ISAJET/isasusy/ssf0.F

   1 #include "isajet/pilot.h"
   2       COMPLEX*16 FUNCTION SSF0(XQSQ,XM1,XM2)
   3 #if defined(CERNLIB_IMPNONE)
   4       IMPLICIT NONE
   5 #endif
   6       REAL XQSQ,XM1,XM2
   7       DOUBLE PRECISION QSQ,M1,M2,M1SQ,M2SQ,AQSQ,RE,XI,R
   8       DOUBLE PRECISION PI,T1,T2,BETA,XL,T
   9       DATA PI/3.14159265359D0/
  10       QSQ=XQSQ
  11       M1=XM1
  12       M2=XM2
  13       M1SQ=M1*M1
  14       M2SQ=M2*M2
  15       AQSQ=ABS(QSQ)
  16       IF(AQSQ.LT.1.D-6*(M1SQ+M2SQ)) THEN
  17         IF(ABS(M1-M2).LT.1.D-6*M1) THEN
  18           IF(M1SQ.LT.1.D-8) THEN
  19             RE=LOG(1.D-8)
  20           ELSE
  21             RE=LOG(M1SQ)+.5*(M2SQ/M1SQ-1.D0) -QSQ/(6.*M1SQ)
  22           ENDIF
  23         ELSE
  24           IF(M2SQ.LT.1.D-6*M1SQ) THEN
  25             RE=LOG(M1SQ)-1.D0
  26           ELSE IF(M1SQ.LT.1.D-6*M2SQ) THEN
  27             RE=LOG(M2SQ)-1.D0
  28           ELSEIF(M1SQ.GE.1.D-9*M2SQ) THEN
  29             RE=LOG(M1*M2)+(M1SQ+M2SQ)/(M1SQ-M2SQ)*LOG(M1/M2)-1.D0
  30      $      -QSQ*(.5*(M1SQ+M2SQ)-M1SQ*M2SQ*LOG(M2SQ/M1SQ)/(M2SQ-M1SQ))
  31      $      /(M1SQ-M2SQ)**2
  32           ENDIF
  33         ENDIF
  34         XI=0.D0
  35       ELSE
  36         IF(M1SQ.LT.1.D-6*AQSQ.OR.M2SQ.LT.1.D-6*AQSQ.OR.
  37      $  M1SQ+M2SQ.LT.1.D-5*AQSQ) THEN
  38           IF(M1SQ.LT.1.D-6*AQSQ) THEN
  39             R=M2SQ/QSQ
  40           ELSE
  41             R=M1SQ/QSQ
  42           ENDIF
  43           IF(ABS(R-1.D0).GT.1.D-6.AND.ABS(R).GT.1.D-6.AND.
  44      $    M1SQ+M2SQ.GT.1.D-5*AQSQ) THEN
  45             RE=LOG(R*QSQ)-2.D0+(1.D0-R)*LOG(ABS(1.D0-1.D0/R))
  46           ELSE
  47             RE=-2.D0+LOG(AQSQ)
  48           ENDIF
  49           IF(R.LT.1.D0.AND.R.GT.-1.D-10) THEN
  50             XI=-PI*(1.D0-R)
  51           ELSE
  52             XI=0.D0
  53           ENDIF
  54         ELSE
  55           T1=(M1-M2)*(M1-M2)
  56           T2=T1+4.0*M1*M2
  57           BETA=SQRT(ABS((1.D0-T1/QSQ)*(1.D0-T2/QSQ)))
  58           IF(QSQ.GT.T2.OR.QSQ.LT.T1) THEN
  59             XL=.5*BETA*LOG((QSQ*(1.D0+BETA)-M1SQ-M2SQ)/
  60      $      (QSQ*(1.D0-BETA)-M1SQ-M2SQ))
  61           ELSE
  62           T=M1SQ+M2SQ-QSQ
  63           IF(T.EQ.0.) T=1.D-10
  64             XL=BETA*ATAN(QSQ*BETA/T)
  65             IF(T.LT.0.D0) XL = XL + PI*BETA
  66           ENDIF
  67           RE=LOG(M1*M2)-(M1SQ-M2SQ)/QSQ*LOG(M2/M1)-2.D0+XL
  68           IF(QSQ.GT.T2) THEN
  69             XI=-PI*BETA
  70           ELSE
  71             XI=0.D0
  72           ENDIF
  73         ENDIF
  74       ENDIF
  75       SSF0=RE*(1.D0,0.D0)-XI*(0.D0,1.D0)
  76       RETURN
  77       END