * QSPAC is the scale below which the structure functions of incoming hadrons are frozen and non-valence constituent partons are forced to evolve to valence partons, if ISPAC=0. For ISPAC=2, structure functions are frozen at scale QSPAC, but evolution continues down to the infrared cutoff. * PTRMS is the width of the (Gaussian) intrinsic transverse momentum distribution of valence partons in incoming hadrons at scale QSPAC. (N.B. Neither QSPAC nor PTRMS affect lepton-lepton collisions.) In practice, the parameters that have been found most effective in fitting data are QCDLAM, the gluon effective mass RMASS(13), and the cluster mass parameter CLMAX. The default parameter values have been found to give good agreement with event shape distributions at LEP (OPAL preprint CERN-EP/90-48). A number of further parameters are needed to control the program and to turn various options on or off: +----------+----------------------------------+-------+ | Name | Description |Default| +----------+----------------------------------+-------+ | IPRINT | Printout option | 1 | | MAXPR | Number of events to print out | 1 | | PRVTX | Include vertex info in print out | .TRUE.| | MAXER | Max number of errors | 10 | | LWEVT | Unit for writing output events | 0 | | LRSUD | Unit for reading Sudakov table | 0 | | LWSUD | Unit for writing Sudakov table | 77 | | SUDORD | Alpha_s order in Sudakov table | 1 | +----------+----------------------------------+-------+ | NRN(1) | Random number seed 1 | 17673 | | NRN(2) | Random number seed 2 | 63565 | | WGTMAX | Max weight (0 to search for it) | 0. | | NOWGT | Generate unweighted events | .TRUE.| +----------+----------------------------------+-------+ | AZSOFT | Soft gluon azimuthal correlations| .TRUE.| | AZSPIN | Gluon spin azimuthal correlations| .TRUE.| +----------+----------------------------------+-------+ | NCOLO | Number of colours | 3 | | NFLAV | Number of (producible) flavours | 6 | +----------+----------------------------------+-------+ | MODPDF(I)| PDFLIB structure function set and| -1 | | AUTPDF(I)| author group for beam I(=1,2) | 'MRS' | | | (if MODPDF()<0 do not use PDFLIB)| | | NSTRU | Input structure function set | 5 | | | (1,2=Duke-Owens1,2 3,4=EHLQ1,2 | | | | 5=Owens1.1) | | +----------+----------------------------------+-------+ | ETAMIX | eta/eta' mixing angle in degrees | -20 | | | F0Mix.. +----------+----------------------------------+-------+ | B1LIM | B cluster -> 1 hadron parameter | 0.0 | +----------+----------------------------------+-------+ | CLDIR | Decay of perturbative clusters, | 1 | | | 0=>isotropic, 1=>along quark dirn| | | CLSMR | Width of Gaussian angle smearing | 0.0 | +----------+----------------------------------+-------+ | CLRECO | Include colour rearrangement |.FALSE | | PRECO | Probability for rearrangement | 1./9. | | EXAG | Lifetime scaling for weak bosons | 1. | +----------+----------------------------------+-------+ | PIPSMR | Smear the primary vertex | .TRUE.| | MAXDKL | Veto decays outside given volume |.FALSE.| +----------+----------------------------------+-------+ | HARDME | Use hard and soft matrix-element | .TRUE.| | SOFTME | corrections to e+e- and DIS | .TRUE.| +----------+----------------------------------+-------+ | BDECAY | Controls which B Decay package is| 'HERW'| | | used. The allowed values are: | | | | 'HERW'; 'EURO'; or 'CLEO'. | | | MIXING | Include neutral B meson mixing | .TRUE.| | XMIX(2) | Mass difference I=1 B^0_s | 10.0 | | | average width 2 B^0_d | 0.70 | | YMIX(2) | Width difference I=1 B^0_s | 0.20 | | | average width 2 B^0_d | 0.00 | +----------+----------------------------------+-------+ | EPOLN(3) | Electron and positron beam | 0.0 | | | polarizations in DIS and e+e- | 0.0 | | | annihilation. First two cmpts are| 0.0 | | PPOLN(3) | transverse and only used in e+e-,| 0.0 | | | 3rd cmpt is longitudinal, and is | 0.0 | | | +/-1 for fully rh/lh polarized | 0.0 | +----------+----------------------------------+-------+ | BGSHAT | Scale=shat for boson-gluon fusion|.FALSE.| +----------+----------------------------------+-------+ | BREIT | Use Breit frame for DIS kinematix| .TRUE.| +----------+----------------------------------+-------+ | USECMF | Use hadron-hadron cmf | .TRUE.| +----------+----------------------------------+-------+ | NOSPAC | Switch off space-like showers |.FALSE.| +----------+----------------------------------+-------+ | ISPAC | Changes meaning of QSPAC, | 0 | | | see the earlier notes on QSPAC | | +----------+----------------------------------+-------+ | TMNISR | Min vaule shat/S for photon ISR | 1D-4 | | ZMXISR | Max mom fraction for photon ISR | 1-1D-6| +----------+----------------------------------+-------+ | PTMIN | Min pt in hadronic jet production| 10. | | PTMAX | Max pt in hadronic jet production| 1.E8 | | PTPOW | 1/pt**PTPOW for jet sampling | 4. | | YJMIN | Min jet rapidity |-8. | | YJMAX | Max jet rapidity | 8. | +----------+----------------------------------+-------+ | EMMIN | Min dilepton mass in Drell-Yan | 10. | | EMMAX | Max dilepton mass in Drell-Yan | 1.E8 | | EMPOW | 1/m**EMPOW for Drell-Yan sampling| 4. | +----------+----------------------------------+-------+ | Q2MIN | Min Q**2 in deep inelastic | 0.0 | | Q2MAX | Max Q**2 in deep inelastic | 1.E10 | | Q2POW | (1/Q**2)**Q2POW for sampling | 2.5 | +----------+----------------------------------+-------+ | Q2WWMN | Min Q**2 in Equiv Photon Approx | 0.0 | | Q2WWMX | Max Q**2 in Equiv Photon Approx | 4.0 | +----------+----------------------------------+-------+ | YWWMIN | Min energy of gamma in WW approx | 1.0 | | YWWMAX | Max energy of gamma in WW approx | 0.0 | +----------+----------------------------------+-------+ | PHOMAS | Damp structure functions for off-| 0.0 | | | shell photons (0 for no damping) | | +----------+----------------------------------+-------+ | YBMIN | Min and Max Bjorken-y in DIS and | 0.0 | | YBMAX | Equivalent Photon Approx | 1.0 | +----------+----------------------------------+-------+ | ZJMAX | Max Z in J/psi production | 0.9 | +----------+----------------------------------+-------+ | THMAX | Max thrust in 3 parton production| 0.9 | | | (equal to 1-Y_cut in JADE scheme)| | +----------+----------------------------------+-------+ Printout options are: IPRINT = 0 Print program title only 1 Print selected input parameters 2 1 + table of particle codes and properties 3 2 + tables of Sudakov form factors PRVTX = .T. To include the production vertex information in the event print out, requires wide screen format. See sect. 8 on form factors for details of LRSUD, LWSUD and SUDORD. If BGSHAT is false, the scale used for heavy quark production via boson-gluon fusion in lepton-hadron collisions will be 2*shat*that*uhat/(shat**2+that**2+uhat**2) If BREIT is true, the kinematic reconstruction of deep inelastic events takes place in the Breit frame (ie. the frame where the exchanged boson is purely space-like, and collinear with the incoming hadron). In fact the reconstruction procedure is invariant under longitudinal boosts, so any frame in which the boson and hadron are collinear would be equivalent, and it is only the transverse part of the boost that has an effect. The BREIT frame option becomes very inaccurate for very small Q^2. It is therefore only used if Q**2 > 1E-4 (the lab and Breit frames are anyway equivalent for such small Q**2). If BREIT is false, reconstruction takes place in the lab frame. If USECMF is true, the entire event record is boost to the hadron- hadron cmf before event processing, and boosted back afterwards. This means that fixed-target simulation can be done in the lab frame, ie with PBEAM2=0. For hadronic processes with lepton beams, this boosting is always done, regardless of the value of USECMF. The interface to the PDFLIB structure function package is compatible with PDFLIB versions 3 and 4. For version 4, AUTPDF() should be set to the author group as listed in the PDFLIB manual, eg 'MRS', and MODPDF() to the set number in the new convention. For version 3, AUTPDF() should be set to 'MODE', and MODPDF() to the set number in the old convention. The `hard' matrix-element correction adds e+e- and DIS events in regions of phase-space that cannot be filled by the usual parton shower. The `soft' matrix-element correction moves emissions around within the shower phase-space, essentially by matching the HARDEST emission (which is not necessarily the first) to the first-order matrix-element. The quantities from PTMIN onwards control the region of phase space in which events are generated and the importance sampling inside those regions. See section 11 on event weights for further details on these quantities and the use of WGTMAX and NOWGT. If hadronic processes with lepton beams are requested, the photon emission vertex includes the full transverse-momentum-dependent kinematics (the Equivalent Photon Approximation). The variables Q2WWMN and Q2WWMX set the minimum and maximum virtualities generated respectively. For normal simulation, Q2WWMN should be 0, and Q2WWMX should be the largest Q**2 through which the lepton can be scattered without being detected. The variables YBMIN and YBMAX control the range of lightcone momentum fraction generated. In addition there are options to give different weights to the various flavours of quarks and diquarks, and to resonances of different spins. So far, these options have not been used. See the comments in the initialization routine HWIGIN for details. ------------------------------------------------------------------------ ****** 7. COMMON BLOCK FILE ****** C ****COMMON BLOCK FILE FOR HERWIG VERSION 5.9**** C C ALTERATIONS: See 5.8 for list of previous revisions C Layout completely overhauled C C The following variables have been removed: C FBTM,FTOP,FHVY,VECWT,TENWT,SWT,RESWT C MADDR,MODES,MODEF,IDPRO C The following COMMON BLOCK has been removed C /HWUFHV/ - BDECAY moved to /HWPRCH/ C The following COMMON BLOCKs have been added C /HWBMCH/ -contains PART1, PART2 from /HWBEAM/ C /HWPRCH/ -contains AUTPDF from /HWPARM/ & BDECAY C /HWPROP/ -contains many variables from /HWUPDT/ C /HWDIST/ -contains variables for mixing and vertices C /HWQDKS/ -contains heavy flavour decay information C The following variables have been changed to CHARACTER*8: C PART1,PART2,RNAME C The following parameters have been added: C NMXCDK,NMXDKS,NMXMOD,NMXQDK,NMXRES C The following variables have been added: C CSPEED,F0MIX,F1MIX,F2MIX,H1MIX, C PHIMIX,IOPREM,PRVTX see HWPRAM C ANOMSC,ISLENT see HWBRCH C GAMWT see HWEVNT C ASFIXD,OMEGA0,TMNISR,WHMIN,YWWMAX, C YWWMIN,ZMXISR,COLISR see HWHARD C IFLAV,RLTIM,RSPIN,VTOCDK,VTORDK see HWPROP C DKLTM,IDK,IDKPRD,LNEXT,LSTRT, C NDKYS,NME,NMODES,NPRODS, C DKPSET,RSTAB see HWUPDT C REPWT,SNGWT see HWUWTS C CLDKWT,CTHRPW,PRECO,NCLDK,CLRECO see HWUCLU C EXAG,GEV2MM,HBAR,PLTCUT,VMIN2, C VTXPIP,XMIX,XMRCT,YMIX,YMRCT, C IOPDKL,MAXDKL,MIXING,PIPSMR see HWDIST C VTXQDK,IMQDK,LOCQ,NQDK see HWQDKS C C IMPLICIT NONE DOUBLE PRECISION ZERO,ONE,TWO,THREE,FOUR,HALF PARAMETER (ZERO =0.D0, ONE =1.D0, TWO =2.D0, & THREE=3.D0, FOUR=4.D0, HALF=0.5D0) C DOUBLE PRECISION & ACCUR,AFCH,ALPFAC,ALPHEM,ANOMSC,ASFIXD,AVWGT,B1LIM,BETAF,BRFRAC, & BRHIG,BTCLM,CAFAC,CFFAC,CLDKWT,CLMAX,CLPOW,CLQ,CLSMR,CMMOM,COSS, & COSTH,CSPEED,CTHRPW,CTMAX,DECPAR,DECWT,DISF,DKLTM,EBEAM1,EBEAM2, & EMLST,EMMAX,EMMIN,EMPOW,EMSCA,ENHANC,ENSOF,EPOLN,ETAMIX,EVWGT, & EXAG,F0MIX,F1MIX,F2MIX,GAMH,GAMMAX,GAMW,GAMWT,GAMZ,GAMZP,GCOEF, & GEV2NB,GEV2MM,GPOLN,H1MIX,HBAR,HARDST,OMEGA0,PBEAM1,PBEAM2,PDIQK, & PGSMX,PGSPL,PHEP,PHIMIX,PHIPAR,PHOMAS,PIFAC,PLTCUT,PPAR,PPOLN, & PRECO,PRSOF,PSPLT,PTINT,PTMAX,PTMIN,PTPOW,PTRMS,PXRMS,PWT,Q2MAX, & Q2MIN,Q2POW,Q2WWMN,Q2WWMX,QCDL3,QCDL5,QCDLAM,QDIQK,QEV,QFCH,QG, & QLIM,QSPAC,QV,QWT,REPWT,RESN,RHOHEP,RHOPAR,RLTIM,RMASS,RMIN, & RSPIN,SCABI,SINS,SNGWT,SWEIN,SWTEF,SUD,THMAX,TLOUT,TMTOP,TMNISR, & TQWT,VCKM,VFCH,VGCUT,VHEP,VMIN2,VPAR,VPCUT,VQCUT,VTXPIP,VTXQDK, & WBIGST,WGTMAX,WGTSUM,WHMIN,WSQSUM,XFACT,XLMIN,XMIX,XMRCT,XX, & XXMIN,YBMAX,YBMIN,YJMAX,YJMIN,YMIX,YMRCT,YWWMAX,YWWMIN,ZBINM, & ZJMAX,ZMXISR C INTEGER & CLDIR,IAPHIG,IBRN,IBSH,ICHRG,ICO,IDCMF,IDHEP,IDHW,IDK,IDKPRD,IDN, & IDPAR,IDPDG,IERROR,IFLAV,IFLMAX,IFLMIN,IHPRO,IMQDK,INHAD,INTER, & IOPDKL,IOPHIG,IOPREM,IPART1,IPART2,IPRINT,IPRO,IPROC,ISLENT, & ISPAC,ISTAT,ISTHEP,ISTPAR,JCOPAR,JDAHEP,JDAPAR,JMOHEP,JMOPAR, & JNHAD,LNEXT,LOCN,LOCQ,LRSUD,LSTRT,LWEVT,LWSUD,MAPQ,MAXER,MAXEV, & MAXFL,MAXPR,MODBOS,MODMAX,MODPDF,NBTRY,NCLDK,NCOLO,NCTRY,NDKYS, & NDTRY,NETRY,NEVHEP,NEVPAR,NFLAV,NGSPL,NHEP,NME,NMODES,NMXCDK, & NMXDKS,NMXHEP,NMXJET,NMXMOD,NMXPAR,NMXQDK,NMXRES,NMXSUD,NPAR, & NPRODS,NQDK,NQEV,NRES,NRN,NSPAC,NSTRU,NSTRY,NSUD,NUMER,NUMERU, & NWGTS,NZBIN,SUDORD C LOGICAL & AZSOFT,AZSPIN,BGSHAT,BREIT,CLRECO,COLISR,DKPSET,FROST,FSTEVT, & FSTWGT,GENEV,GENSOF,HARDME,HVFCEN,MAXDKL,MIXING,NOSPAC,NOWGT, & PRNDEC,PIPSMR,PRVTX,RSTAB,SOFTME,TMPAR,TPOL,USECMF,VTOCDK,VTORDK, & ZPRIME C CHARACTER*4 & BDECAY CHARACTER*8 & PART1,PART2,RNAME CHARACTER*20 & AUTPDF C C New standard event common PARAMETER (NMXHEP=2000) COMMON/HEPEVT/NEVHEP,NHEP,ISTHEP(NMXHEP),IDHEP(NMXHEP), & JMOHEP(2,NMXHEP),JDAHEP(2,NMXHEP),PHEP(5,NMXHEP),VHEP(4,NMXHEP) C C Beams, process and number of events COMMON/HWBEAM/IPART1,IPART2 COMMON/HWBMCH/PART1,PART2 COMMON/HWPROC/EBEAM1,EBEAM2,PBEAM1,PBEAM2,IPROC,MAXEV C C Basic parameters (and quantities derived from them) COMMON/HWPRAM/AFCH(16,2),ALPHEM,B1LIM,BETAF,BTCLM,CAFAC,CFFAC, & CLMAX,CLPOW,CLSMR,CSPEED,ENSOF,ETAMIX,F0MIX,F1MIX,F2MIX,GAMH, & GAMW,GAMZ,GAMZP,GEV2NB,H1MIX,PDIQK,PGSMX,PGSPL(4),PHIMIX,PIFAC, & PRSOF,PSPLT,PTRMS,PXRMS,QCDL3,QCDL5,QCDLAM,QDIQK,QFCH(16),QG, & QSPAC,QV,SCABI,SWEIN,TMTOP,VFCH(16,2),VCKM(3,3),VGCUT,VQCUT, & VPCUT,ZBINM,IOPREM,IPRINT,ISPAC,LRSUD,LWSUD,MODPDF(2),NBTRY, & NCOLO,NCTRY,NDTRY,NETRY,NFLAV,NGSPL,NSTRU,NSTRY,NZBIN,AZSOFT, & AZSPIN,CLDIR,HARDME,NOSPAC,PRNDEC,PRVTX,SOFTME,ZPRIME C COMMON/HWPRCH/AUTPDF(2),BDECAY C C Parton shower common (same format as /HEPEVT/) PARAMETER (NMXPAR=500) COMMON/HWPART/NEVPAR,NPAR,ISTPAR(NMXPAR),IDPAR(NMXPAR), & JMOPAR(2,NMXPAR),JDAPAR(2,NMXPAR),PPAR(5,NMXPAR),VPAR(4,NMXPAR) C C Parton polarization common COMMON/HWPARP/DECPAR(2,NMXPAR),PHIPAR(2,NMXPAR),RHOPAR(2,NMXPAR), & TMPAR(NMXPAR) C C Electroweak boson common PARAMETER (MODMAX=5) COMMON/HWBOSC/ALPFAC,BRHIG(12),ENHANC(12),GAMMAX,RHOHEP(3,NMXHEP), & IOPHIG,MODBOS(MODMAX) C C Parton colour common COMMON/HWPARC/JCOPAR(4,NMXPAR) C C other HERWIG branching, event and hard subprocess common blocks COMMON/HWBRCH/ANOMSC(2,2),HARDST,PTINT(3,2),XFACT,INHAD,JNHAD, & NSPAC(7),ISLENT,BREIT,FROST,USECMF C COMMON/HWEVNT/AVWGT,EVWGT,GAMWT,TLOUT,WBIGST,WGTMAX,WGTSUM,WSQSUM, & IDHW(NMXHEP),IERROR,ISTAT,LWEVT,MAXER,MAXPR,NOWGT,NRN(2),NUMER, & NUMERU,NWGTS,GENSOF C COMMON/HWHARD/ASFIXD,CLQ(7,6),COSS,COSTH,CTMAX,DISF(13,2),EMLST, & EMMAX,EMMIN,EMPOW,EMSCA,EPOLN(3),GCOEF(7),GPOLN,OMEGA0,PHOMAS, & PPOLN(3),PTMAX,PTMIN,PTPOW,Q2MAX,Q2MIN,Q2POW,Q2WWMN,Q2WWMX,QLIM, & SINS,THMAX,TMNISR,TQWT,XX(2),XLMIN,XXMIN,YBMAX,YBMIN,YJMAX, & YJMIN,YWWMAX,YWWMIN,WHMIN,ZJMAX,ZMXISR,IAPHIG,IBRN(2),IBSH, & ICO(10),IDCMF,IDN(10),IFLMAX,IFLMIN,IHPRO,IPRO,MAPQ(6),MAXFL, & BGSHAT,COLISR,FSTEVT,FSTWGT,GENEV,HVFCEN,TPOL C C Arrays for particle properties (NMXRES = max no of particles defined) PARAMETER(NMXRES=400) COMMON/HWPROP/RLTIM(0:NMXRES),RMASS(0:NMXRES),RSPIN(0:NMXRES), & ICHRG(0:NMXRES),IDPDG(0:NMXRES),IFLAV(0:NMXRES),NRES, & VTOCDK(0:NMXRES),VTORDK(0:NMXRES) C COMMON/HWUNAM/RNAME(0:NMXRES) C C Arrays for particle decays (NMXDKS = max total no of decays, C NMXMOD = max no of modes for a particle) PARAMETER(NMXDKS=4000,NMXMOD=200) COMMON/HWUPDT/BRFRAC(NMXDKS),CMMOM(NMXDKS),DKLTM(NMXRES), & IDK(NMXDKS),IDKPRD(5,NMXDKS),LNEXT(NMXDKS),LSTRT(NMXRES),NDKYS, & NME(NMXDKS),NMODES(NMXRES),NPRODS(NMXDKS),DKPSET,RSTAB(0:NMXRES) C C Weights used in cluster decays COMMON/HWUWTS/REPWT(0:3,0:4,0:4),SNGWT,DECWT,QWT(3),PWT(12), & SWTEF(NMXRES) C C Parameters for cluster decays (NMXCDK = max total no of cluster C decay channels) PARAMETER(NMXCDK=4000) COMMON/HWUCLU/CLDKWT(NMXCDK),CTHRPW(12,12),PRECO,RESN(12,12), & RMIN(12,12),LOCN(12,12),NCLDK(NMXCDK),CLRECO C C Variables controling mixing and vertex information COMMON/HWDIST/EXAG,GEV2MM,HBAR,PLTCUT,VMIN2,VTXPIP(4),XMIX(2), & XMRCT(2),YMIX(2),YMRCT(2),IOPDKL,MAXDKL,MIXING,PIPSMR C C Arrays for temporarily storing heavy-b,c-hadrons decaying partonicaly C (NMXBDK = max no such b-hadron decays in an event) PARAMETER (NMXQDK=20) COMMON/HWQDKS/VTXQDK(4,NMXQDK),IMQDK(NMXQDK),LOCQ(NMXQDK),NQDK C C Parameters for Sudakov form factors C (NMXSUD= max no of entries in lookup table) PARAMETER (NMXSUD=1024) COMMON/HWUSUD/ACCUR,QEV(NMXSUD,6),SUD(NMXSUD,6),INTER,NQEV,NSUD, & SUDORD C PARAMETER (NMXJET=200) ------------------------------------------------------------------------ ****** 8. FORM FACTOR FILE ****** HERWIG uses look-up tables of Sudakov form factors for the evolution of initial- and final-state parton showers. These can be read from an input file rather than being recomputed each time. The reading, writing and computing of form factor tables is controlled by integer parameters LRSUD and LWSUD: LRSUD = N>0 Read form factors for this run from unit N LRSUD = 0 Compute new form factor tables for this run LRSUD < 0 Form factor tables are already loaded LWSUD = N>0 Write form factors on unit N for future use LWSUD = 0 Do not write new form factor tables The option LRSUD<0 allows the program to be initialized several times in the same run (e.g. to generate various event types) without recom- puting or rereading form factors. N.B. The Sudakov form factors depend on the parameters QCDLAM, VQCUT, VGCUT, NCOLO, NFLAV, NAFLA, RMASS(13) and RMASS(i) for i=1,...,NFLAV. Consequently form factor tables MUST be recomputed every time any of these parameters is changed. From version 5.1 onwards, these parameters are written/read with the form factor tables and checks are performed to ensure consistency. The parton showering algorithm uses the two-loop alpha_s, with matching at each flavour threshold. However, the Sudakov table can be computed with either the one-loop or two-loop form, according to the variable SUDORD (= 1 or 2 respectively, DEFAULT=1). If SUDORD=1 the two-loop value is recovered using the veto algorithm in the shower, whereas if SUDORD=2 no vetoes are used in the final-state evolution. This means that the relative weight of any shower configuration can be calculated in a closed form, hence that showers can be `forced'. To next-to-leading order the two possibilities should be identical, but they differ at beyond-NLO, so some results may change a little. The most noticeable difference is that the form factor table takes a factor of about five times longer to compute with SUDORD=2 than 1. ------------------------------------------------------------------------ ****** 9. EVENT DATA ****** /HEPEVT/ is the standard common block containing current event data: NEVHEP - event number NHEP - number of entries for this event ISTHEP(I) - status of entry I (see below) IDHEP(I) - identity of entry I (revised Particle Data Group code) JMOHEP(1,I) - pointer to first mother of entry I (see below) JMOHEP(2,I) - pointer to second mother of entry I (see below) JDAHEP(1,I) - pointer to first daughter of entry I (see below) JDAHEP(2,I) - pointer to last daughter of entry I (see below) PHEP(*,I) - (Px,Py,Pz,E,M) of entry I: M=sign(sqrt(abs(m**2)),m**2) VHEP(*,I) - (x,y,z,t) of prod'n vertex of entry I (see section 13) All momenta are given in the laboratory frame, in which the input beam momenta are PBEAM1 and PBEAM2 as specified by the user and point along the +z and -z directions respectively. Final state particles have ISTHEP(I) = 1. See the next section for a complete list of the special status codes used by HERWIG. The identity codes IDHEP are as those suggested by the LEP II Working group i.e. the revised Particle Data Group numbers plus the following * IDHEP = 91 for clusters, 94 for jets, 0 for others with no PDG code. (HERWIG also has its own internal identity codes IDHW(I), stored in /HWEVNT/. The utility subroutine HWUIDT translates between HERWIG and PDG identity codes. See section 20 for further details.) The mother/daughter pointers are standard, except that JMOHEP(2,I) and JDAHEP(2,I) for a PARTON are its COLOUR mother and daughter, i.e., the partons to which its colour and anticolour are connected, respectively. For this purpose the primary partons from a hard sub- process are all regarded as outgoing (see examples in sects. 15, 19 and 21). Since quarks have no anticolour, JDAHEP(2,I) is used to point to its FLAVOUR partner. Similarly for JMOHEP(2,I) in the case of an antiquark. In addition to entries representing partons, particles, clusters etc, /HEPEVT/ contains purely informational entries representing the total c.m. momentum, hard and soft subprocess momenta, etc. See section 10 for the corresponding status codes. Information from all stages of event processing is retained in /HEPEVT/ so the same particle may appear several times with different status codes. For example, an outgoing parton from a hard scattering (entered initially with status 113 or 114) will appear after process- ing as an on-mass-shell parton before QCD branching (status 123,124), an off-mass-shell entry representing the flavour and momentum of the outgoing jet (status 143,144), and a jet constituent (157). It might also appear again in other contexts, e.g. as a spectator in a heavy flavour decay (status 154,160). Incoming partons (entered with status 111, 112, changed to 121, 122 after branching) give rise to spacelike jets (status 141,142, m**2<0, indicated by PHEP(5,IHEP)<0) due to the loss of momentum via initial state bremsstrahlung. The same applies in principle to incoming leptons, but QED radiative corrections are not yet included. Each parton jet begins with a status 141-144 jet entry giving the total flavour and momentum of the jet. The first mother pointer of this entry gives the location of the parent hard parton, while the second gives that of the subprocess c.m. momentum. If QCD branching has occurred, this is followed by a lightlike CONE entry, which fixes the angular extent of the jet and its azimuthal orientation relative to the parton with which it interferes. The interfering par- ton is listed as the second mother of the cone. Next come the actual constituents of the jet. If no branching has occurred, there is no cone and the single jet constituent is the same as the jet. ------------------------------------------------------------------------ ****** 10. STATUS CODES ****** A complete list of currently-used HERWIG status codes is given below. Many are used only in intermediate stages of event processing. The most important for users are probably 1 (final-state particle), 101-3 (initial state), 141-4 (jets), and 199 (decayed b- and t-flavoured hadrons). The event status ISTAT in common /HWEVNT/ is roughly ISTHEP-100 where ISTHEP is the status of entries being processed. However, ISTAT=100 for completed events. +------+-------------------------------------------+ |ISTHEP| Description | +------+-------------------------------------------+ | 1 | final state particle | | 2 | parton before hadronization | | 3 | documentation line | +------+-------------------------------------------+ | 100 | cone limiting jet evolution | | 101 | `beam' (beam 1) | | 102 | `target' (beam 2) | | 103 | overall centre of mass | +------+-------------------------------------------+ | 110 | unprocessed hard process CoM | | 111 | " beam parton | | 112 | " target " | | 113 | " outgoing " 3 | | 114 | " outgoing " 4 | | 115 | " spectator " | +------+-------------------------------------------+ |120-25| as 110-15, after processing | +------+-------------------------------------------+ | 130 | lepton in jet (unboosted) | |131-34| as 141-44, unboosted to CoM | | 135 | spacelike parton (beam, unboosted) | | 136 | " " (target, " ) | | 137 | spectator (beam, unboosted) | | 138 | " (target, " ) | | 139 | parton from branching (unboosted) | | 140 | " " g splitting ( " ) | +------+-------------------------------------------+ |141-44| jet from parton type 111-14 | |145-50| as 135-40 boosted, unclustered | +------+-------------------------------------------+ | 151 | as 159, not yet clustered | | 152 | as 160, " " " | | 153 | spectator from beam | | 154 | " " target | | 155 | heavy quark before decay | | 156 | spectator before heavy decay | | 157 | parton from QCD branching | | 158 | " after gluon splitting | | 159 | " from cluster splitting | | 160 | spectator after heavy decay | +------+-------------------------------------------+ | 161 | beam spectator after gluon splitting | | 162 | target " " " " | | 163 | other cluster before soft process | | 164 | beam " " " " | | 165 | target " " " " | | 167 | unhadronized beam cluster | | 168 | unhadronized target cluster | +------+-------------------------------------------+ | 170 | soft process centre of mass | | 171 | soft cluster (beam, unhadronized) | | 172 | soft cluster (target, " ) | | 173 | soft cluster (other, " ) | +------+-------------------------------------------+ | 181 | beam cluster (no soft process) | | 182 | target " ( " " " ) | | 183 | hard process " (hadronized) | | 184 | soft " (beam, hadronized) | | 185 | " " (target, " ) | | 186 | " " (other, " ) | +------+-------------------------------------------+ |190-93| as 195-98, before decays | | 195 | direct unstable non-hadron | | 196 | " " hadron (1-body cluster) | | 197 | " " " (2-body cluster) | | 198 | indirect unstable hadron or lepton | | 199 | decayed heavy flavour hadron | +------+-------------------------------------------+ | 200 | neutral B meson, flavour at production | +------+-------------------------------------------+ ------------------------------------------------------------------------ ****** 11. EVENT WEIGHTS ****** The default is to generate unweighted events (EVWGT=AVWGT). Then event distributions are generated by computing a weight proportional to the cross section and comparing it with a random number times the maximum weight. Set WGTMAX to the maximum weight, or to zero for the program to compute it. If a weight greater than WGTMAX is generated during execution, a warning is printed and WGTMAX is reset. Similarly if the efficiency is too low (WGTMAX too large). If these errors occur too often, output event distributions could be distorted. To generate weighted events, set NOWGT=.FALSE. in common /HWEVNT/. In QCD hard scattering and heavy flavour and direct photon production (IPROC = 1500 to 1800) the transverse energy distribution of weighted events (or the efficiency for unweighted events) can be varied using the parameters PTMIN, PTMAX and PTPOW. Similarly in Drell-Yan processes (IPROC = 13**) the lepton pair mass distribution is controlled by the parameters EMMIN, EMMAX and EMPOW, and in deep inelastic scattering the Q**2 distribution is set by Q2MIN, Q2MAX and Q2POW. Data on weights generated are output at the end of the run. The mean weight is an estimate of the cross section (in nanobarns) integrated over the region used for event generation. N.B. The mean weight is the sum of weights divided by the total number of WEIGHTS generated, not the total number of EVENTS. ------------------------------------------------------------------------ ****** 12. HEAVY FLAVOUR DECAYS ****** Heavy quark decays are treated as secondary hard subprocesses. Top quarks can decay either before or after hadronization, depending on the value of the logical variable DECAY returned by the subroutine HWDTOP. At present decay occurs before hadronization (DECAY=.TRUE.) if the top mass is above 130 GeV (default=170 GeV). Any hypothetical heavier quarks always decay before hadronization. Top- and bottom- flavoured hadrons are split into collinear heavy quark and spectator and the former decays independently. After decay, parton showers may be generated from coloured decay products, in the usual way. See Nucl. Phys. B330 (1990) 261 for details of the treatment of colour coherence in these showers. The arrays FBTM, FTOP & FHVY which were used in versions before 5.9 to store the bottom, top & heavier quarks' partonic decay fractions are gone. Such decays are specified in the decay tables like other particles' decay modes: this permits different decays to be given to individual heavy hadrons. Changes to the decay table entries can be made on an event by event basis if desired. Partonic decays of charm hadrons and quarkonium states are also now supported. The products' order in a partonic decay mode is significant. For example, if the decay is Q --> W+q --> (f+fbar')+q occurring inside a Q-sbar hadron, the required ordering is: Q+sbar --->(f+fbar')+(q+sbar) or (q+fbar')+(f+sbar) `colour rearranged' In both cases the (V-A)^2 ME^2 is proportional to: p_0.p_2 * p_1*p_3 The structure of the program has been altered so that secondary hard subrocess and subsequent fragmentation associated with each partonic heavy hadron decay appear separately. Thus pre-hadronization t quark decays are treated individually as are any subsequent bottom hadron partonic decays. Additionally decays of heavy hadrons to exclusive non-partonic final states are supported. No check against double counting from partonic modes is included. However this isn't expected to be a major problem for the semi-leptonic and 2-body hadronic modes supplied. ------------------------------------------------------------------------ ****** 13. SPACE-TIME STRUCTURE OF EVENTS ****** The space-time structure of events is now available for all types of subprocess. The production vertex of each: parton, cluster, unstable resonance and final state particle is supplied in the VHEP(4,NMXHEP) array of /HEPEVT/; set PRVTX=.TRUE. to include this information when printing the event record (120 column format). The units are: x,y,z in mm and t mm/c. In the case of partons and clusters the production points are always given in a loacl coordinate system centered on the their hard sub-process. This helps seperate the fermi scale partonic showers from millimeter scale distances possible in particle decays, for example the partonic decays of heavy (c,b) hadrons. The vertices of hadrons produced in cluster decays are always corrected back into the laboratory coordinate system. It is possible to vary the principal interaction point, assigned to the CMF (ISTHEP=103) track, by setting PIPSMR=.TRUE. The smearing is generated by the routine HWRPIP according to a triple Gaussian, see the code for details. Also, it is possible to veto particle decays that would occur outside a specified volume by setting MAXDKL=.TRUE. Each putative decay is tested in HWDXLM and if it would have decayed outside the chosen volume it is frozen and labelled as final state. Using IOPDKL = 1,2 selects a cylindrical or spherical allowed region (about the origin) see the code for details. Lepton and hadron lifetimes are supplied in the array RLTIM(NMXRES). The lifetimes of heavy quarks (TQRK, VQRK, AQRK, HQRK AND HPQK), and weak bosons (W+, W-, Z0/GAMA*, HIGGS and Z0P) are derived from their calculated or specified widths as calculated in HWUDKS, whilst light quarks and gluons are given an effective minimum width, sqrt(VMIN2), that acts as a lifetime cut-off - see below. Recall that the proper lifetime = HBAR/Gamma. All particles whose lifetimes are larger than PLTCUT are set stable. The proper (= rest frame) time at which an unstable lepton or hadron decays is generated according to the exponential decay law with mean lifetime =RLTIM. The laboratory frame decay time and distance travelled are obtained by applying a boost: Rest Prob (proper time < t) = 1 * exp(-t/) frame Lab. time = gamma * proper time beta = v/c frame dist = beta * gamma * proper time gamma = 1/sqrt(1-beta^2) The production vertices of the daughter particles are calculated by adding the distance travelled by the mother particle as given above to its production vertex. A similar prescription is used for parton showers: proper lifetimes are taken from an exponential distribution with a virtuality dependent mean lifetime 1/HBAR*sqrt(q^2/(q^2-m^2)) inspired by the uncertainty relationship: mean lifetimes are limited by a cut-off on the minimum virtuality VMIN2. The mean lifetimes of heavy quarks and weak bosons, which can have appreciable widths, are given by: hbar.sqrt(q^2) (q^2) = ----------------------------- \/(q^2-M^2)^2 + (Gamma.q^2/M)^2 As this formula has the appropriate limits for vanishing virtuality, q^2=m^2, or width, gamma=0, it is actually also used in the hadronic and partonic showers: see HWUDKL. In the case of cluster the initial production vertex is taken as the midpoint of a line perpendicular to the cluster's direction and with pair. If such a cluster undergoes a forced splitting to two clusters the string picture is adopted. The vertex of the light quark pair is positioned so that the masses of the two daughter clusters would be the same as that for two equivalent string fragments. The production vertices of the daughter clusters are given by the first crossing of their constituent q-qbar pairs. This part of the space-time picture is admittedly ad hoc however no physics depends upon it. When MIXING=.TRUE. particle - antiparticle mixing for B^0_d,s mesons is implimented. The probability that a meson is mixed when it decays is given in terms of its lab-frame decay time by: 1 sin(X*m*t/cE) X=Delta-M Y=Delta-Gamma Prob(mix) = - + ---------------------- ------- ----------- 2 2 *cosh(Y*m*t/cE) Gamma 2 * Gamma The ratios X and Y are stored in XMIX(I) & YMIX(I), I=1,2 for q=s,d. Whenever a neutral B meson occurs in an event a copy of the original track is always added to the event record, with ISTHEP=200, it gives the particle's flavour at the production (cluster decay) time. This is in addition to the usual decaying particle, ISTHEP=19*, track. ------------------------------------------------------------------------ ****** 14. COLOUR REARRANGEMENT MODEL ****** HERWIG now contains a colour rearrangement model based on the space- time structure of an event occuring at the end of the parton shower. This is illustrated in the simple example shown below where a colour neutral source results in a q-g-g-qbar shower. In the conventional hadronization model after a nonperturbative splitting of final state gluons - Wolfram ansatze - colour singlet clusters are formed from neighbouring q-qbar pairs: (ij)(pq)(kl). However when CLRECO=.TRUE. the program first creates colour singlet clusters as normal but then checks all (non-neighbouring) pairs of clusters to test if a colour rearrangement lowers the sum of the clusters' spatial sizes added in quadrature. A cluster's size is defined to be the Lorentz invariant, space-time distance between the constituent quark's and anitquark's production points. If an allowed alternative is found, that is: (ij)(kl) --> (il)(jk) s.t. (|d_ij|^2+|d_kl|^2) > (|d_il|^2+|d_kl|^2) then it is accepted with a probability given by PRECO (default 1/9). ____ i Normal: (ij) (pq) (kl) / /____/ j If: ------ / \ p |d_ij|^2+|d_kl|^2 > |d_il|^2+|d_kl|^2 ------| \______/ q colour rearr.: (il) (pq) (jk) ----- \ \ k Not allowed: (iq) (jp) (kl) \ ^ ---- l | colour octet Note that not all colour rearrangements are allowed, for instance in the example (ij)(pq) --> (ip)(jq) the cluster (jq) is a colour octet - it contains both products from a non-perturbative gluon splitting. Multiple colour rearrangements are considered by the program, as are those between clusters in jets arising from a single, colour neutral source - for example Z0 decay (as shown above) - or due to more than one source - for example e+e- --> W+W- --> 4 jets. In the later case a new parameter, EXAG, is available to artificially scale the W - or other weak boson - lifetimes so that any dependence of rearrangement effects on source separation can be investigated. The CLRECO option can be used for all the processes available in HERWIG. ** NOTE ** Before using the program with CLRECO=.TRUE. for detailed physics analyses the default parameters should be retuned to `lower energy' data with this option switched on. ------------------------------------------------------------------------ ****** 15. QCD HARD SUBPROCESSES ****** At present only 2->2 subprocesses are implemented. They are class- ified as shown below. +-----+------------------------------+---------+ |IHPRO| Process 1 + 2 -> 3 + 4 |Col/F.Con| +-----+------------------------------+---------+ | 1 | q + q -> q + q | 3 4 2 1 | | 2 | q + q -> q + q | 4 3 1 2 | | 3 | q + q' -> q + q' | 3 4 2 1 | | 4 | q + qbar -> q'+ qbar' | 2 4 1 3 | | 5 | q + qbar -> q + qbar | 3 1 4 2 | | 6 | q + qbar -> q + qbar | 2 4 1 3 | | 7 | q + qbar -> g + g | 2 4 1 3 | | 8 | q + qbar -> g + g | 2 3 4 1 | | 9 | q + qbar' -> q + qbar' | 3 1 4 2 | | 10 | q + g -> q + g | 3 1 4 2 | | 11 | q + g -> q + g | 3 4 2 1 | | 12 | qbar + q -> qbar' +q' | 3 1 4 2 | | 13 | qbar + q -> qbar + q | 2 4 1 3 | | 14 | qbar + q -> qbar + q | 3 1 4 2 | | 15 | qbar + q -> g + g | 3 1 4 2 | | 16 | qbar + q -> g + g | 4 1 2 3 | | 17 | qbar + q' -> qbar + q' | 2 4 1 3 | | 18 | qbar + qbar -> qbar + qbar | 4 3 1 2 | | 19 | qbar + qbar -> qbar + qbar | 3 4 2 1 | | 20 | qbar + qbar' -> qbar + qbar' | 4 3 1 2 | | 21 | qbar + g -> qbar + g | 2 4 1 3 | | 22 | qbar + g -> qbar + g | 4 3 1 2 | | 23 | g + q -> g + q | 2 4 1 3 | | 24 | g + q -> g + q | 3 4 2 1 | | 25 | g + qbar -> g + qbar | 3 1 4 2 | | 26 | g + qbar -> g + qbar | 4 3 1 2 | | 27 | g + g -> q + qbar | 2 4 1 3 | | 28 | g + g -> q + qbar | 4 1 2 3 | | 29 | g + g -> g + g | 4 1 2 3 | | 30 | g + g -> g + g | 4 3 1 2 | | 31 | g + g -> g + g | 2 4 1 3 | +-----+------------------------------+---------+ `Col/F.Con' refers to the colour/flavour connections between the partons:`I J K L' means that the colour of parton 1 comes from parton I, that of 2 from J, etc. For antiquarks, which have no colour (only anticolour), the label shows instead to which parton the flavour is connected. For this colour/flavour labelling all partons are defined as outgoing. Thus, for example, process 10 has colour connections 3 1 4 2, corresponding to the colour flow diagram: 1 -->--+ +-->-- 3 | | | | --<--+ +--<-- 2 -->------->-- 4 When different colour flows are possible, they are listed as separate subprocesses. This separation is not exact but is normally a good approximation. The sum of the colour flows is the exact lowest-order cross section. ------------------------------------------------------------------------ ****** 16. QCD DIRECT PHOTON SUBPROCESSES ****** +-----+------------------------------+---------+ |IHPRO| Process 1 + 2 -> 3 + 4 |Col/F.Con| +-----+------------------------------+---------+ | 41 | q + qbar -> g + photon | 2 3 1 4 | | 42 | q + gluon -> q + photon | 3 1 2 4 | | 43 | qbar + q -> g + photon | 3 1 2 4 | | 44 | qbar + gluon -> qbar + photon| 2 3 1 4 | | 45 | gluon + q -> q + photon| 2 3 1 4 | | 46 | gluon + qbar -> qbar + photon| 3 1 2 4 | | 47 | gluon + gluon-> gluon+ photon| 2 3 1 4 | +-----+------------------------------+---------+ | 51 | photon+ q -> gluon+ q | 1 4 2 3 | | 52 | photon+ qbar -> gluon+ qbar | 1 3 4 2 | | 53 | photon+ gluon-> q + qbar | 1 4 2 3 | +-----+------------------------------+---------+ | 61 | q + qbar -> photon+photon| 2 1 3 4 | | 62 | qbar + q -> photon+photon| 2 1 3 4 | | 63 | gluon + gluon-> photon+photon| 2 1 3 4 | +-----+------------------------------+---------+ | 71 | photon+ q -> M(S=0) +q' | 1 4 3 2 | | 72 | photon+ q -> M(S=1)L+q' | 1 4 3 2 | | 73 | photon+ q -> M(S=1)T+q' | 1 4 3 2 | | 74 | photon+ qbar -> M(S=0) +qbar'| 1 4 3 2 | | 75 | photon+ qbar -> M(S=1)L+qbar'| 1 4 3 2 | | 76 | photon+ qbar -> M(S=1)T+qbar'| 1 4 3 2 | +-----+------------------------------+---------+ N.B. The photon is connected to itself. ------------------------------------------------------------------------ ****** 17. QCD HIGGS PLUS JET SUBPROCESSES ****** +-----+------------------------------+---------+ |IHPRO| Process 1 + 2 -> 3 + 4 |Col/F.Con| +-----+------------------------------+---------+ | 81 | q + qbar -> g + H | 2 3 1 4 | | 82 | q + g -> q + H | 3 1 2 4 | | 83 | qbar + q -> g + H | 3 1 2 4 | | 84 | qbar + g -> qbar + H | 2 3 1 4 | | 85 | g + q -> q + H | 2 3 1 4 | | 86 | g + qbar -> qbar + H | 3 1 2 4 | | 87 | g + g -> g + H | 2 3 1 4 | +-----+------------------------------+---------+ N.B. The Higgs is connected to itself. ------------------------------------------------------------------------ ****** 18. ELECTROWEAK SUBPROCESSES ****** HERWIG generates Higgs bosons through gluon-gluon/quark-antiquark fusion, and W fusion in hadron-hadron collisions (IPROC=1600+ID and 1900+ID), in lepton-lepton collisions through the Bjorken process (that is, Z(*)->Z(*)H with one or both Zs off-shell) and W fusion (IPROC=300+ID and 400+ID), and in lepton-hadron collisions through W fusion (IPROC=9500+ID). Each process is generated according to the exact leading order matrix element in the s-channel approximation. This results in unitarity violation for Mh >> Mw, s >~ a few Mh^2, (where s=qh^2), so to regularize this, the Mh*GAMH in the propagator can be replaced by SQRT(s)*GAMH(s). The variable IOPHIG controls this procedure: +------+------------------------------+-----------+ |IOPHIG| Choose s according to | Reweight? | +------+------------------------------+-----------+ | 0 | s^2 / ((s-Mh^2)^2 + Mh*GAMH) | YES | | 1 | 1 / ((s-Mh^2)^2 + Mh*GAMH) | YES | | 2 | s^2 / ((s-Mh^2)^2 + Mh*GAMH) | NO | | 3 | 1 / ((s-Mh^2)^2 + Mh*GAMH) | NO | +------+------------------------------+-----------+ Where reweighting means weighting the distribution back to SQRT(s) * GAMH(s) ---------------------------- (s-Mh^2)^2 + SQRT(s)*GAMH(s) The default is IOPHIG=1. The difference between options 0 and 1 is purely in the weight distribution produced. Options 2 and 3 are intended primarily for users who wish to supply their own unitarity conserving reweighting function at the point indicated in routine HWHIGM. In all cases, the distribution is restricted to the range [Mh-GAMMAX*GAMH , Mh+GAMMAX*GAMH]. GAMMAX defaults to 10, but in the (probably unphysical) region Mh >~ 1TeV should be reduced to protect against poor weight distributions. These considerations do not affect the distribution noticably for Mh <~ 500 GeV, and GAMMAX can safely be increased if necessary. For each process, ID controls the Higgs decay: ID=1-6 for quarks, 7-9 for leptons, 10/11 for WW/ZZ pairs, and 12 for photons. In addition ID=0 gives quarks of all flavours, and ID=99 gives all decays. For each process, the average event weight is the cross section in nb times the branching fraction to the requested decay. The branching ratios to quarks use the next-to-leading logarithm corrections, those to WW/ZZ pairs allow for one or both bosons off-shell. The amplitudes for all Higgs vertices are multiplied by the factor ENHANC(ID) where ID is the same as in IPROC=300+ID except the gammagammaHiggs `vertex' which is calculated from ENHANC(6) and ENHANC(10) for the top and W loops. This allows the simulation of any chargeless scalar Higgs. Note however that pseudoscalar and charged Higgses, and processes involving more than one Higgs (eg the decay H-->hZ) are not included. Gauge bosons are generated through the processes of W + 1 parton production in hadron-hadron collisions, and WW pair production in lepton-lepton collisions, as well as in the Higgs processes mentioned above. In all cases their decay is controlled by the variable MODBOS(i). This controls the decay of the ith gauge boson per event: +---------+-----------------+-----------------+ |MODBOS(i)| W Decay | Z Decay | +---------+-----------------+-----------------+ | 0 | all | all | | 1 | qqbar | qqbar | | 2 | enu | e+e- | | 3 | munu | mu+mu- | | 4 | taunu | tau+tau- | | 5 | enu & munu | ee & mumu | | 6 | all | nunu | | 7 | all | bbbar | | >7 | all | all | +---------+-----------------+-----------------+ All entries of MODBOS default to 0. Bosons which are produced in pairs (ie. from WW pair production, or Higgs decay) are symmetrized in MODBOS(i) and MODBOS(i+1). For processes which directly produce gauge bosons, the event weight includes the branching fraction to the requested decay, but this is only true for Higgs production if decay to WW/ZZ is forced (ID=10/11) and not if ID=99. The spin-correlations in the decays are handled in one of two ways: (a) the diagonal members of the spin density matrix are stored in RHOHEP(i,IHEP), where i=1,2,3 for helicity=i-2 in the centre-of- mass frame of their production, for processes where this matrix is diagonal (ie. there is no interference between spin states). (b) the correlations in the decay are handled directly by the production routine where (a) is not possible. In the case of gamma gamma --> W W the decay correlations are not correctly included: they currently decay isotropically. The electroweak vector boson--fermion coupling constants are stored in the arrays QFCH(I), VFCH(I,J) and AFCH(I,J) for the charge, vector and axial vector couplings to the neutral current respectively. These are given in the convention V_f=(T_3/2-Qsin^2_W)/(cos_W sin_W); A_f=T_3/(2 cos_W sin_W). In each case, I= 1- 6: d,u,s,c,b,t (quarks) =11-16: e,nu_e,mu,nu_mu,tau,nu_tau (leptons) (`I=IDHW-110') J=1 for minimal SM: =2 for Z' couplings (only included if ZPRIME=.TRUE.) Note that no universality is assumed -- couplings can be arbitrarily set for each fermion species separately. The quark mixing matrix is stored in VCKM(K,L), K=1,2,3 for u,c,t, L=1,2,3 for d,s,b. A running electromagnetic coupling constant is provided, HWUAEM(Q2). ALPHEM =1/137 provides the normalisation at the Thomson (Q2=0) limit and is used for all processes involving real photons. The electroweak coupling is calculated as, g^2 = 4 PIFAC ALPHEM(Q2) / SWEIN, where Q2 is appropriate for the given process. Photon emission in parton showers, and in the `dead-zone' in e+e- is enhanced by a factor of ALPFAC (default=1.). ------------------------------------------------------------------------ ****** 19. INCLUDING NEW SUBPROCESSES ****** It should not be difficult for users to include further subprocesses in this version of the program if required. The parton and hard sub- process 4-momenta, masses and identity codes need to be entered in COMMON/HEPEVT/ with the appropriate status codes ISTHEP(I)=110-114 to tell the program which is which (see table in sect. 10). The colour/ flavour structure should be specified by the second mother and daugh- ter pointers as explained in section 9 (see also the sample output and guide, sections. 20 and 21). Apart from the status codes ISTHEP, the HERWIG identity codes IDHW(I) in COMMON/HWEVNT/ also need to be set correctly. The IDHW codes can be listed in a run with IPRINT=2: the most important are the quarks 1-6 (as IDHEP), antiquarks 7-12, gluon 13, overall c.m. 14, hard c.m. 15, soft c.m. 16, photon 59, leptons 121-126, antileptons 127-132. The utility subroutine HWUIDT(IOPT,IPDG,IHWG,NAME) is provided to translate between Particle Data Group code IPDG, HERWIG code IHWG, and HERWIG character*8 NAME, with IOPT=1,2,3 depending on which of IPDG, IHWG and NAME is the input argument. Consider for example the process of virtual photon-gluon fusion to make b+bbar in e p collisions. **** N.B. This process is now included as IPROC = 9102 **** We assume the user provides a subroutine to generate the momenta PHEP for the hard subprocess e+g -> e+b+bbar. The colour structure is (e)4 ........... 7(e) : : +-->-- 8(b) | -->--+ (g)5 --<-----<-- 9(bbar) Thus the momenta generated, together with those of the initial beams and the overall centre of mass, could be entered in the following sequence: +----+--------+------+-----+------+------+----+ |IHEP| Entry |ISTHEP|IDHEP|JMOHEP|JDAHEP|IDHW| +----+--------+------+-----+------+------+----+ | 1 | e beam | 101 | 11| 0 0| 0 0| 121| | 2 | p beam | 102 | 2212| 0 0| 0 0| 73| | 3 | ep c.m.| 103 | 0| 0 0| 0 0| 14| +----+--------+------+-----+------+------+----+ | 4 | e in | 111 | 11| 6 7| 0 7| 121| | 5 | gluon | 112 | 21| 6 9| 0 8| 13| | 6 | hard cm| 110 | 0| 4 5| 7 9| 15| | 7 | e out | 113 | 11| 6 4| 0 4| 121| | 8 | b | 114 | 5| 6 5| 0 9| 5| | 9 | bbar | 114 | -5| 6 8| 0 5| 11| +----+--------+------+-----+------+------+----+ Note that if there are more than two outgoing partons, the first has status 113 and all the others 114. Each parton has JMOHEP(1,I)=6 to indicate the location of the hard c.m. for this subprocess, while JMOHEP(2,I) gives the location of the colour mother (treating the in- coming gluon as outgoing) or the connected electron. JDAHEP(1,I) will be set by the jet generator HWBGEN, while JDAHEP(2,I) points to the anticolour mother (or connected electron). Finally the HERWIG identi- fiers IDHW(I) could be set to the indicated values by means of the translation subroutine HWUIDT as follows: CHARACTER*8 NAME ..... NHEP=9 IDHEP(1)=11 IDHEP(2)=2212 ..... IDHEP(9)=-5 DO 10 I=1,NHEP 10 CALL HWUIDT(1,IDHEP(I),IDHW(I),NAME) IDHW(6)=15 The last statement is needed because IDPDG(I)=0 returns IDHW(I)=14. If subroutine HWBGEN is now called, it will find the coloured partons and generate QCD jets from them. Subsequent calls to HWCFOR etc can then be used to form clusters and hadronize them. If the hard subprocess routine is called from HWEPRO, like those already provided, it should have two options controlled by the logic- al variable GENEV in COMMON/HWHARD/. For GENEV=.FALSE., an event weight (normally the cross section in nanobarns) is generated and stored as EVWGT in COMMON/HWEVNT/. If this weight is accepted by HWEPRO, the subroutine is called a second time with GENEV=.TRUE. and the corresponding event data should then be generated and stored as explained above. ------------------------------------------------------------------------ ****** 20. ERROR CONDITIONS ****** Certain combinations of input parameters may lead to problems in exe- cution. HERWIG tries to detect these and print a warning. Errors during execution are dealt with by HWWARN which prints the calling subprogram and a code and takes appropriate action. In general, the larger the code the more serious the problem. Refer to the source code to find out why HWWARN was called. Events can be rerun by setting the random number seeds NRN to the values given in the error message or event dump, and MAXWGT to the maximum weight encountered in the run. Contents of /HEPEVT/ can by printed by calling HWUEPR, those of /HWPART/ (last parton shower) by HWUBPR. If WGTMAX is increased during event generation, so that this message is printed: HWWARN CALLED FROM SUBPROGRAM HWEPRO: CODE = 1 EVENT 21: SEEDS = 836291635 & 1823648329 WEIGHT = 0.3893E-08 EVENT SURVIVES. EXECUTION CONTINUES NEW MAXIMUM WEIGHT = 0.428217360829367E-08 then to regenerate any later events, WGTMAX must be set to the printed value, as well as setting NRN to the appropriate seeds. Examples of error messages: HWWARN CALLED FROM SUBPROGRAM HWSBRN: CODE = 101 EVENT 31: SEEDS = 422399901 & 771980111 WEIGHT = 0.3893E-08 EVENT KILLED. EXECUTION CONTINUES Spacelike (initial-state) parton branching had no phase space. This can happen due to cutoffs which are slightly different in the hard subprocess and the parton shower. Action taken: program throws away this event and starts a new one. HWWARN CALLED FROM SUBPROGRAM HWCHAD: CODE = 102 EVENT 51: SEEDS = 1033784787 & 1428957533 WEIGHT = 0.3893E-08 EVENT KILLED. EXECUTION CONTINUES A cluster has been formed with too low a mass to represent any hadron of the correct flavour, and there is no colour-connected cluster from which the necessary additional mass could be transferred. Action taken: program throws away this event and starts a new one. HWWARN CALLED FROM SUBPROGRAM HWUINE: CODE= 200 EVENT SURVIVES. RUN ENDS GRACEFULLY CPU time limit liable to be reached before generating MAXEV events. Action taken: skips to terminal calculations using existing events. HWWARN CALLED FROM SUBPROGRAM HWBSUD: CODE= 500 RUN CANNOT CONTINUE The table of Sudakov form factors read on unit LRSUD does not extend to the maximum momentum scale (QLIM) specified for this run. Action taken: run aborted. The user must either reduce QLIM or set LRSUD=0 to make a bigger table (set LWSUD nonzero to write it). HWWARN CALLED FROM SUBPROGRAM HWBSUD: CODE= 515 RUN CANNOT CONTINUE The table of Sudakov form factors read on unit LRSUD is for a diff- erent value of a relevant parameter (in this case the b quark mass). Action taken: run aborted. The user must make a new table (set LWSUD nonzero to write it). ------------------------------------------------------------------------ ****** 21. SAMPLE OUTPUT ****** Below we give a complete listing of output from version 5.9 of the program, set up for t quark production in pbar-p collisions at a c.m. energy of 1.8 TeV. To shorten the event record, the underlying event has been turned off (IPROC = 11706) and production vertices are not printed (PRVTX=.FALSE.). The main features of the output are discussed in section 22. HERWIG 5.9 22nd July 1996 Please reference: G. Marchesini, B.R. Webber, G.Abbiendi, I.G.Knowles, M.H.Seymour & L.Stanco Computer Physics Communications 67 (1992) 465 INPUT CONDITIONS FOR THIS RUN BEAM 1 (PBAR ) MOM. = 900.00 BEAM 2 (P ) MOM. = 900.00 PROCESS CODE (IPROC) = 11706 NUMBER OF FLAVOURS = 6 STRUCTURE FUNCTION SET = 5 AZIM SPIN CORRELATIONS = T AZIM SOFT CORRELATIONS = T QCD LAMBDA (GEV) = 0.1800 DOWN QUARK MASS = 0.3200 UP QUARK MASS = 0.3200 STRANGE QUARK MASS = 0.5000 CHARMED QUARK MASS = 1.5500 BOTTOM QUARK MASS = 4.9500 TOP QUARK MASS = 170.0000 GLUON EFFECTIVE MASS = 0.7500 EXTRA SHOWER CUTOFF (Q)= 0.4800 EXTRA SHOWER CUTOFF (G)= 0.1000 PHOTON SHOWER CUTOFF = 0.4000 CLUSTER MASS PARAMETER = 3.3500 SPACELIKE EVOLN CUTOFF = 2.5000 INTRINSIC P-TRAN (RMS) = 0.0000 MIN P-TRAN FOR 2->2 = 10.0000 MAX P-TRAN FOR 2->2 = 900.0002 NO EVENTS WILL BE WRITTEN TO DISK B_d: Delt-M/Gam =0.7000 Delt-Gam/2*Gam =0.0000 B_s: Delt-M/Gam = 10.00 Delt-Gam/2*Gam =0.2000 PDFLIB NOT USED FOR BEAM 1 PDFLIB NOT USED FOR BEAM 2 Checking consistency of particle properties Checking consistency of decay tables Line, 565 decay: LMBDA_C+ --> XI*0 K*+ is kinematically not allowed, Min-Mout= -0.139 LMBDA_C+: BR sum = 0.97800 Rescaling to 1 Line, 990 decay: LMBDA_C- --> XI*BAR K*- is kinematically not allowed, Min-Mout= -0.139 LMBDA_C-: BR sum = 0.97800 Rescaling to 1 PARTICLE TYPE 21=PI0 SET STABLE INITIAL SEARCH FOR MAX WEIGHT PROCESS CODE IPROC = 11706 RANDOM NO. SEED 1 = 1246579 SEED 2 = 8447766 NUMBER OF SHOTS = 2000 NEW MAXIMUM WEIGHT = 1.1503371195500599E-03 NEW MAXIMUM WEIGHT = 3.2720875047931022E-03 NEW MAXIMUM WEIGHT = 3.4397725453424351E-02 NEW MAXIMUM WEIGHT = 6.0381232770162795E-02 NEW MAXIMUM WEIGHT = 6.6570674949068473E-02 INITIAL SEARCH FINISHED OUTPUT ON ELEMENTARY PROCESS NUMBER OF EVENTS = 0 NUMBER OF WEIGHTS = 2000 MEAN VALUE OF WGT = 4.5373E-03 RMS SPREAD IN WGT = 9.3312E-03 ACTUAL MAX WEIGHT = 6.0519E-02 ASSUMED MAX WEIGHT = 6.6571E-02 PROCESS CODE IPROC = 11706 CROSS SECTION (PB) = 4.537 ERROR IN C-S (PB) = 0.2087 EFFICIENCY PERCENT = 6.816 EVENT 39: 900.00 GEV/C PBAR ON 900.00 GEV/C P PROCESS: 11706 SEEDS: 875163092 & 655954870 STATUS: 100 ERROR: 0 WEIGHT: 0.4537E-02 ---INITIAL STATE--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 1 PBAR -2212 101 0 0 0 0 0.00 0.00 900.00 900.00 0.94 2 P 2212 102 0 0 0 0 0.00 0.00 -900.00 900.00 0.94 3 CMF 0 103 1 2 0 0 0.00 0.00 0.00 1800.00 1800.00 ---HARD SUBPROCESS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 4 UBAR -2 121 6 7 9 5 0.00 0.00 312.09 312.09 0.32 5 UQRK 2 122 6 4 17 8 0.00 0.00 -169.95 169.95 0.32 6 HARD 0 120 4 5 7 8 -16.42 -3.93 142.14 482.34 460.61 7 TBAR -6 123 6 8 22 4 116.29 -61.69 157.43 266.49 170.00 8 TQRK 6 124 6 5 24 7 -116.29 61.69 -15.29 215.55 170.00 ---PARTON SHOWERS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 9 UBAR 94 141 4 6 11 16 -19.27 -6.00 314.16 310.83 -49.90 10 CONE 0 100 4 7 0 0 0.88 -0.47 0.53 1.13 0.00 11 UBARDBAR -2101 2 9 12 45 21 0.00 0.00 408.95 408.95 0.70 12 GLUON 21 2 9 13 46 47 8.42 0.19 140.64 140.89 0.75 13 GLUON 21 2 9 14 48 49 2.07 -1.20 14.47 14.68 0.75 14 DBAR -1 2 9 15 50 49 3.78 3.25 8.85 10.16 0.32 15 DQRK 1 2 9 16 51 50 3.65 2.24 9.47 10.40 0.32 16 GLUON 21 2 9 26 52 53 1.36 1.52 3.46 4.09 0.75 17 UQRK 94 142 5 6 19 21 2.85 2.07 -172.02 171.51 -13.73 18 CONE 0 100 5 8 0 0 -0.88 0.47 0.07 1.00 0.00 19 GLUON 21 2 17 20 54 55 -0.95 -0.97 -3.31 3.66 0.75 20 GLUON 21 2 17 21 56 57 -1.90 -1.10 -16.01 16.17 0.75 21 UD 2101 2 17 45 58 57 0.00 0.00 -708.66 708.66 1.04 22 TBAR 94 143 7 6 23 23 107.70 -63.75 156.89 263.01 170.00 23 TBAR -6 3 22 22 26 26 107.70 -63.75 156.89 263.01 170.00 24 TQRK 94 144 8 6 25 25 -124.12 59.82 -14.74 219.32 170.00 25 TQRK 6 3 24 24 37 37 -124.12 59.82 -14.74 219.32 170.00 ---HEAVY FLAVOUR DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 26 TBAR -6 155 22 37 27 29 107.70 -63.75 156.89 263.01 170.00 27 MU- 13 123 26 28 30 28 18.31 32.76 65.37 75.38 0.11 28 NU_MUBAR -14 124 26 27 31 27 80.30 -57.83 106.04 145.04 0.00 29 BBAR -5 124 26 26 32 26 9.09 -38.68 -14.52 42.60 4.95 30 MU- 13 1 27 26 0 0 17.82 31.88 63.62 73.36 0.11 31 NU_MUBAR -14 1 28 26 0 0 78.14 -56.28 103.19 141.14 0.00 ---PARTON SHOWERS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 32 BBAR 94 144 29 26 34 36 11.74 -39.36 -9.92 48.52 23.85 33 CONE 0 100 29 26 0 0 0.24 0.72 1.07 1.32 0.00 34 GLUON 21 2 32 35 59 60 -2.95 -0.95 -3.35 4.62 0.75 35 GLUON 21 2 32 36 61 62 -1.72 -1.41 -1.55 2.81 0.75 36 BBAR -5 2 32 44 63 62 16.41 -37.00 -5.02 41.08 4.95 ---HEAVY FLAVOUR DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 37 TQRK 6 155 24 19 38 40 -124.12 59.82 -14.74 219.32 170.00 38 NU_E 12 123 37 39 41 39 -96.15 66.72 23.37 119.34 0.00 39 E+ -11 124 37 38 42 38 6.38 13.33 -54.59 56.56 0.00 40 BQRK 5 124 37 37 43 37 -34.36 -20.23 16.48 43.43 4.95 41 NU_E 12 1 38 37 0 0 -96.15 66.72 23.37 119.34 0.00 42 E+ -11 1 39 37 0 0 6.38 13.33 -54.59 56.56 0.00 ---PARTON SHOWERS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 43 BQRK 94 144 40 37 44 44 -34.36 -20.23 16.48 43.43 4.95 44 BQRK 5 2 43 54 64 63 -34.36 -20.23 16.48 43.43 4.95 ---GLUON SPLITTING--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 45 UBARDBAR -2101 161 9 65 85 58 0.01 0.00 279.95 279.95 0.64 46 UBAR -2 158 9 47 104 84 1.90 0.01 33.44 33.50 0.32 47 UQRK 2 158 9 69 86 46 3.96 0.11 64.98 65.11 0.32 48 DBAR -1 158 9 49 97 70 0.95 -0.68 7.08 7.18 0.32 49 DQRK 1 158 9 71 87 48 0.40 -0.05 2.32 2.38 0.32 50 DBAR -1 158 9 51 98 72 3.00 2.57 7.04 8.08 0.32 51 DQRK 1 158 9 52 88 50 3.65 2.24 9.47 10.40 0.32 52 DBAR -1 158 9 53 88 51 0.49 0.47 0.95 1.21 0.32 53 DQRK 1 158 9 73 89 52 0.79 0.96 2.29 2.62 0.32 54 DBAR -1 158 17 55 102 80 -0.23 -0.13 -0.54 0.68 0.32 55 DQRK 1 158 17 56 90 54 -0.62 -0.80 -2.35 2.58 0.32 56 DBAR -1 158 17 57 90 55 -1.18 -0.54 -8.28 8.38 0.32 57 DQRK 1 158 17 75 91 56 -0.34 -0.26 -5.03 5.06 0.32 58 UD 2101 162 17 45 96 68 0.00 0.00 -552.77 552.77 0.64 59 DBAR -1 158 32 60 99 74 -0.85 -0.40 -0.95 1.37 0.32 60 DQRK 1 158 32 61 92 59 -1.65 -0.34 -1.90 2.56 0.32 61 DBAR -1 158 32 62 92 60 -0.66 -0.74 -0.83 1.33 0.32 62 DQRK 1 158 32 77 93 61 -0.91 -0.59 -0.62 1.29 0.32 63 BBAR -5 158 32 64 101 78 14.03 -31.87 -4.37 35.44 4.95 64 BQRK 5 158 43 81 94 63 -24.17 -14.23 11.39 30.68 4.95 65 DBAR -1 159 9 66 85 45 0.06 0.00 30.61 30.61 0.32 66 DQRK 1 159 9 83 95 65 0.02 0.00 65.93 65.93 0.32 67 UBAR -2 159 17 68 100 76 0.00 0.00 -108.31 108.31 0.32 68 UQRK 2 159 17 58 96 67 -0.02 -0.02 -26.64 26.65 0.32 69 DBAR -1 159 9 70 86 47 0.44 -0.20 4.71 4.75 0.32 70 DQRK 1 159 9 48 97 69 2.01 0.04 32.91 32.97 0.32 71 SBAR -3 159 9 72 87 49 0.67 0.43 2.09 2.29 0.50 72 SQRK 3 159 9 50 98 71 0.55 0.00 2.95 3.04 0.50 73 UBAR -2 159 32 74 89 53 -0.35 -0.15 -0.36 0.61 0.32 74 UQRK 2 159 9 59 99 73 -0.02 0.04 0.09 0.33 0.32 75 SBAR -3 159 17 76 91 57 -0.10 -0.08 -15.37 15.37 0.50 76 SQRK 3 159 17 67 100 75 -0.26 -0.20 -8.28 8.30 0.50 77 SBAR -3 159 32 78 93 62 1.73 -3.90 -0.53 4.33 0.50 78 SQRK 3 159 32 63 101 77 0.49 -1.31 -0.22 1.50 0.50 79 DBAR -1 159 17 80 103 82 -0.22 -0.12 -0.18 0.45 0.32 80 DQRK 1 159 43 54 102 79 -3.20 -1.89 1.55 4.04 0.32 81 UBAR -2 159 17 82 94 64 -1.26 -0.74 0.58 1.61 0.32 82 UQRK 2 159 43 79 103 81 -5.60 -3.30 2.72 7.05 0.32 83 DBAR -1 159 9 84 95 66 0.07 0.00 27.33 27.33 0.32 84 DQRK 1 159 9 46 104 83 0.23 0.00 11.57 11.58 0.32 ---CLUSTER FORMATION--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 85 CLUS 91 184 45 65 105 106 0.07 0.00 310.56 310.56 1.23 86 CLUS 91 183 47 69 107 108 4.40 -0.09 69.69 69.85 1.59 87 CLUS 91 183 49 71 109 110 1.07 0.38 4.41 4.67 1.03 88 CLUS 91 183 51 52 111 112 4.14 2.70 10.42 11.61 1.31 89 CLUS 91 183 53 73 113 114 0.44 0.80 1.92 3.24 2.44 90 CLUS 91 183 55 56 115 116 -1.80 -1.34 -10.63 10.96 1.48 91 CLUS 91 183 57 75 117 118 -0.44 -0.34 -20.39 20.43 1.09 92 CLUS 91 183 60 61 119 120 -2.31 -1.08 -2.73 3.89 1.09 93 CLUS 91 183 62 77 121 122 0.82 -4.49 -1.15 5.62 3.07 94 CLUS 91 183 64 81 123 123 -25.44 -14.98 11.97 32.29 5.28 95 CLUS 91 183 66 83 124 125 0.09 0.00 93.26 93.26 0.71 96 CLUS 91 185 68 58 126 127 -0.02 -0.02 -579.41 579.41 1.64 97 CLUS 91 183 70 48 128 129 2.97 -0.64 39.98 40.15 2.04 98 CLUS 91 183 72 50 130 131 3.54 2.57 9.99 11.12 2.17 99 CLUS 91 183 74 59 132 133 -0.87 -0.36 -0.86 1.71 1.13 100 CLUS 91 183 76 67 134 135 -0.26 -0.20 -116.59 116.61 2.24 101 CLUS 91 183 78 63 136 136 14.56 -33.17 -4.60 36.91 5.38 102 CLUS 91 183 80 54 137 138 -3.47 -2.02 1.02 4.76 2.34 103 CLUS 91 183 82 79 139 140 -5.81 -3.42 2.54 7.49 2.06 104 CLUS 91 183 84 46 141 142 2.13 0.01 45.01 45.08 1.04 ---CLUSTER DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 105 PBAR -2212 1 85 9 0 0 -0.13 0.09 215.09 215.09 0.94 106 PI+ 211 1 85 9 0 0 0.20 -0.09 95.47 95.47 0.14 107 OMEGA 223 197 86 9 143 145 2.33 -0.03 34.12 34.20 0.78 108 RHO+ 213 197 86 9 146 147 2.07 -0.06 35.58 35.65 0.77 109 PI0 111 1 87 9 0 0 0.14 0.05 0.57 0.60 0.14 110 K*0 313 197 87 9 148 149 0.93 0.34 3.84 4.07 0.90 111 PI0 111 1 88 9 0 0 2.48 1.51 6.44 7.07 0.14 112 OMEGA 223 197 88 9 150 151 1.66 1.19 3.98 4.54 0.78 113 P 2212 1 89 9 0 0 -0.35 0.36 0.89 1.39 0.94 114 DLTABR-- -2224 197 89 9 152 153 0.80 0.45 1.03 1.85 1.23 115 A_10 20113 197 90 17 154 155 -1.73 -1.30 -10.33 10.63 1.23 116 PI0 111 1 90 17 0 0 -0.06 -0.04 -0.30 0.33 0.14 117 PI- -211 1 91 17 0 0 -0.08 0.11 -12.23 12.23 0.14 118 K+ 321 1 91 17 0 0 -0.36 -0.44 -8.16 8.20 0.49 119 RHO- -213 197 92 32 156 157 -1.94 -1.07 -2.51 3.44 0.77 120 PI+ 211 1 92 32 0 0 -0.37 0.00 -0.22 0.45 0.14 121 KL_10 10313 197 93 32 158 159 1.17 -2.31 -1.07 3.22 1.57 122 ETAP 331 197 93 32 160 162 -0.35 -2.18 -0.08 2.41 0.96 123 B- -521 196 94 43 163 165 -25.44 -14.98 11.97 32.29 5.28 124 PI0 111 1 95 9 0 0 0.30 -0.06 25.24 25.24 0.14 125 PI0 111 1 95 9 0 0 -0.21 0.06 68.02 68.02 0.14 126 PI+ 211 1 96 17 0 0 0.04 0.14 -231.52 231.52 0.14 127 DELTA0 2114 197 96 17 166 167 -0.06 -0.15 -347.89 347.89 1.23 128 P 2212 1 97 9 0 0 0.84 -0.11 14.92 14.97 0.94 129 PBAR -2212 1 97 9 0 0 2.13 -0.53 25.06 25.17 0.94 130 ETA 221 197 98 9 168 170 0.59 0.27 2.25 2.40 0.55 131 K*_2BAR0 -315 197 98 9 171 172 2.95 2.30 7.74 8.72 1.43 132 PI0 111 1 99 9 0 0 -0.35 0.05 -0.95 1.02 0.14 133 PI+ 211 1 99 9 0 0 -0.52 -0.41 0.09 0.68 0.14 134 KBAR0 -311 197 100 17 173 173 0.04 -0.01 -17.14 17.15 0.50 135 PI_2- -10215 197 100 17 174 175 -0.30 -0.19 -99.44 99.46 1.67 136 B_S0 531 200 101 32 176 176 14.56 -33.17 -4.60 36.91 5.38 137 HL_10 10223 197 102 43 177 178 -3.20 -1.92 1.24 4.10 1.17 138 ETA 221 197 102 43 179 181 -0.28 -0.10 -0.22 0.66 0.55 139 A_20 115 197 103 43 182 184 -2.96 -1.35 1.04 3.66 1.32 140 PI+ 211 1 103 43 0 0 -2.85 -2.07 1.50 3.84 0.14 141 PI0 111 1 104 9 0 0 0.66 0.06 16.64 16.65 0.14 142 RHO- -213 197 104 9 185 186 1.47 -0.05 28.37 28.42 0.77 ---STRONG HADRON DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 143 PI+ 211 1 107 9 0 0 1.90 -0.02 24.27 24.35 0.14 144 PI- -211 1 107 9 0 0 0.32 0.00 6.77 6.78 0.14 145 PI0 111 1 107 9 0 0 0.11 -0.02 3.07 3.08 0.14 146 PI+ 211 1 108 9 0 0 1.80 0.19 29.01 29.07 0.14 147 PI0 111 1 108 9 0 0 0.27 -0.25 6.57 6.58 0.14 148 K0 311 198 110 9 187 187 0.65 0.06 3.19 3.29 0.50 149 PI0 111 1 110 9 0 0 0.28 0.27 0.65 0.77 0.14 150 PI0 111 1 112 9 0 0 1.33 1.12 3.73 4.12 0.14 151 GAMMA 22 1 112 9 0 0 0.34 0.07 0.25 0.42 0.00 152 PBAR -2212 1 114 9 0 0 0.75 0.24 1.02 1.59 0.94 153 PI- -211 1 114 9 0 0 0.05 0.21 0.01 0.25 0.14 154 RHO+ 213 198 115 17 188 189 -1.57 -0.83 -8.84 9.05 0.77 155 PI- -211 1 115 17 0 0 -0.16 -0.47 -1.49 1.58 0.14 156 PI- -211 1 119 32 0 0 -0.65 -0.64 -1.38 1.66 0.14 157 PI0 111 1 119 32 0 0 -1.29 -0.43 -1.12 1.77 0.14 158 K+ 321 1 121 32 0 0 0.56 -0.88 0.04 1.15 0.49 159 RHO- -213 198 121 32 190 191 0.61 -1.43 -1.11 2.06 0.77 160 PI+ 211 1 122 32 0 0 -0.15 -0.86 0.05 0.89 0.14 161 PI- -211 1 122 32 0 0 -0.07 -0.48 -0.08 0.51 0.14 162 ETA 221 198 122 32 192 193 -0.13 -0.84 -0.05 1.01 0.55 163 RHO0 113 198 123 43 194 195 -18.44 -9.34 6.79 21.77 0.77 164 E- 11 1 123 43 0 0 -6.49 -5.26 5.27 9.88 0.00 165 NU_EBAR -12 1 123 43 0 0 -0.50 -0.38 -0.09 0.63 0.00 166 P 2212 1 127 17 0 0 0.09 -0.11 -219.33 219.33 0.94 167 PI- -211 1 127 17 0 0 -0.15 -0.05 -128.56 128.56 0.14 168 PI0 111 1 130 9 0 0 0.07 0.07 0.80 0.82 0.14 169 PI0 111 1 130 9 0 0 0.21 0.13 0.47 0.55 0.14 170 PI0 111 1 130 9 0 0 0.31 0.07 0.98 1.04 0.14 171 K- -321 1 131 9 0 0 2.36 1.08 5.22 5.85 0.49 172 PI+ 211 1 131 9 0 0 0.59 1.22 2.53 2.87 0.14 173 K_S0 310 198 134 17 196 197 0.04 -0.01 -17.14 17.15 0.50 174 F_2 225 198 135 17 198 199 -0.33 -0.32 -95.89 95.90 1.27 175 PI- -211 1 135 17 0 0 0.03 0.12 -3.56 3.56 0.14 176 B_SBAR0 -531 199 136 32 207 208 14.56 -33.17 -4.60 36.91 5.38 177 RHO+ 213 198 137 43 200 201 -2.29 -1.73 0.99 3.13 0.77 178 PI- -211 1 137 43 0 0 -0.90 -0.19 0.24 0.96 0.14 179 PI0 111 1 138 43 0 0 0.01 0.05 0.02 0.15 0.14 180 PI0 111 1 138 43 0 0 -0.07 -0.10 -0.06 0.19 0.14 181 PI0 111 1 138 43 0 0 -0.22 -0.05 -0.18 0.32 0.14 182 OMEGA 223 198 139 43 202 204 -1.92 -0.63 0.73 2.28 0.78 183 PI+ 211 1 139 43 0 0 -0.66 -0.32 0.05 0.75 0.14 184 PI- -211 1 139 43 0 0 -0.38 -0.40 0.26 0.63 0.14 185 PI- -211 1 142 9 0 0 0.68 -0.38 13.27 13.29 0.14 186 PI0 111 1 142 9 0 0 0.79 0.33 15.11 15.13 0.14 187 K_S0 310 198 148 9 205 206 0.65 0.06 3.19 3.29 0.50 188 PI+ 211 1 154 17 0 0 -1.45 -0.73 -8.47 8.62 0.14 189 PI0 111 1 154 17 0 0 -0.13 -0.10 -0.37 0.43 0.14 190 PI- -211 1 159 32 0 0 0.68 -1.24 -1.13 1.82 0.14 191 PI0 111 1 159 32 0 0 -0.06 -0.19 0.02 0.24 0.14 192 GAMMA 22 1 162 32 0 0 -0.31 -0.62 -0.15 0.71 0.00 193 GAMMA 22 1 162 32 0 0 0.18 -0.22 0.10 0.30 0.00 194 PI+ 211 1 163 43 0 0 -16.47 -8.12 6.03 19.32 0.14 195 PI- -211 1 163 43 0 0 -1.98 -1.22 0.76 2.45 0.14 196 PI0 111 1 173 17 0 0 0.14 0.16 -6.36 6.37 0.14 197 PI0 111 1 173 17 0 0 -0.10 -0.16 -10.78 10.78 0.14 198 PI0 111 1 174 17 0 0 -0.61 -0.52 -38.85 38.86 0.14 199 PI0 111 1 174 17 0 0 0.27 0.20 -57.03 57.04 0.14 200 PI+ 211 1 177 43 0 0 -1.01 -0.34 0.30 1.11 0.14 201 PI0 111 1 177 43 0 0 -1.29 -1.39 0.70 2.02 0.14 202 PI+ 211 1 182 43 0 0 -0.30 -0.02 0.08 0.34 0.14 203 PI- -211 1 182 43 0 0 -0.30 -0.13 0.36 0.50 0.14 204 PI0 111 1 182 43 0 0 -1.32 -0.48 0.29 1.44 0.14 205 PI0 111 1 187 9 0 0 0.51 -0.06 1.56 1.65 0.14 206 PI0 111 1 187 9 0 0 0.14 0.12 1.63 1.64 0.14 ---HEAVY FLAVOUR DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 207 BQRK 5 155 176 208 209 211 13.20 -30.08 -4.17 33.47 4.88 208 SBAR -3 125 176 211 212 211 1.35 -3.09 -0.43 3.43 0.50 209 CQRK 4 123 207 210 213 210 2.30 -5.94 -0.61 6.59 1.55 210 CBAR -4 124 207 209 215 209 3.58 -8.37 -1.74 9.40 1.55 211 SQRK 3 124 207 207 217 207 7.33 -15.77 -1.82 17.49 0.50 212 SBAR -3 160 208 221 223 221 1.35 -3.09 -0.43 3.43 0.50 ---PARTON SHOWERS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 213 CQRK 94 143 209 207 214 214 2.30 -5.94 -0.61 6.59 1.55 214 CQRK 4 2 213 216 219 216 2.30 -5.94 -0.61 6.59 1.55 215 CBAR 94 144 210 207 216 216 3.58 -8.37 -1.74 9.40 1.55 216 CBAR -4 2 215 219 220 219 3.58 -8.37 -1.74 9.40 1.55 217 SQRK 94 144 211 207 218 218 7.33 -15.77 -1.82 17.49 0.50 218 SQRK 3 2 217 212 221 212 7.33 -15.77 -1.82 17.49 0.50 ---GLUON SPLITTING--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 219 CQRK 4 158 213 220 222 220 2.30 -5.94 -0.61 6.59 1.55 220 CBAR -4 158 215 219 222 219 3.58 -8.37 -1.74 9.40 1.55 221 SQRK 3 158 217 212 223 212 7.33 -15.77 -1.82 17.49 0.50 ---CLUSTER FORMATION--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 222 CLUS 91 183 219 220 224 224 4.87 -12.18 -2.12 13.62 2.98 223 CLUS 91 183 221 212 225 226 9.69 -20.99 -2.48 23.29 1.37 ---CLUSTER DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 224 ETA_C 441 199 222 213 227 229 4.87 -12.18 -2.12 13.62 2.98 225 K- -321 1 223 217 0 0 8.22 -17.67 -2.03 19.60 0.49 226 K+ 321 1 223 217 0 0 1.47 -3.31 -0.45 3.69 0.49 ---HEAVY FLAVOUR DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 227 GLUON 21 123 224 229 230 228 2.59 -4.45 -1.11 5.32 0.75 228 GLUON 21 124 224 227 232 229 0.84 -4.20 -0.51 4.38 0.75 229 GLUON 21 124 224 228 234 227 1.44 -3.53 -0.50 3.92 0.75 ---PARTON SHOWERS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 230 GLUON 94 143 227 224 231 231 2.59 -4.45 -1.11 5.32 0.75 231 GLUON 21 2 230 235 236 237 2.59 -4.45 -1.11 5.32 0.75 232 GLUON 94 144 228 224 233 233 0.84 -4.20 -0.51 4.38 0.75 233 GLUON 21 2 232 236 238 239 0.84 -4.20 -0.51 4.38 0.75 234 GLUON 94 144 229 224 235 235 1.44 -3.53 -0.50 3.92 0.75 235 GLUON 21 2 234 238 240 241 1.44 -3.53 -0.50 3.92 0.75 ---GLUON SPLITTING--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 236 DBAR -1 158 230 237 243 239 1.65 -2.62 -0.82 3.22 0.32 237 DQRK 1 158 230 240 242 236 0.95 -1.83 -0.29 2.10 0.32 238 DBAR -1 158 232 239 244 241 0.66 -3.17 -0.34 3.27 0.32 239 DQRK 1 158 232 236 243 238 0.18 -1.03 -0.17 1.11 0.32 240 UBAR -2 158 234 241 242 237 0.65 -2.08 -0.24 2.22 0.32 241 UQRK 2 158 234 238 244 240 0.79 -1.45 -0.26 1.70 0.32 ---CLUSTER FORMATION--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 242 CLUS 91 183 237 240 245 246 1.60 -3.90 -0.53 4.32 0.74 243 CLUS 91 183 239 236 247 248 1.82 -3.65 -0.98 4.33 1.03 244 CLUS 91 183 241 238 249 250 1.45 -4.62 -0.60 4.98 0.96 ---CLUSTER DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 245 PI- -211 1 242 230 0 0 1.53 -3.79 -0.46 4.11 0.14 246 PI0 111 1 242 230 0 0 0.06 -0.12 -0.07 0.20 0.14 247 PI0 111 1 243 232 0 0 0.52 -0.39 0.03 0.66 0.14 248 PI0 111 1 243 232 0 0 1.30 -3.27 -1.01 3.66 0.14 249 PI0 111 1 244 234 0 0 1.02 -3.98 -0.74 4.18 0.14 250 PI+ 211 1 244 234 0 0 0.43 -0.64 0.14 0.80 0.14 OUTPUT ON ELEMENTARY PROCESS NUMBER OF EVENTS = 1000 NUMBER OF WEIGHTS = 14518 MEAN VALUE OF WGT = 4.4894E-03 RMS SPREAD IN WGT = 9.2221E-03 ACTUAL MAX WEIGHT = 6.1048E-02 ASSUMED MAX WEIGHT = 6.6571E-02 PROCESS CODE IPROC = 11706 CROSS SECTION (PB) = 4.489 ERROR IN C-S (PB) = 7.6538E-02 EFFICIENCY PERCENT = 6.744 ----------------------------------------------------------------------- ****** 22. GUIDE TO SAMPLE OUTPUT ****** After listing the more important input parameter values, the program prints the message NO EVENTS WILL BE WRITTEN TO DISK to remind the user that LWEVT=0 for this run. Since BBbar oscillation is enabled (MIXING=.TRUE.), the relevant parameters are printed: B_d: Delt-M/Gam =0.7000 Delt-Gam/2*Gam =0.0000 B_s: Delt-M/Gam = 10.00 Delt-Gam/2*Gam =0.2000 The messages PDFLIB NOT USED FOR BEAM 1 PDFLIB NOT USED FOR BEAM 2 indicating that the CERN PDFLIB structure function library will not be used (MODPDF<0). Next the particle property and decay tables are checked for consistency. The messages Line, 565 decay: LMBDA_C+ --> XI*0 K*+ is kinematically not allowed, Min-Mout= -0.139 LMBDA_C+: BR sum = 0.97800 Rescaling to 1 Line, 990 decay: LMBDA_C- --> XI*BAR K*- is kinematically not allowed, Min-Mout= -0.139 LMBDA_C-: BR sum = 0.97800 Rescaling to 1 indicate that some user-modified decay modes are impossible and will be ignored. The default particle data table was modified by calling HWUSTA('PI0 ') to suppress pi0 decays, so we get the message PARTICLE TYPE 21=PI0 SET STABLE Next the program searches for the maximum weight, i.e. the maximum cross section in the available phase space, as implied by the default value WGTMAX=0. The parameters MIN P-TRAN FOR 2->2 = 10.0000 MAX P-TRAN FOR 2->2 = 900.0002 with PROCESS CODE = 11706 mean that the transverse momentum of the t quark in the QCD 2->2 hard subprocesses is required to be greater than 10 GeV/c. After this search, the estimated total cross section of relevant subprocesses in this region of phase space is printed, together with the anticipated efficiency of subprocess generation (i.e. average/maximum weight): CROSS SECTION (PB) = 4.537 ERROR IN C-S (PB) = 0.2087 EFFICIENCY PERCENT = 6.816 Since the print parameter was MAXPR=0, no events were printed by default, but the user analysis routine HWANAL called HWUEPR to print the first "interesting" event. The event heading EVENT 39: 900.00 GEV/C PBAR ON 900.00 GEV/C P PROCESS: 11706 SEEDS: 875163092 & 655954870 STATUS: 100 ERROR: 0 WEIGHT: 0.4537E-02 tells us the beam and target, the random number seeds at the start of the event and the process code IPROC. The status 100 means a complete event was generated and the zero error code means no problems were encountered. Since NOWGT=.TRUE. (unweighted event generation), each event has the mean weight computed earlier. Next come the contents of COMMON/HEPEVT/ and related quantities. The print parameter for vertex information has been set PRVTX=.FALSE. and so no space-time information is printed. The various parts of this particular event are located as follows: +---------+--------------------------------------+ | Entry | Description | +---------+--------------------------------------+ | 1- 3 | Initial state | | 4- 8 | Hard subprocess: u+ubar -> t+tbar | | 9- 25 | Parton showers | | 26- 44 | Top decays and subsequent showers | | 45- 84 | Gluon splitting | | 85-104 | Cluster formation | | 105-206 | Cluster and hadron decays | | 207-218 | Weak decay of B_sbar and showers | | 219-226 | Hadronization of B_sbar products | | 227-235 | 3-gluon decay of eta_c | | 236-250 | Hadronization of eta_c products | +---------+--------------------------------------+ We discuss each part in turn. ---INITIAL STATE--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 1 PBAR -2212 101 0 0 0 0 0.00 0.00 900.00 900.00 0.94 2 P 2212 102 0 0 0 0 0.00 0.00 -900.00 900.00 0.94 3 CMF 0 103 1 2 0 0 0.00 0.00 0.00 1800.00 1800.00 CMF represents the overall centre of mass of the initial state. The 'mother' MOi=JMOHEP(i,IHEP) & 'daughter' DAi=JDAHEP(i,IHEP) pointers are set to zero for these entries. ---HARD SUBPROCESS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 4 UBAR -2 121 6 7 9 5 0.00 0.00 312.09 312.09 0.32 5 UQRK 2 122 6 4 17 8 0.00 0.00 -169.95 169.95 0.32 6 HARD 0 120 4 5 7 8 -16.42 -3.93 142.14 482.34 460.61 7 TBAR -6 123 6 8 22 4 116.29 -61.69 157.43 266.49 170.00 8 TQRK 6 124 6 5 24 7 -116.29 61.69 -15.29 215.55 170.00 HARD is the hard subprocess centre of mass. Its mother and daughter pointers give the locations of the incoming and outgoing partons. The status codes 121-124 correspond to the hard subprocess partons 1-4. The first mother pointers show the location of the hard c.m., and the second mother of each parton is the 'colour mother', as explained above. Thus the colours of partons 1234 are connected to 3142 respt., corresponding to process IHPRO=12. Likewise,the first daughter points to the associated jet but the second daughter is the colour daughter, i.e. the parton to which this one's anticolour is connected. Thus the anticolour connections of 1234 in this case are to 2413. The colour diagram is (ubar)1 --<--+ +--<-- 3(tbar) \___/ ___ / \ (u)2 -->--+ +-->-- 4(t) Note that in specifying the colour connections all lines are regarded as outgoing, and that since antiquarks carry no colour MO2 is in that case used for the flavour connection (similarly with DA2 for quarks). Gluon radiation from the initial ubar will be limited by interference with the tbar and vice-versa, that from the incoming u by the t and vice-versa. At this stage, the momenta and masses of the partons are the raw on-shell values generated before QCD radiative corrections, but HARD has been updated to give the true hard subprocess momentum after initial- and final-state parton branching. ---PARTON SHOWERS--- The QCD cascade from each hard parton is generated in sequence. First there is a jet entry (IDHEP=94) giving the total jet momentum, mass and flavour. For initial-state jets the mass represents -|q**2|**1/2 for the virtual parton entering the hard subprocess. MO1 gives the parent hard parton and MO2 the hard centre-of-mass. DO1 and DO2 point to the first and last parton in the jet after perturbative branching. If branching occurs, the next entry (CONE) is a lightlike 4-vector defining the radiation cone and the orientation of the radiation pattern. The partons in the jet (with ISTHEP set to 2 by gluon splitting sub- routine HWCGSP) have their colour and anticolour connections given by MO2 and DA2 respectively, as described for the hard subprocess. For an incoming jet, the remnants of the incoming hadrons (IHEP=11,21 here) also have ISTHEP=2. The ubar jet is: IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 9 UBAR 94 141 4 6 11 16 -19.27 -6.00 314.16 310.83 -49.90 10 CONE 0 100 4 7 0 0 0.88 -0.47 0.53 1.13 0.00 11 UBARDBAR -2101 2 9 12 45 21 0.00 0.00 408.95 408.95 0.70 12 GLUON 21 2 9 13 46 47 8.42 0.19 140.64 140.89 0.75 13 GLUON 21 2 9 14 48 49 2.07 -1.20 14.47 14.68 0.75 14 DBAR -1 2 9 15 50 49 3.78 3.25 8.85 10.16 0.32 15 DQRK 1 2 9 16 51 50 3.65 2.24 9.47 10.40 0.32 16 GLUON 21 2 9 26 52 53 1.36 1.52 3.46 4.09 0.75 and similarly for the u jet (IHEP=17-21). The produced t and tbar are so slow in the subprocess c.o.m. frame that they do not radiate any resolvable gluons. After any showering, they're given status ISTHEP=3 and copied with ISTHEP=155 retaining the colour connection labels for the decay processes. In this event both top decays are leptonic: ---HEAVY FLAVOUR DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 26 TBAR -6 155 22 37 27 29 107.70 -63.75 156.89 263.01 170.00 27 MU- 13 123 26 28 30 28 18.31 32.76 65.37 75.38 0.11 28 NU_MUBAR -14 124 26 27 31 27 80.30 -57.83 106.04 145.04 0.00 29 BBAR -5 124 26 26 32 26 9.09 -38.68 -14.52 42.60 4.95 30 MU- 13 1 27 26 0 0 17.82 31.88 63.62 73.36 0.11 31 NU_MUBAR -14 1 28 26 0 0 78.14 -56.28 103.19 141.14 0.00 37 TQRK 6 155 24 19 38 40 -124.12 59.82 -14.74 219.32 170.00 38 NU_E 12 123 37 39 41 39 -96.15 66.72 23.37 119.34 0.00 39 E+ -11 124 37 38 42 38 6.38 13.33 -54.59 56.56 0.00 40 BQRK 5 124 37 37 43 37 -34.36 -20.23 16.48 43.43 4.95 41 NU_E 12 1 38 37 0 0 -96.15 66.72 23.37 119.34 0.00 42 E+ -11 1 39 37 0 0 6.38 13.33 -54.59 56.56 0.00 ---PARTON SHOWERS--- After the tbar decay, the resulting bbar radiates 2 gluons: IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 32 BBAR 94 144 29 26 34 36 11.74 -39.36 -9.92 48.52 23.85 33 CONE 0 100 29 26 0 0 0.24 0.72 1.07 1.32 0.00 34 GLUON 21 2 32 35 59 60 -2.95 -0.95 -3.35 4.62 0.75 35 GLUON 21 2 32 36 61 62 -1.72 -1.41 -1.55 2.81 0.75 36 BBAR -5 2 32 44 63 62 16.41 -37.00 -5.02 41.08 4.95 but the b quark from the t decay does not radiate. If the decays had been hadronic, the quarks from the virtual W decay would also radiate in general. ---GLUON SPLITTING--- As the first step in the cluster hadronization model, any gluons in the jets are split into light quark-antiquark pairs. The flavours of the pairs are chosen at random amongst those allowed by kinematics. The colour connections are remade accordingly. IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 45 UBARDBAR -2101 161 9 65 85 58 0.01 0.00 279.95 279.95 0.64 46 UBAR -2 158 9 47 104 84 1.90 0.01 33.44 33.50 0.32 47 UQRK 2 158 9 69 86 46 3.96 0.11 64.98 65.11 0.32 48 DBAR -1 158 9 49 97 70 0.95 -0.68 7.08 7.18 0.32 49 DQRK 1 158 9 71 87 48 0.40 -0.05 2.32 2.38 0.32 ....... 63 BBAR -5 158 32 64 101 78 14.03 -31.87 -4.37 35.44 4.95 64 BQRK 5 158 43 81 94 63 -24.17 -14.23 11.39 30.68 4.95 Each quark (or antidiquark) is combined with its colour mother anti- quark (or diquark) to make a cluster with the sum of their 4-momenta. All non-beam clusters with masses above the maximum are split by creating new quark-antiquark pairs with ISTHEP=159 (10 such pairs in this event). 65 DBAR -1 159 9 66 85 45 0.06 0.00 30.61 30.61 0.32 66 DQRK 1 159 9 83 95 65 0.02 0.00 65.93 65.93 0.32 ....... 83 DBAR -1 159 9 84 95 66 0.07 0.00 27.33 27.33 0.32 84 DQRK 1 159 9 46 104 83 0.23 0.00 11.57 11.58 0.32 ---CLUSTER FORMATION--- Next the clusters themselves are listed. The mothers of a cluster are the partons from which it is made, and the daughters are the primary hadrons into which it decays. IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 85 CLUS 91 184 45 65 105 106 0.07 0.00 310.56 310.56 1.23 86 CLUS 91 183 47 69 107 108 4.40 -0.09 69.69 69.85 1.59 ....... 103 CLUS 91 183 82 79 139 140 -5.81 -3.42 2.54 7.49 2.06 104 CLUS 91 183 84 46 141 142 2.13 0.01 45.01 45.08 1.04 ---CLUSTER DECAYS--- The clusters, including the b-flavoured clusters 94 and 101, now decay, usually into pairs of hadrons chosen according to the density of states. Sometimes single-hadron decays occur, with transfer of momentum to a neighbouring cluster, if there is insufficient phase space for two-body decay. Note that cluster 94 actually did a 1-body decay into a B- (IHEP=123, ISTHEP=196). Hadrons with ISTHEP=1 are stable. ISTHEP=200 indicates a neutral B meson which may undergo flavour oscillation. IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 105 PBAR -2212 1 85 9 0 0 -0.13 0.09 215.09 215.09 0.94 106 PI+ 211 1 85 9 0 0 0.20 -0.09 95.47 95.47 0.14 107 OMEGA 223 197 86 9 143 145 2.33 -0.03 34.12 34.20 0.78 108 RHO+ 213 197 86 9 146 147 2.07 -0.06 35.58 35.65 0.77 ....... 123 B- -521 196 94 43 163 165 -25.44 -14.98 11.97 32.29 5.28 ....... 136 B_S0 531 200 101 32 176 176 14.56 -33.17 -4.60 36.91 5.38 ....... 141 PI0 111 1 104 9 0 0 0.66 0.06 16.64 16.65 0.14 142 RHO- -213 197 104 9 185 186 1.47 -0.05 28.37 28.42 0.77 ---STRONG HADRON DECAYS--- The unstable hadrons decay according to decay tables. Remember that the pi0 was set stable in the initialization phase. For heavy (b,c) quarks, partonic or direct hadronic decays may occur. In this event the B- does a b -> u directly to rho0 e- nu_ebar. The B_s oscillates into a B_sbar which decays partonically to c cbar s sbar. IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 143 PI+ 211 1 107 9 0 0 1.90 -0.02 24.27 24.35 0.14 144 PI- -211 1 107 9 0 0 0.32 0.00 6.77 6.78 0.14 145 PI0 111 1 107 9 0 0 0.11 -0.02 3.07 3.08 0.14 146 PI+ 211 1 108 9 0 0 1.80 0.19 29.01 29.07 0.14 147 PI0 111 1 108 9 0 0 0.27 -0.25 6.57 6.58 0.14 ....... 163 RHO0 113 198 123 43 194 195 -18.44 -9.34 6.79 21.77 0.77 164 E- 11 1 123 43 0 0 -6.49 -5.26 5.27 9.88 0.00 165 NU_EBAR -12 1 123 43 0 0 -0.50 -0.38 -0.09 0.63 0.00 ....... 176 B_SBAR0 -531 199 136 32 207 208 14.56 -33.17 -4.60 36.91 5.38 205 PI0 111 1 187 9 0 0 0.51 -0.06 1.56 1.65 0.14 206 PI0 111 1 187 9 0 0 0.14 0.12 1.63 1.64 0.14 ---HEAVY FLAVOUR DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 207 BQRK 5 155 176 208 209 211 13.20 -30.08 -4.17 33.47 4.88 208 SBAR -3 125 176 211 212 211 1.35 -3.09 -0.43 3.43 0.50 209 CQRK 4 123 207 210 213 210 2.30 -5.94 -0.61 6.59 1.55 210 CBAR -4 124 207 209 215 209 3.58 -8.37 -1.74 9.40 1.55 211 SQRK 3 124 207 207 217 207 7.33 -15.77 -1.82 17.49 0.50 212 SBAR -3 160 208 221 223 221 1.35 -3.09 -0.43 3.43 0.50 The B_sbar decay products hadronize to eta_c K+ K-: ---CLUSTER DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 224 ETA_C 441 199 222 213 227 229 4.87 -12.18 -2.12 13.62 2.98 225 K- -321 1 223 217 0 0 8.22 -17.67 -2.03 19.60 0.49 226 K+ 321 1 223 217 0 0 1.47 -3.31 -0.45 3.69 0.49 The eta_c decays partonically to 3 gluons: ---HEAVY FLAVOUR DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 227 GLUON 21 123 224 229 230 228 2.59 -4.45 -1.11 5.32 0.75 228 GLUON 21 124 224 227 232 229 0.84 -4.20 -0.51 4.38 0.75 229 GLUON 21 124 224 228 234 227 1.44 -3.53 -0.50 3.92 0.75 Finally the 3 gluons hadronize to pi+ pi- 4 pi0: ---CLUSTER DECAYS--- IHEP ID IDPDG IST MO1 MO2 DA1 DA2 P-X P-Y P-Z ENERGY MASS 245 PI- -211 1 242 230 0 0 1.53 -3.79 -0.46 4.11 0.14 246 PI0 111 1 242 230 0 0 0.06 -0.12 -0.07 0.20 0.14 247 PI0 111 1 243 232 0 0 0.52 -0.39 0.03 0.66 0.14 248 PI0 111 1 243 232 0 0 1.30 -3.27 -1.01 3.66 0.14 249 PI0 111 1 244 234 0 0 1.02 -3.98 -0.74 4.18 0.14 250 PI+ 211 1 244 234 0 0 0.43 -0.64 0.14 0.80 0.14 After the 1000 events requested have been generated, an analysis of the associated weight distribution and cross section is printed.