PYTHIA/pythia/pyhfth.F

   1
   2 C*********************************************************************
   3
   4       FUNCTION PYHFTH(SH,SQM,FRATT)
   5
   6 C...Gives threshold attractive/repulsive factor for heavy flavour
   7 C...production.
   8       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
   9       COMMON/PYPARS/MSTP(200),PARP(200),MSTI(200),PARI(200)
  10       COMMON/PYINT1/MINT(400),VINT(400)
  11       SAVE /LUDAT1/
  12       SAVE /PYPARS/,/PYINT1/
  13
  14 C...Value for alpha_strong.
  15       IF(MSTP(35).LE.1) THEN
  16         ALSSG=PARP(35)
  17       ELSE
  18         MST115=MSTU(115)
  19         MSTU(115)=MSTP(36)
  20         Q2BN=SQRT(MAX(1.,SQM*((SQRT(SH)-2.*SQRT(SQM))**2+PARP(36)**2)))
  21         ALSSG=ULALPS(Q2BN)
  22         MSTU(115)=MST115
  23       ENDIF
  24
  25 C...Evaluate attractive and repulsive factors.
  26       XATTR=4.*PARU(1)*ALSSG/(3.*SQRT(MAX(1E-20,1.-4.*SQM/SH)))
  27       FATTR=XATTR/(1.-EXP(-MIN(50.,XATTR)))
  28       XREPU=PARU(1)*ALSSG/(6.*SQRT(MAX(1E-20,1.-4.*SQM/SH)))
  29       FREPU=XREPU/(EXP(MIN(50.,XREPU))-1.)
  30       PYHFTH=FRATT*FATTR+(1.-FRATT)*FREPU
  31       VINT(138)=PYHFTH
  32
  33       RETURN
  34       END