pythiaeRHIC/erhic/pyth_xsec.f

0001        DOUBLE PRECISION FUNCTION pyth_xsec(dy,dx,dQ2,dF1,dF2)
0002
0003        implicit none
0004         include "mc_set.inc"
0005
0006 *-----DEKLARATION----------------------
0007
0008        DOUBLE PRECISION DX, DQ2,dy,DEBEA    ! kinematic variables
0009        DOUBLE PRECISION DBRACK   ! intermed. factor
0010        double precision emass2,alpha2,pi
0011        double precision df1,df2
0012 ! Load up some convenient variables
0013         pi=3.1415926d0
0014         alpha2=0.729735d-2**2
0015         emass2=masse**2
0016         DEBEA = dble(mcSet_EneBeam)
0017 ! Check that the kinematics are reasonable
0018         if (dx.eq.0D0) then
0019           goto 999
0020         endif
0021        IF(DX.LE.0.D0.OR.DX.GE.1.D0.OR.
0022      1    Dy.LE.0.D0.OR.Dy.GE.1.D0.OR.dq2.le.0) then
0023           goto 999
0024        endif
0025 ! Determine the UNPOLARIZED xsec
0026
0027        DBRACK = (4.D0*pi*alpha2)/dq2**2
0028 ! ........ that's dSigma/dlogQ2/dlogy
0029
0030        pyth_xsec = DBRACK*(dy**2*(1-2D0*emass2/dq2)*dF1+
0031      1                 (1-dy-dq2/(4D0*DEBEA**2))*dF2/dx)*dx*dQ2
0032
0033 ! Leave by the front door
0034
0035        RETURN
0036
0037 ! Leave by the back door
0038
0039 999    continue
0040        pyth_xsec = 0.0D0
0041        return
0042        end
0043