pyhfth.f

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C*********************************************************************
 
C...PYHFTH
C...Gives threshold attractive/repulsive factor for heavy flavour
C...production.
 
      FUNCTION pyhfth(SH,SQM,FRATT)
 
C...Double precision and integer declarations.
      IMPLICIT DOUBLE PRECISION(a-h, o-z)
      IMPLICIT INTEGER(i-n)
      INTEGER pyk,pychge,pycomp
C...Commonblocks.
      common/pydat1/mstu(200),paru(200),mstj(200),parj(200)
      common/pypars/mstp(200),parp(200),msti(200),pari(200)
      common/pyint1/mint(400),vint(400)
      SAVE /pydat1/,/pypars/,/pyint1/
 
C...Value for alpha_strong.
      IF(mstp(35).LE.1) THEN
        alssg=parp(35)
      ELSE
        mst115=mstu(115)
        mstu(115)=mstp(36)
        q2bn=sqrt(max(1d0,sqm*((sqrt(sh)-2d0*sqrt(sqm))**2+
     &  parp(36)**2)))
        alssg=pyalps(q2bn)
        mstu(115)=mst115
      ENDIF
 
C...Evaluate attractive and repulsive factors.
      xattr=4d0*paru(1)*alssg/(3d0*sqrt(max(1d-20,1d0-4d0*sqm/sh)))
      fattr=xattr/(1d0-exp(-min(50d0,xattr)))
      xrepu=paru(1)*alssg/(6d0*sqrt(max(1d-20,1d0-4d0*sqm/sh)))
      frepu=xrepu/(exp(min(50d0,xrepu))-1d0)
      pyhfth=fratt*fattr+(1d0-fratt)*frepu
      vint(138)=pyhfth
 
      RETURN
      END