ISAJET/code/ssgt.F

   1 #include "isajet/pilot.h"
   2         REAL FUNCTION SSGT(S,AMSQ,Z,I,J)
   3 C-----------------------------------------------------------------------
   4 C          Function for Sig(qqbar->z_i + z_j
   5 C-----------------------------------------------------------------------
   6 #if defined(CERNLIB_IMPNONE)
   7       IMPLICIT NONE
   8 #endif
   9 #include "isajet/sssm.inc"
  10 #include "isajet/sspar.inc"
  11         REAL S,AMSQ,K,Z,MZI,MZJ,RS,TPP,TPM,BTP,BTM
  12         INTEGER I,J,ITHI,ITHJ
  13 C
  14         MZI=ABS(AMZISS(I))
  15         MZJ=ABS(AMZISS(J))
  16         IF (AMZISS(I).LT.0.) THEN
  17           ITHI=1
  18         ELSE
  19           ITHI=0
  20         END IF
  21         IF (AMZISS(J).LT.0.) THEN
  22           ITHJ=1
  23         ELSE
  24           ITHJ=0
  25         END IF
  26         RS=SQRT(S)
  27         K=SQRT(S*S+(MZI**2-MZJ**2)**2-2*S*(MZI**2+MZJ**2))/
  28      $   2./RS
  29         TPP=S*S-(MZI**2-MZJ**2)**2-4*K*S**1.5*Z+4*K*K*S*Z*Z
  30         TPM=S*S-(MZI**2-MZJ**2)**2+4*K*S**1.5*Z+4*K*K*S*Z*Z
  31         BTP=(S-MZI**2-MZJ**2)/2.-RS*K*Z+AMSQ**2
  32         BTM=(S-MZI**2-MZJ**2)/2.+RS*K*Z+AMSQ**2
  33         SSGT=(TPP/BTP**2+TPM/BTM**2-8*(-1.)**(ITHI+ITHJ)*
  34      $   MZI*MZJ*S/BTM/BTP)/16.
  35         RETURN
  36         END