pyth_xsec.f

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       DOUBLE PRECISION FUNCTION pyth_xsec(dy,dx,dQ2,dF1,dF2)

       implicit none
        include "mc_set.inc"

*-----deklaration----------------------

       DOUBLE PRECISION dx, dq2,dy,debea    ! kinematic variables
       DOUBLE PRECISION dbrack   ! intermed. factor
       double precision emass2,alpha2,pi
       double precision df1,df2
! Load up some convenient variables
        pi=3.1415926d0
        alpha2=0.729735d-2**2
        emass2=masse**2
        debea = dble(mcset_enebeam)
! Check that the kinematics are reasonable
        if (dx.eq.0d0) then
          goto 999
        endif
       IF(dx.LE.0.d0.OR.dx.GE.1.d0.OR.
     1    dy.LE.0.d0.OR.dy.GE.1.d0.OR.dq2.le.0) then
          goto 999
       endif
! Determine the UNPOLARIZED xsec

       dbrack = (4.d0*pi*alpha2)/dq2**2
! ........ that's dSigma/dlogQ2/dlogy

       pyth_xsec = dbrack*(dy**2*(1-2d0*emass2/dq2)*df1+
     1                 (1-dy-dq2/(4d0*debea**2))*df2/dx)*dx*dq2

! Leave by the front door

       RETURN

! Leave by the back door

999    continue
       pyth_xsec = 0.0d0
       return
       end