pythiaeRHIC/pythia/pygdir.f

0001
0002 C*********************************************************************
0003
0004 C...PYGDIR
0005 C...Evaluates the direct contribution, i.e. the C^gamma term,
0006 C...as needed in MSbar parametrizations.
0007 C...Adapted from SaSgam library, authors G.A. Schuler and T. Sjostrand.
0008
0009       SUBROUTINE PYGDIR(X,Q2,P2,Q02,XPGA)
0010
0011 C...Double precision and integer declarations.
0012       IMPLICIT DOUBLE PRECISION(A-H, O-Z)
0013       IMPLICIT INTEGER(I-N)
0014       INTEGER PYK,PYCHGE,PYCOMP
0015 C...Local array and data.
0016       DIMENSION XPGA(-6:6)
0017       DATA PMC/1.3D0/, PMB/4.6D0/, AEM2PI/0.0011614D0/
0018
0019 C...Reset output.
0020       DO 100 KFL=-6,6
0021         XPGA(KFL)=0D0
0022   100 CONTINUE
0023
0024 C...Evaluate common x-dependent expression.
0025       XTMP = (X**2+(1D0-X)**2) * (-LOG(X)) - 1D0
0026       CGAM = 3D0*AEM2PI*X * (XTMP*(1D0+P2/(P2+Q02)) + 6D0*X*(1D0-X))
0027
0028 C...d, u, s part by simple charge factor.
0029       XPGA(1)=(1D0/9D0)*CGAM
0030       XPGA(2)=(4D0/9D0)*CGAM
0031       XPGA(3)=(1D0/9D0)*CGAM
0032
0033 C...Also fill for antiquarks.
0034       DO 110 KF=1,5
0035         XPGA(-KF)=XPGA(KF)
0036   110 CONTINUE
0037
0038       RETURN
0039       END