pythiaeRHIC/pythia/pyhfth.f

0001
0002 C*********************************************************************
0003
0004 C...PYHFTH
0005 C...Gives threshold attractive/repulsive factor for heavy flavour
0006 C...production.
0007
0008       FUNCTION PYHFTH(SH,SQM,FRATT)
0009
0010 C...Double precision and integer declarations.
0011       IMPLICIT DOUBLE PRECISION(A-H, O-Z)
0012       IMPLICIT INTEGER(I-N)
0013       INTEGER PYK,PYCHGE,PYCOMP
0014 C...Commonblocks.
0015       COMMON/PYDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
0016       COMMON/PYPARS/MSTP(200),PARP(200),MSTI(200),PARI(200)
0017       COMMON/PYINT1/MINT(400),VINT(400)
0018       SAVE /PYDAT1/,/PYPARS/,/PYINT1/
0019
0020 C...Value for alpha_strong.
0021       IF(MSTP(35).LE.1) THEN
0022         ALSSG=PARP(35)
0023       ELSE
0024         MST115=MSTU(115)
0025         MSTU(115)=MSTP(36)
0026         Q2BN=SQRT(MAX(1D0,SQM*((SQRT(SH)-2D0*SQRT(SQM))**2+
0027      &  PARP(36)**2)))
0028         ALSSG=PYALPS(Q2BN)
0029         MSTU(115)=MST115
0030       ENDIF
0031
0032 C...Evaluate attractive and repulsive factors.
0033       XATTR=4D0*PARU(1)*ALSSG/(3D0*SQRT(MAX(1D-20,1D0-4D0*SQM/SH)))
0034       FATTR=XATTR/(1D0-EXP(-MIN(50D0,XATTR)))
0035       XREPU=PARU(1)*ALSSG/(6D0*SQRT(MAX(1D-20,1D0-4D0*SQM/SH)))
0036       FREPU=XREPU/(EXP(MIN(50D0,XREPU))-1D0)
0037       PYHFTH=FRATT*FATTR+(1D0-FRATT)*FREPU
0038       VINT(138)=PYHFTH
0039
0040       RETURN
0041       END