A new version of the Monte Carlo program HERWIG (version 6.1) is now
available, and can be obtained from the following web site:
http://hepwww.rl.ac.uk/theory/seymour/herwig/
This will temporarily be mirrored at CERN for the next few weeks:
http://home.cern.ch/~seymour/herwig/
More complete information on HERWIG can be found in the publication
G. Marchesini, B.R. Webber, G. Abbiendi, I.G. Knowles, M.H. Seymour
and L. Stanco, Computer Phys. Commun. 67 (1992) 465 and also in the
documentation for the previous version (5.9), which are available at
the same site, together with other useful files and information.
Here we merely give the new features relative to 5.9.
If you use HERWIG, please refer to it something along the lines of:
HERWIG 6.1, hep-ph/9912396; G. Marchesini, B.R. Webber, G. Abbiendi,
I.G. Knowles, M.H. Seymour and L. Stanco,
Computer Phys. Commun. 67 (1992) 465.
*** NEW FEATURES OF THIS VERSION ***
*---------------------------------------------------------------*
| The main new features are: supersymmetric processes (both |
| R-parity conserving & violating) in hadron-hadron collisions; |
| new e+e- to four jets process; matrix element corrections to |
| top decay and Drell-Yan processes; new soft underlying event |
| options; updates to default particle data tables; new LaTeX & |
| html printout options. |
*---------------------------------------------------------------*
* [N.B. Default values for input variables shown in square brackets.]
* All R-parity conserving SUSY two-to-two processes in hadron-hadron
collisions have been added. Their process numbers are:
+-------+----------------------------------------------------------+
| IPROC | Process |
+-------+----------------------------------------------------------+
| 3000 | 2 parton to 2 sparticles: the sum of 3010,3020 and 3030 |
| 3010 | 2 parton to 2 spartons |
| 3020 | 2 parton to 2 gauginos |
| 3030 | 2 parton to 2 sleptons |
+-------+----------------------------------------------------------+
Further details of the inclusion of superpartners and their decays
are given below.
Additional processes for the SUSY two Higgs doublet model are
currently under test and will be released shortly.
* All R-parity violating SUSY two-to-two processes via resonant
sleptons and squarks in hadron collisions have been added. Their
process numbers are:
+-------+----------------------------------------------------------+
| IPROC | Processes derived from the LQD term in the superpotential|
+-------+----------------------------------------------------------+
| 4000 | The sum of 4010,4020,4040 and 4050 |
| 4010 | Neutralino lepton production (all neutralinos) |
| 401i | As 4010 but only the ith neutralino |
| 4020 | Chargino lepton production (all charginos) |
| 402i | As 4020 but only the ith chargino |
| 4040 | Slepton W/Z production |
| 4050 | Slepton Higgs production |
+-------+----------------------------------------------------------+
| 4060 | Sum of 4070 and 4080 |
| 4070 | quark-antiquark production via LQD |
| 4080 | lepton production via LLE and LQD |
+=======+==========================================================+
| IPROC | Processes derived from the UDD term in the superpotential|
+-------+----------------------------------------------------------+
| 4100 | The sum of 4110, 4120, 4130, 4140 and 4150 |
| 4110 | Neutralino quark production (all neutralinos) |
| 411i | As 4110 but only the ith neutralino |
| 4120 | Chargino quark production (all charginos) |
| 412i | As 4120 but only the ith chargino |
| 4130 | Gluino quark production |
| 4140 | Squark W/Z production |
| 4150 | Squark Higgs production |
+-------+----------------------------------------------------------+
| 4160 | quark-quark production |
+-------+----------------------------------------------------------+
In addition the R-parity violating decays of all superpartners is
included.
* A new process describing electron-positron annihilation to four jets
has been added. This has IPROC=600+IQ, where a non-zero value for IQ
guarantees production of quark flavour IQ whilst IQ=0 corresponds to
the natural flavour mix. IPROC=650+IQ is as above but without those
terms in the matrix element which orient the event w.r.t. the lepton
beam direction. The matrix elements are based on those of Ellis Ross
& Terrano with orientation terms from Catani & Seymour. The soft and
collinear divergences are avoided by imposing a minimum y-cut, Y4JT
[.01], on the initial 4 partons. The interjet distance is calculated
using either the Durham or JADE metrics. This choice is governed by
the logical variable DURHAM [.TRUE.]. Note that parameterizations of
the volume of four-body phase space are used: these are accurate up
to a few percent for y-cut values less than 0.14. Note, also that
the phase space is for massless partons, as are the matrix elements,
though a mass threshold cut is applied. Finally, the matrix elements
for the q-qbar-g-g & q-qbar-q-qbar (same flavour quark) final states
receive contributions from 2 colour flows each, the treatment of the
interference terms being controlled by the array IOP4JT:
q-qbar-g-g case:
IOP4JT(1)=0 neglect, =1 extreme 2341; =2 extreme 3421 [0]
q-qbar-q-qbar (identical quark flavour) case:
IOP4JT(2)=0 neglect, =1 extreme 4123; =2 extreme 2143 [0]
The scale EMSCA for the parton showers is set equal to SQRT(s*ymin)
where ymin is the least distance, according to the selected metric,
between any two partons.
* Matrix element corrections to the simulation of top quark decays and
Drell-Yan processes are now available using the same general method
as already implemented for e+e- annihilation and DIS. If HARDME
[.TRUE.] then fill the missing phase-space (`dead zone') using the
exact 1st-order M.E. result (`hard corrections'). If SOFTME
[.TRUE.] then correct emissions in the already-populated region of
phase space using the exact amplitude for every emission that is
capable of being the hardest so far (`soft corrections').
- For t -> bW decays the routine HWBTOP implements hard corrections.
HWBRAN has been modified to implement the soft corrections to top
decays. Since the dead zone includes part of the soft singularity
a cutoff is required: only gluons with energy above GCUTME [2 GeV]
(in the top rest frame) are corrected. Physical quantities are not
strongly dependent on GCUTME in the range 1 to 5 GeV. For details
see:
G. Corcella and M.H. Seymour, Phys. Lett. B442 (1998) 417.
- For the Drell-Yan process the routine HWBDYP implements the hard
corrections whilst HWSBRN has been modified to implement the soft
corrections to the initial state radiation. For details see:
G. Corcella and M.H. Seymour, hep-ph/9908338.
* The parameters of the model used for soft interactions are now
available to the user for modification. The model is based on the
minimum-bias event generator of the UA5 Collaboration, which starts
from a parametrization of the pbar p inelastic charged multiplicity
distribution as a negative binomial. The parameters are as follows
(default parameter values are the UA5 ones used in previous
versions):
+-------+---------------------------+---------+
| Name | Description | Default |
+-------+---------------------------+---------+
| PMBN1 | a in = a*S^b+c | 9.11 |
| PMBN2 | b in = a*S^b+c | 0.115 |
| PMBN3 | c in = a*S^b+c | -9.50 |
| | | |
| PMBK1 | a in 1/k = a*log_e(S)+b | 0.029 |
| PMBK2 | b in 1/k = a*log_e(S)+b | -0.104 |
| | | |
| PMBM1 | a in (M-m_1-m_2-a)e^{-bM} | 0.4 |
| PMBM2 | b in (M-m_1-m_2-a)e^{-bM} | 2.0 |
| | | |
| PMBP1 | p_t slope for d,u | 5.2 |
| PMBP2 | p_t slope for s,c | 3.0 |
| PMBP3 | p_t slope for qq | 5.2 |
+-------+---------------------------+---------+
The first three parametrize the mean charged multiplicity at
c.m. energy \sqrt{s} as indicated. The next two specify the
parameter k in the negative binomial charged multiplicity
distribution. The parameters PMBM1 and PMBM2 describe the
distribution of cluster masses M in the soft collision. These soft
clusters are generated with a flat rapidity distribution with
gaussian shoulders. The transverse momentum distribution of soft
clusters has the form
P(p_t)\propto p_t\exp(-b\sqrt{p_t^2+M^2})
where the slope parameter b depends as indicated on the flavour of
the quark or diquark pair created when the cluster was produced.
As an option, for underlying events the value of \sqrt{s} used to
choose the multiplicity n may be enhanced by a parameter ENSOF to
allow for an enhanced underlying activity in hard events. The actual
charged multiplicity is then taken to be n plus the sum of the
moduli of the charges of the colliding hadrons or clusters.
* There have been a number of additions/changes to the default hadrons
included via HWUDAT. Here the identification of hadrons follows the
PDG ('98 edition) table 13.2 with numbering according to section 31.
New isoscalars states have been added to try to complete the 1^3D_3,
1^1D_2 and 1^3D_1 multiplets:
IDHW RNAME IDPDG IDHW RNAME IDPDG
---- ----- ----- ---- ----- -----
395 OMEGA_3 227 396 PHI_3 337
397 ETA_2(L) 10225 398 ETA_2(H) 10335
399 OMEGA(H) 30223
Also the following states have been re-identified/replaced:
IDHW RNAME IDPDG IDHW RNAME IDPDG
---- ----- ----- ---- ----- -----
57 FH_1 20333
293 F0P0 9010221 294 FH_00 10221
62 A_0(H)0 10111 290 A_00 9000111
63 A_0(H)+ 10211 291 A_0+ 9000211
64 A_0(H)- -10211 292 A_0- -9000211
The f_1(1420) state completely replaces the f_1(1520) in the 1^3P_0
multiplet, taking over 57. The f_0(1370) (294) replaces the f_0(980)
(293) in the 1^3P_0 multiplet; the latter is retained as it appears
in the decays of several other states. The new a_0(1450) states (62
-64) replace the three old a_0(980) states (290 - 292) in the 1^3P_0
multiplet; the latter are kept, as they appear in f_1(1285) decays.
By default production of the f_0(980) and a_0(980) states in cluster
decays is vetoed.
Also, the PDG numbers for the remnant particles have been changed to
98 for REMG and 99 for REMN.
* Since version 6.1 contains a large number of supersymmetry processes
several new particles have been added.
Extra scalar bosons for the two Higgs Doublet (SUSY) scenario:
IDHW RNAME IDPDG IDHW RNAME IDPDG
---- ----- ----- ---- ----- -----
203 HIGGSL0 26 206 HIGGS+ 37
204 HIGGSH0 35 207 HIGGS- -37
205 HIGGSA0 36
Note that the lighter neutral scalar (203) is given the non-standard
PDG number 26, in order to distinguish it from the minimal SM Higgs,
PDG number 25.
Extra sfermions and gauginos for SUSY scenarios:
IDHW RNAME IDPDG IDHW RNAME IDPDG
---- ----- ----- ---- ----- -----
401 SSDL 1000001 413 SSDR 2000001
| | | | | |
406 SST1 1000006 418 SST2 2000006
407 SSDLBR -1000001 419 SSDRBR -2000001
| | | | | |
412 SST1BR -1000006 424 SST2BR -2000006
425 SSEL- 1000011 437 SSER- 2000011
| | | | | |
430 SSNUTL 1000016 442 SSNUTR 2000016
431 SSEL+ -1000011 443 SSER+ -2000011
| | | | | |
436 SSNUTLBR -1000016 448 SSNUTRBR -2000016
449 GLUINO 1000021 454 CHGINO1+ 1000024
450 NTLINO1 1000022 455 CHGINO2+ 1000037
451 NTLINO2 1000023 456 CHGINO1 -1000024
452 NTLINO3 1000025 457 CHGINO2 -1000037
453 NTLINO4 1000035 458 GRAVTINO 1000039
The implementation of SUSY is discussed more fully below. Note that
the default masses of the SUSY particles are zero and that they have
no decay modes. Before a SUSY process can be simulated you must load
the appropriate masses and decay modes generated using ISAWIG (see
below) or an equivalent program.
These new states don't interfere with the user's ability to add new
particles as previously described.
* It is now possible to create particle property and event listings in
any combination of 3 formats - standard ASCII, LaTeX or html. These
options are controlled by the new, logical variables PRNDEF [.TRUE.]
PRNTEX [.FALSE.] and PRNWEB [.FALSE.]. The ASCII output is directed
to stout (screen / log file) as in previous versions. When a listing
of particle properties is requested (IPRINT.GE.2 or HWUDPR is called
explicitly) then the following files are produced:
If (PRNTEX): HW_decays.tex
If (PRNWEB): HW_decays/index.html
/PART0000001.html etc.
The HW_decays.tex file is written to the working directory whilst
the many **.html files appear in the sub-directory HW_decays/ which
must have been created previously. Paper sizes and offsets for the
LaTeX output are stored at the top of the block data file HWUDAT:
they may need modifying to suit a particular printer. When event
listings are requested (NEVHEP.LE.MAXPR.NE.0 or HWUEPR is called
explicitly) the following files are created in the current working
directory:
If (PRNTEX): HWEV_*******.tex where *******=0000001 etc.
If (PRNWEB): HWEV_*******.html is the event number
Note the .html file automatically makes links to the index.html file
of particle properties assumed to be in the HW_decays sub-directory.
A new integer variable NPRFMT [1] has been introduced to control how
many significant figures are shown in each of the 3 event outputs.
Basically NPRFMT=1 gives short compact outputs whilst NPRFMT=2 gives
long formats.
Note that all the LaTeX files use the package longtable.sty to
format the tables. Also if NPRFMT=2 or PRVTX=.TRUE. then the LaTeX
files are designed to be printed in landscape mode.
* There were previously some inconsistencies and ambiguities in our
conventions for the mixing of flavour `octet' and `singlet' mesons.
They are now:
Multiplet Octet Singlet Mixing Angle
--------- ----- ------- ------------
1^1S_0 eta eta' ETAMIX=-23.
1^3S_1 phi omega PHIMIX=+36.
1^1P_1 h_1(1380) h_1(1170) H1MIX =ANGLE
1^3P_0 MISSING f_0(1370) F0MIX =ANGLE
1^3P_1 f_1(1420) f_1(1285) F1MIX =ANGLE
1^3P_2 f'_2 f_2 F2MIX =+26.
1^1D_2 eta_2(1645) eta_2(1870) ET2MIX=ANGLE
1^3D_1 MISSING omega(1600) OMHMIX=ANGLE
1^3D_3 phi_3 omega_3 PH3MIX=+28.
After mixing the quark content of the physical states is given, in
terms of the mixing angle, theta, by:
(ddbar+uubar)/sqrt(2) ssbar
--------------------- -----
Octet: cos(theta+theta_0) -sin(theta+theta_0)
Singlet: sin(theta+theta_0) cos(theta+theta_0)
where theta_0=ATAN(SQRT(2)). Hence, using the default value of
ANGLE=ATAN(1/SQRT(2))*180/ACOS(-ONE) for theta gives ideal mixing,
that is, the `octet' state = ssbar and the `singlet' =
(ddbar+uubar)/sqrt(2). This choice is important to avoid large
isospin violations in the 1^3P_0 and 1^3D_1 multiplets in which the
octet member is unknown.
* A new treatment of the colour interference terms in matrix elements
has been introduced in this version. A non-planar, interference term
is now shared between the planar terms corresponding to well defined
colour flows in proportion to the size of the planar terms. Existing
two-to-two QCD processes which have been affected are:
Light Quarks Heavy Quarks
============ ============
Process IHPRO Process IHPRO
------- ----- ------- -----
q +q --> q +q 1,2 Q +g --> Q +g 10,11
q +qbar --> q +qbar 5,6 Qbar+g --> Qbar+g 21,22
qbar+q --> qbar+q 13,14 g +Q --> g +Q 23,24
qbar+qbar --> qbar+qbar 18,19 g +Qbar --> g +Qbar 25,26
g +g --> Q +Qbar 27,28
The present and previous treatments of the interference term are the
same for the other two-to-two QCD processes which remain unaffected.
This new procedure has been adopted for all the SUSY QCD processes.
For details see: K. Odagiri, JHEP 10 (1998) 006
* A new process, direct gamma-gamma to charged particle pairs has been
added. This has IPROC=16000+IQ: if IQ=1-6 then only quark flavour IQ
is produced, if IQ=7,8 or 9 then only lepton flavour e, mu or tau is
produced and if IQ=10 then only W pairs are produced: in these cases
particle masses effects are included. Whilst if IQ=0 the natural mix
of quark pairs are produced using massless MEs but including a mass
threshold cut. The range of allowed transverse momenta is controlled
by PTMIN & PTMAX as usual.
* A new package ISAWIG has been created to work with ISAJET to produce
a file of the SUSY particle masses, lifetimes and decay modes which
can be read in by HERWIG.
This package takes the outputs of the ISAJET SUGRA or general MSSM
programs and produces a data file in a format that can be read in by
the HWISSP subroutine described below.
In addition to the decay modes included in the ISAJET package ISAWIG
allows for the possibility of violating R-parity and includes the
calculation of all 2-body squark and slepton, and 3-body gaugino and
gluino R-parity violating decay modes.
* A new subroutine HWISSP has been added to read the file of particle
properties produced by the ISAWIG program. In principle the user can
produce a similar file provided that the correct format is used. The
format should be as follows.
First the SUSY particle and top quark masses and lifetimes are given
as, for example:
65
401 927.3980 0.74510E-13
402 925.3307 0.74009E-13
....etc.
That is,
NSUSY=Number of SUSY+top particles
IDHW, RMASS(IDHW) & RLTIM(IDHW)
repeated NSUSY times.
Next each particle's decay modes together with their branching
ratios and matrix element codes are given as, for example:
6
401 0.18842796E-01 0 450 1 0 0 0
| | | | | | | |
401 0.32755006E-02 0 457 2 0 0 0
6
402 0.94147678E-02 0 450 2 0 0 0
....etc.
That is,
Number of decay modes for a given particle (IDK)
IDK(*), BRFRAC(*), NME(*) & IDKPRD(1-5,*)
repeated for each mode.
Repeated for each particle (NSUSY times).
The order in which the decay products appear is significant: this is
important inorder to obtain appropriate showering and hadronization.
The correct ordering for each decay mode is indicated below.
+----------+------------------------+------------------------------+
| Decaying | Type of Mode | Order of Decay Products: |
| Particle | | 1st | 2nd | 3rd |
+----------+------------------------+---------+---------+----------+
| Top | 2 body to Higgs | Higgs | Bottom | |
| +------------------------+---------+---------+----------+
| | 3 body via Higgs/W | quarks or leptons | Bottom |
| | | from W/Higgs | |
+----------+------------------------+---------+---------+----------+
| Gluino | 2 body modes: | | | |
| | without gluon | any order | |
| | with gluon | gluon | colour | |
| | | | neutral | |
| +------------------------+---------+---------+----------+
| | 3 body modes: | colour | q or qbar |
| | R-parity conserved | neutral | |
+----------+------------------------+---------+---------+----------+
| Squark/ | 2 body modes: | | | |
| Slepton | Gaugino/Gluino | Gaugino | quark | |
| | Quark/Lepton | Gluino | lepton | |
| +------------------------+---------+---------+----------+
| | 3 body modes: |sparticle| particles from |
| | Weak | | W decay |
+----------+------------------------+---------+---------+----------+
| Squark | 2 body modes: | | | |
| | Lepton Number Violated | quark | lepton | |
| | Baryon Number Violated | quark | quark | |
+----------+------------------------+---------+---------+----------+
| Slepton | 2 body modes: | q or qbar | |
| | Lepton Number Violated | | | |
+----------+------------------------+---------+---------+----------+
| Higgs | 2 body modes: | | | |
| | (s)quark-(s)qbar | (s)q or (s)qbar | |
| | (s)lepton-(s)lepton | (s)l or (s)lbar | |
| +------------------------+---------+---------+----------+
| | 3 body modes: | colour | q or qbar |
| | | neutral | l or lbar |
+----------+------------------------+---------+---------+----------+
| Gaugino | 2 body modes: | | | |
| | squark-quark | q or sq | |
| | slepton-lepton | l or sl | |
| +------------------------+---------+---------+----------+
| | 3 body modes: | colour | q or qbar |
| | R-parity conserved | neutral | l or lbar |
+----------+------------------------+---------+---------+----------+
| Gaugino/ | 3 body modes: | particles in the order i,j,k |
| Gluino | R-parity violating | |
+----------+------------------------+---------+---------+----------+
A new matrix element code has been added for these decays:
NME = 300 3 body R-parity violating gaugino and gluino decays
in addition, an extra matrix element code has been reserved for use
in a forthcoming version:
NME = 200 3 body top quark via charged Higgs
The indices i,j,k in R-parity violating gaugino/gluino decays refer
to the ordering of the indices in the R-parity violating couplings
in the superpotential. The convention is as in:
H.Dreiner, P.Richardson and M.H.Seymour, hep-ph/9912407.
Next a number of parameters derived from the SUSY Lagrangian must be
given. These are: the ratio of Higgs VEVs, tan(beta), and the scalar
Higgs mixing angle, alpha; the mixing parameters for the Higgses,
gauginos and the sleptons; the trilinear couplings; and the Higgsino
mass parameter mu.
Finally the logical variable RPARTY should be set: if FALSE then
R-parity is violated, and the R-parity violating couplings must also
be supplied, otherwise not.
Details of the FORMAT statements employed can be found by examining
the subroutine HWISSP.
The integer argument in the call to HWISSP(N) gives the unit number
to be read from. If the data is stored in a `fort.N' file no further
action is required but if the data is to be read from a file named
`fname.dat' then appropriate OPEN and CLOSE statements must be added
by hand:
OPEN(UNIT=N,FORM='FORMATTED',STATUS='UNKNOWN',FILE='fname.dat')
CALL HWISSP(N)
CLOSE(UNIT=N)
A number of sets of SUSY parameter files, produced using ISAWIG, for
the standard LHC SUGRA and GMSB points are available from the HERWIG
home page: http://hepwww.rl.ac.uk/theory/seymour/herwig/
* A large number of changes have been made to enable SUSY processes to
be included in hadron-hadron collisions. The main changes are:
- The subroutine HWDHQK has been replaced by HWDHOB which does both
heavy quark and SUSY particle decays.
- The subroutines HWBCON HWCGSP & HWCFOR have been adapted to handle
the colour connections found in normal SUSY decays.
- The subroutine HWBRCN has been included to deal with the inter-jet
colour connections arising in R-parity violating SUSY. Also HWCBVI
HWCBVT and HWCBCT have been added to handle the hadronization of
baryon number violating SUSY decays and processes. If the variable
RPARTY=.TRUE. [default] then the old HWBCON colour connection code
is used else the new HWBRCN
* The option of separate treatments for `light' and b-quark containing
clusters are now available. The 3 variables, PSPLT (which controls
the mass spectrum of the fragments in heavy cluster splitting) CLDIR
(which controls whether perturbatively produced (anti-)quarks retain
some knowledge of their direction in cluster decays to hadrons) and
CLSMR (which defines to what extent the hadron and constituent quark
directions are aligned), have been made two dimensional.
ARRAY(1) controls clusters that do NOT contain a b quark
ARRAY(2) controls clusters that do contain a b quark
[ Default ARRAY(1)=ARRAY(2) equivalent to earlier versions. ]
* A new variable EFFMIN [1E-3] has been introduced, it allows the user
to set the minimum acceptable efficiency for event generation.
* All hadron & lepton masses are now given to five significant figures
whenever possible.
* The treatment of the perturbative g --> qqbar vertex in the partonic
showers has been improved. The total rate is unchanged, but the
angular distribution now covers the full range, rather than being
confined to the angular-ordered region as before.
* The treatment of the intrinsic transverse momentum of partons in an
incoming hadron has been improved. It is now chosen before the
initial state cascade is performed, and is held fixed even if the
generated cascade is rejected. This removes a correlation between
the amount of perturbative and non-perturbative transverse momentum
generated that existed before.
* Space-time positioning of clusters is now smeared according to a
Gaussian distribution of width 1/(cluster mass).
* For e+e- processes with ISR a check was added requiring TMNISR to be
greater than the light quark threshold.
* The treatment of the W resonance in top decays has been improved.
* The common block file HERWIG61.INC has had many new variables added,
these are listed at the top of the file.
* Corrections for bugs have been made affecting the following:
- eta-eta' mixing: the parameterization was nonstandard (see above).
- 4/5 body phase space generation: was not flat - affected resonance
decays only.
- Drell-Yan: the overall normalization was too small by a factor 2/3
also the t-channel contribution to q-qbar-> q-qbar was incorrectly
normalized.
- HWHV1J: the normalization of Z+jet production rate was a factor 4
too small; there was an incorrect correlation between the (signed)
W and jet rapidities; the treatment of the W/Z Breit-Wigner lead a
normalization error by a factor 3/pi.
- HWHWPR: there was an overall normalization error of (M_ff'/M_w)^2,
this only affected the line shape and normalization for the t-bbar
final state for which M_ff' is large.
- B_d/_s mixing: an incorrect formula was used.
- VMIN2: the effective cut-off on the space-time distances travelled
by light partons in a shower was incorrectly implemented. Also its
default value has been increased to [0.1], which affects the
colour reconnection probability.
- A number of fixes to improve safety against overflowing the HEPEVT
common block.
- Fix to the underlying event to prevent errors with heavy quarks.
- HWMODK/HWIODK: a number of corrections were made and the code made
more robust.
- HWURES: the minimum threshold for the decay of diquark-antidiquark
clusters was incorrectly set.
- The calculation of the top lifetime has been corrected and the QCD
corrections included - this only affects the treatment of colour
reconnection.
- The space-time positioning of clusters sometimes led to them being
produced outside the forward lightcone. This has been rectified.
As usual, if you wish to be removed from the HERWIG mailing list, or
if you know someone who wants to be added, please let one of us
know.
Mike Seymour, Bryan Webber, Ian Knowles, Peter Richardson, Kosuke
Odagiri, Stefano Moretti, Gennaro Corcella, Pino Marchesini
CERN, Edinburgh, Oxford, RAL, Rochester, Milano, etc,
16th December 1999.