* * $Id$ * * $Log$ * Revision 1.1.1.2 1996/10/30 08:27:44 cernlib * Version 7.04 * * Revision 1.1.1.1 1996/04/12 15:29:09 plothow * Version 7.01 * * #include "pdf/pilot.h" C Version 2 CTEQ distribution function in a parametrized form. C By: J. Botts, H.L. Lai, J.G. Morfin, J.F. Owens, J. Qiu, W.K. Tung & H. Weerts C C To avoid the proliferation of parton distribution functions, we recommend C that C these distributions should replace Version 1 CTEQ distributions for all C general C usage. The differences between the two sets of distributions, as briefly C described below, do not significantly affect most applications for C fixed-target C and hadron-collider applications. C C Both CTEQ1 and CTEQ2 distributions fit existing DIS, Drell-Yan and Direct C photon C data with excellent chi-squares. They represent two distinct ways to resolve C the inconsistency between CCFR and NMC measurements on F2 at small-x and the C neutrino dimuon measurements of s(x), as discovered by the CTEQ1 analysis: C in the CTEQ1 analysis, the F2 measurements of CCFR and NMC are taken C seriously, C leaving out the dimuon information on s(x); whereas in the CTEQ2 analysis, C the C latest CCFR NLO dimuon analysis of s(x) is used (within errors) as input C while C leaving out the small-x F2 data which conflict with this input. The small-x C behavior of the parton distributions are contrained in the latter case by the C newly released HERA data. For details, see our forthcoming paper. C C This file contains three versions of the same CTEQ2 parton distributions: C C Two "front-end" subprograms: C FUNCTION Ctq2OPf (Iset, Iparton, X, Q, Irt) C returns the PROBABILITY density for a GIVEN flavor; C SUBROUTINE Ctq2OPs (Iset, Pdf, XX, QQ, Irt) C returns an array of MOMENTUM densities for ALL flavors; C One lower-level subprogram: C FUNCTION Ctq2OPd (Iset, Iprtn, XX, QQ, Irt) C returns the MOMENTUM density of a GIVEN valence or sea distribution. C Supplementary functions to return the relevant QCD parameters and other C information concerning these distributions are also included (see below). C C Since this is an initial distribution of version 2, it is C useful for the authors to maintain a record of the distribution list in C case there are revisions or corrections. C In the interest of maintaining the integrity of this package, C please do not freely distribute this program package; instead, refer any C interested colleagues to direct their request for a copy to: C Botts@hades.ifh.de or Lai@cteq11.pa.msu.edu C If you have detailed questions concerning these CTEQ2 distributions, direct C inquires to Botts, Lai (see above) or Wu-Ki Tung (Tung@msupa.pa.msu.edu). C ------------------------------------------- C Detailed instructions follow. C Name convention for CTEQ distributions: CTEQnSx where C n : version number (currently n = 2) C S : factorization scheme label: = [M D L] for [MS-bar DIS LO] C resp. C x : special characteristics, if any C (e.g. S(F) for singular (flat) small-x, L for "LEP lambda value") C Explanation of functional arguments: C Iset is the set label; in this version, Iset = 1, 2, 3, 4, 5, 6 C correspond to the following CTEQ global fits: C cteq2M : best fit in the MS-bar scheme C cteq2MS : singular small-x C cteq2MF : flat small-x C cteq2ML : large lambda (Lambda(5) = 220 MeV) C cteq2L : best fit in Leading order QCD C cteq2D : best fit in the DIS scheme C Iprtn is the parton label (6, 5, 4, 3, 2, 1, 0, -1, ......, -6) C for (t, b, c, s, d, u, g, u_bar, ..., t_bar) C X, Q are the usual x, Q; C Irt is a return error code (see individual modules for explanation). C C --------------------------------------------- C --> QCD parameters for parton distribution set Iset can be obtained inside C the user's program by: C Dum = PrCtq2O C > (Iset, Iord, Ischeme, MxFlv, C > Alam4, Alam5, Alam6, Amas4, Amas5, Amas6, C > Xmin, Qini, Qmax, ExpNor) C where all but the first argument are output parameters. C They should be self-explanatory -- see details under ENTRY PrCtq2O. C Since the QCD Lambda value for the various sets are needed more often than C the other parameters in most applications, a special function C Wlamd2O (Iset, Iorder, Neff) is provided C which returns the lambda value for Neff = 4,5,6 effective flavors as well as C the order these values pertain to. C ---------------------------------------------- C The range of (x, Q) used in this round of global analysis is, approxi- C mately, 0.01 < x < 0.75 ; and 4 GeV^2 < Q^2 < 400 GeV^2 for fixed target C experiments and 0.0001 < x < 0.01 from first official data of HERA. C The range of (x, Q) used in the reparametrization of the QCD evolved C parton distributions is 10E-5 < x < 1 ; 1.6 GeV < Q < 1 TeV. The C functional form of this parametrization is: C A0 * x^A1 * (1-x)^A2 * (1 + A3 * x^A4) * [log(1+1/x)]^A5 C with the A'coefficients being smooth functions of Q. For heavy quarks, C a threshold factor is applied to A0 which simulates the proper Q-dependence C of the QCD evolution in that region according to the renormalization C scheme defined in Collins-Tung, Nucl. Phys. B278, 934 (1986). C Since this function is positive definite and smooth, it provides sensible C extrapolations of the parton distributions if they are called beyond C the original range in an application. There is no artificial boundaries C or sharp cutoff's. C ------------------------------------------------ FUNCTION Ctq2OPf (Iset, Iparton, X, Q, Irt) C This function returns the CTEQ parton distributions f^Iset_Iprtn/proton C --- the PROBABILITY density C (Iset, Iparton, X, Q): explained above; C Irt : return error code: see module Ctq2OPd for explanation. C IMPLICIT DOUBLE PRECISION (A-H, O-Z) C+SEQ, IMPDP. Ifl = Iparton JFL = ABS(Ifl) C Valence IF (Ifl.Eq.1 .or. Ifl.Eq.2) THEN VL = Ctq2OPd (Iset, Ifl, X, Q, Irt) ELSE VL = 0. ENDIF C Sea SEA = Ctq2OPd (Iset, -JFL, X, Q, Irt) C Full (probability) Distribution Ctq2OPf = (VL + SEA) / X Return C ************************* END