ISAJET/code/qcdint.F

   1 #include "isajet/pilot.h"
   2       SUBROUTINE QCDINT(J0)
   3 C
   4 C          AUXILIARY ROUTINE FOR QCDINI.  GENERATE A NEW MASS FOR
   5 C          SPACELIKE PARTON J0.
   6 C
   7 #include "isajet/itapes.inc"
   8 #include "isajet/jetset.inc"
   9 #include "isajet/jwork.inc"
  10 #include "isajet/jwork2.inc"
  11 #include "isajet/qcdpar.inc"
  12 #include "isajet/primar.inc"
  13 C
  14       DIMENSION GAMS(13),FX0S(13)
  15       DATA CA/3./,CF/1.333333333/
  16 C
  17 C          FUNCTIONS -- USE DZMAX FOR PRECISION
  18       GQQ(Z,DZ)=CF*(-2.*ALOG(DZ)+Z*(-1.-.5*Z))
  19       GQG(Z)=CF*(+2.*ALOG(Z)+Z*(-2.+.5*Z))
  20       GGQ(Z)=(Z**3-(1.-Z)**3)/6.
  21       GGG(Z,DZ)=2.*CA*(ALOG(Z/DZ)+Z*(-2.+Z*(.5-Z/3.)))
  22       GBQQ(RZ,DZ)=CF*(2.*ALOG((1.+RZ)**2/DZ)+RZ*(-2.-2./3.*RZ**2))
  23       GBQG(RZ)=CF*(-4./RZ+RZ*(-4.+2./3.*RZ**2))
  24 C
  25       GLFORC(JET-10)=.FALSE.
  26       IDABS=IABS(JTYPE(J0))
  27       IF(JTYPE(J0).EQ.9) THEN
  28         ITYP=1
  29       ELSEIF(JTYPE(J0).GT.0) THEN
  30         ITYP=2*IDABS
  31       ELSE
  32         ITYP=2.*IDABS+1
  33       ENDIF
  34       IBEAM=JET-10
  35       AM0=ABS(PJSET(5,J0))
  36 1     T0=AM0**2
  37       X0=ZMIN
  38       ANF=3
  39       DO 110 I=4,6
  40       AMQ2=AMASS(I)**2
  41 110   ANF=ANF+T0/(AMQ2+T0)
  42       B0=11.-2.*ANF/3.
  43 C
  44 C          SET UP ANOMALOUS DIMENSIONS. ALSO USE THESE TO DETERMINE TYPE
  45 C          OF INCOMING PARTON (TO BE USED IN QCDINZ).
  46 C
  47 C          GLUON
  48       IF(IDABS.EQ.9) THEN
  49         AMQ=0.
  50         GAMG=GGG(ZMAX,DZMAX)-GGG(ZMIN,1.-ZMIN)
  51         GAMS(1)=GAMG
  52         FX0=STRUC(X0,T0,1,IDIN(IBEAM))
  53         FX0S(1)=FX0
  54         GAMFAC=(GBQG(SQRT(ZMAX))-GBQG(SQRT(ZMIN)))/FX0
  55         GAMQ=0.
  56         DO 210 IQ=2,13
  57         FX0S(IQ)=STRUC(X0,T0,IQ,IDIN(IBEAM))
  58         GAMS(IQ)=GAMFAC*FX0S(IQ)
  59 210     GAMQ=GAMQ+GAMS(IQ)
  60         GAM=GAMG+GAMQ
  61         AM1=CUTJET
  62 C
  63         TRY=RANF()
  64         SUM=0.
  65         DO 220 IQ=1,13
  66         SUM=SUM+GAMS(IQ)/GAM
  67         IF(SUM.LT.TRY) GO TO 220
  68         JIN(J0)=IQ
  69         FXTEST(J0)=FX0S(IQ)
  70         GO TO 300
  71 220     CONTINUE
  72 C
  73 C          LIGHT QUARK
  74       ELSEIF(IDABS.LE.3) THEN
  75         AMQ=AMASS(IDABS)
  76         GAMQ=GBQQ(SQRT(ZMAX),DZMAX)-GBQQ(SQRT(ZMIN),1.-ZMIN)
  77         FX0=STRUC(X0,T0,ITYP,IDIN(IBEAM))
  78         FXG=STRUC(X0,T0,1,IDIN(IBEAM))
  79         GAMFAC=FXG/FX0
  80         GAMG=GAMFAC*(GGQ(ZMAX)-GGQ(ZMIN))
  81         GAM=GAMQ+GAMG
  82         AM1=AMQ+CUTJET
  83 C
  84         IF(GAMQ/GAM.GT.RANF()) THEN
  85           JIN(J0)=ITYP
  86           FXTEST(J0)=FX0
  87         ELSE
  88           JIN(J0)=1
  89           FXTEST(J0)=FXG
  90         ENDIF
  91 C
  92 C          HEAVY QUARK -- SPECIAL TREATMENT NEEDED TO ALWAYS FORCE
  93 C          GL-->QK+QB BEFORE END OF EVOLUTION.
  94 C          USE SMALLER MASS FOR FORCED DECAYS TO PREVENT INFINITE LOOP.
  95       ELSE
  96         AMQ=AMASS(IDABS)
  97         THRESH=4.*AMQ**2*X0/(1.-X0)
  98         THRESH=(SQRT(THRESH)+CUTJET)**2
  99         IF(STRUC(X0,T0,ITYP,IDIN(IBEAM)).LE.0..OR.
 100      $  T0.LE.THRESH) THEN
 101           PJSET(5,J0)=-AM0*SQRT(RANF())-ALAM
 102           GLFORC(JET-10)=.TRUE.
 103           JDCAY(J0)=-2
 104           JIN(J0)=1
 105           FXTEST(J0)=1.
 106           RETURN
 107         ENDIF
 108         T1=SQRT(T0*THRESH)
 109 230     AM1=SQRT(T1)
 110         FX0=STRUC(X0,T1,ITYP,IDIN(IBEAM))
 111         IF(FX0.LE.0.) THEN
 112           T1=SQRT(T1*T0)
 113           GO TO 230
 114         ENDIF
 115         FXG=STRUC(X0,T1,1,IDIN(IBEAM))
 116         GAMFAC=FXG/FX0
 117         GAMQ=GQQ(ZMAX,DZMAX)-GQQ(ZMIN,1.-ZMIN)
 118         GAMG=GAMFAC*(GGQ(ZMAX)-GGQ(ZMIN))
 119         GAM=GAMQ+GAMG
 120 C
 121         IF(GAMQ/GAM.GT.RANF()) THEN
 122           JIN(J0)=ITYP
 123           FXTEST(J0)=FX0
 124         ELSE
 125           JIN(J0)=1
 126           FXTEST(J0)=FXG
 127         ENDIF
 128       ENDIF
 129 C
 130 C          LEADING-LOG MASS GENERATION.
 131 C
 132 300   GB=2.*GAM/B0
 133       IF(AM1.GT.ALAM.AND.AM0.GT.ALAM) THEN
 134         PROBL=GB*ALOG(ALOG(AM1/ALAM)/ALOG(AM0/ALAM))
 135       ELSE
 136         PROBL=0.
 137       ENDIF
 138       IF(PROBL.GT.0.) THEN
 139         PROB=1.
 140       ELSEIF(PROBL.GT.-50.) THEN
 141         PROB=EXP(PROBL)
 142       ELSE
 143         PROB=0.
 144       ENDIF
 145       IF(PROB.GT.RANF()) THEN
 146         IF(IDABS.LE.3.OR.IDABS.EQ.9) THEN
 147           PJSET(5,J0)=AMQ
 148           JDCAY(J0)=JPACK*J0+J0
 149           RETURN
 150         ELSEIF(AM0.LT.AM1+CUTJET) THEN
 151           PJSET(5,J0)=-SQRT(T0)
 152           GLFORC(JET-10)=.TRUE.
 153           JDCAY(J0)=-2
 154           JIN(J0)=1
 155           FXTEST(J0)=1
 156           RETURN
 157         ELSE
 158           AM0=AM1
 159           GO TO 1
 160         ENDIF
 161       ELSE
 162         POW=(1.-(1.-PROB)*RANF())**(1./GB)
 163         AMNEW=ALAM*(AM0/ALAM)**POW
 164         IF(AMNEW.GE.AM1) THEN
 165           PJSET(5,J0)=-AMNEW
 166           JDCAY(J0)=-2
 167           RETURN
 168         ELSEIF(IDABS.LE.3.OR.IDABS.EQ.9) THEN
 169           PJSET(5,J0)=AMQ
 170           JDCAY(J0)=JPACK*J0+J0
 171           RETURN
 172         ELSEIF(AM0.LT.AM1+CUTJET) THEN
 173           PJSET(5,J0)=-AM0*SQRT(RANF())-ALAM
 174           GLFORC(JET-10)=.TRUE.
 175           JDCAY(J0)=-2
 176           JIN(J0)=1
 177           FXTEST(J0)=1
 178           RETURN
 179         ELSE
 180           AM0=AM1
 181           GO TO 1
 182         ENDIF
 183       ENDIF
 184       END