ISAJET/code/estruc.F

   1 #include "isajet/pilot.h"
   2       FUNCTION ESTRUC(X,QS)
   3 C
   4 C     THIS IS ELECTRON PARTON DISTRIBUTION FUNCTION;
   5 C     SAME AS USED IN PYTHIA; NOTE! ESTRUC=0 FOR X>.999999
   6 C
   7 #if defined(CERNLIB_IMPNONE)
   8       IMPLICIT NONE
   9 #endif
  10       REAL ESTRUC,AL,PI,AME,QS,X,BT,XM,T,A,B
  11 C
  12       AL=1./128.
  13       PI=4*ATAN(1.)
  14       AME=.511E-3
  15       BT=2*AL/PI*(LOG(QS/AME/AME)-1.)
  16 C     KLEISS/SJOSTRAND PRESCRIPTION
  17 C      IF (X.LE..9999) THEN
  18 C        ESTRUC=BT/2.*(1.-X)**(BT/2.-1.)
  19 C      ELSE IF (X.LE..999999.AND.X.GT..9999) THEN
  20 C        ESTRUC=100.**(BT/2.)/(100.**(BT/2.)-1.)*BT/2.*
  21 C    $          (1.-X)**(BT/2.-1.)
  22 C      ELSE
  23 C        ESTRUC=0.
  24 C      END IF
  25 C     FADIN-KURAEV/DREES PRESCRIPTION
  26       XM=.998
  27       IF(X.GT.XM) THEN
  28         T = (1.+.375*BT)*(1.-XM)**(BT/2.)
  29         A = ((1.0-BT/2.)*T
  30      &        -.25*BT*(1.5-XM*(1.+XM/2.)))/(1.-XM)
  31      &        +.25*BT*(1.0+XM)
  32         A = 2*A/(1.-XM)
  33         B = .5*BT*T/(1.-XM) - .25*BT*(1.+XM) - A*XM
  34         ESTRUC = A*X+B
  35       ELSE
  36         ESTRUC = .5*BT*((1.-X)**(.5*BT-1.)) * (1.+.375*BT)
  37      &            -.25*BT*(1.+X)
  38       ENDIF
  39       RETURN
  40       END