HIJING/hijing1_36/gphoton.F

   1 * $Id$
   2 C
   3 C
   4 C
   5         FUNCTION GPHOTON(Y1,Y2,PT2)
   6         IMPLICIT REAL*8 (A-H,O-Z)
   7 #include "hiparnt.inc"
   8         DIMENSION F(2,7)
   9         SAVE
  10         XT=2.0*DSQRT(PT2)/HINT1(1)
  11         X1=0.50*XT*(DEXP(Y1)+DEXP(Y2))
  12         X2=0.50*XT*(DEXP(-Y1)+DEXP(-Y2))
  13         Z=DSQRT(1.D0-XT**2/X1/X2)
  14         SS=X1*X2*HINT1(1)**2
  15         T=-(1.0-Z)/2.0
  16         U=-(1.0+Z)/2.0
  17         AF=3.0
  18         DLAM=HIPR1(15)
  19         APH=12.0*3.1415926/(33.0-2.0*AF)/DLOG(PT2/DLAM**2)
  20         APHEM=1.0/137.0
  21 C
  22         CALL PARTON(F,X1,X2,PT2)
  23 C
  24         G11=-(U**2+1.0)/U/3.0*F(1,7)*(4.0*F(2,1)+4.0*F(2,2)
  25      &      +F(2,3)+F(2,4)+F(2,5)+F(2,6))/9.0
  26         G12=-(T**2+1.0)/T/3.0*F(2,7)*(4.0*F(1,1)+4.0*F(1,2)
  27      &      +F(1,3)+F(1,4)+F(1,5)+F(1,6))/9.0
  28         G2=8.0*(U**2+T**2)/U/T/9.0*(4.0*F(1,1)*F(2,2)
  29      &     +4.0*F(1,2)*F(2,1)+F(1,3)*F(2,4)+F(1,4)*F(2,3)
  30      &     +F(1,5)*F(2,6)+F(1,6)*F(2,5))/9.0
  31 C
  32         GPHOTON=(G11+G12+G2)*HIPR1(23)*3.14159*APH*APHEM/SS**2
  33         RETURN
  34         END