ISAJET/code/qcdt.F

   1 #include "isajet/pilot.h"
   2       SUBROUTINE QCDT(J)
   3 C
   4 C          Auxiliary routine for QCDJET. Calculate ZC and store in
   5 C          ZZC(J).  Generate new mass with ZC and store in PJSET(5,J).
   6 C
   7 C          Must include 1/2 symmetry factor in GAMGG. No fix is needed
   8 C          in QCDZ since GAMGG+2*GAMQQ is used as the normalization.
   9 C
  10 C          Include GM, W+, W-, and Z0 radiation.
  11 C
  12 C          Ver 7.20: Anomalous dimensions were coded incorrectly!
  13 C
  14 #if defined(CERNLIB_IMPNONE)
  15       IMPLICIT NONE
  16 #endif
  17 #include "isajet/itapes.inc"
  18 #include "isajet/jetset.inc"
  19 #include "isajet/jwork.inc"
  20 #include "isajet/qcdpar.inc"
  21 #include "isajet/const.inc"
  22 #include "isajet/wcon.inc"
  23 #include "isajet/primar.inc"
  24 C
  25       REAL AM0,AM1,AM2,AMASS,T0,T1,T2,ZC,B0,GAMEW,GAMQQ,GAMGG,GAM,GAMZC
  26       REAL AM1W,AM2W,T1W,T2W,TERM,GB,PROB,RANF,RND,POW,AMNEW,AMOLD
  27       REAL POWEW
  28       INTEGER J,JTLV1,NF,IQ,JTABS,IW,JT0,JT1,IFL1,I
  29       INTEGER JWTYPE(4)
  30       DATA JWTYPE/10,80,-80,90/
  31 C
  32 C          Set ZC = 0 and return for W+- or Z0
  33 C
  34       JTABS=IABS(JTYPE(J))
  35       IF(JTABS.GE.80.AND.JTABS.LE.90) THEN
  36         ZZC(J)=0.
  37         RETURN
  38       ENDIF
  39 C
  40 C          Calculate ZC
  41 C
  42       AM0=PJSET(5,J)
  43       JTLV1=JTYPE(J)
  44       AM1=AMASS(JTLV1)+CUTJET
  45       AM2=CUTJET
  46       IF(AM1+AM2.GE.AM0) GO TO 300
  47       T0=AM0**2
  48       T1=AM1**2
  49       T2=AM2**2
  50       ZC=(T0-T1+T2-SQRT((T0-T1-T2)**2-4*T1*T2))/(2*T0)
  51       ZZC(J)=ZC
  52 C          Count light fermions
  53       NF=3
  54       DO 110 IQ=4,6
  55       IF(AM0.LT.2*AMASS(IQ)) GO TO 120
  56       NF=NF+1
  57 110   CONTINUE
  58 120   B0=11.-2.*NF/3.
  59 C
  60 C          Calculate GAMMA(ZC) and GAMEW for quarks
  61 C
  62       GAMEW=0.
  63 C
  64 C          Initial gluon
  65       IF(JTABS.EQ.9) THEN
  66         GAMQQ=(1.-2.*ZC)*(1.-ZC*(1.-ZC))/3.
  67         GAMGG=12.*ALOG((1.-ZC)/ZC)-9.*(1.-2.*ZC)-6.*GAMQQ
  68         GAMGG=0.5*GAMGG
  69         GAM=GAMGG+NF*GAMQQ
  70 C
  71 C          Initial quark
  72       ELSEIF(JTABS.LT.9) THEN
  73         GAMZC=2.*ALOG((1-ZC)/ZC)-1.5*(1.-2.*ZC)
  74         GAM=4./3.*GAMZC
  75         GAMEW=ALFA/(2.*PI)*AQ(JTABS,1)**2*GAMZC
  76         IF(AM0.GT.WMASS(4)) THEN
  77           DO 130 IW=2,4
  78             JT0=2*IABS(JTYPE(J))
  79             IF(JTYPE(J).LT.0) JT0=JT0+1
  80             JT1=MATCH(JT0,IW)
  81             IF(JT1.EQ.0) GO TO 130
  82             JT1=MATCH(JT1,4)
  83             IFL1=JT1/2
  84             AM1W=AMASS(IFL1)
  85             AM2W=AMASS(JWTYPE(IW))
  86             IF(AM1W+AM2W.GE.AM0) GO TO 130
  87             T1W=AM1W**2
  88             T2W=AM2W**2
  89             ZC=(T0-T1W+T2W-SQRT((T0-T1W-T2W)**2-4*T1W*T2W))/(2*T0)
  90             GAMZC=2.*ALOG((1-ZC)/ZC)-1.5*(1.-2.*ZC)
  91             TERM=(AQ(JTABS,IW)**2+BQ(JTABS,IW)**2)*GAMZC
  92             GAMEW=GAMEW+ALFA/(2.*PI)*TERM
  93 130       CONTINUE
  94         ENDIF
  95 C
  96 C          Initial diquark
  97       ELSEIF(MOD(JTABS,100).EQ.0) THEN
  98         GAM=8./3.*ALOG((1-ZC)/ZC)-2.*(1.-2.*ZC)
  99 C
 100 C          Initial gluino
 101       ELSEIF(JTABS.EQ.29) THEN
 102         GAM=6.*ALOG((1.-ZC)/ZC)-9./2.*(1.-2.*ZC)
 103 C
 104 C          Initial squark
 105       ELSEIF(JTABS.GT.20.AND.JTABS.LT.29) THEN
 106         GAM = 8./3.*(ALOG((1.-ZC)/ZC)-(1.-2.*ZC))
 107       ENDIF
 108 C
 109 C          Generate new mass
 110 C
 111       GB=2*GAM/B0
 112       PROB=(ALOG(AM1/ALAM)/ALOG(AM0/ALAM))**GB
 113       PROB=PROB*(AM1/AM0)**(2.*GAMEW)
 114       IF(PROB.GT.RANF()) GO TO 300
 115       RND=RANF()
 116       POW=(1.-(1.-PROB)*RND)**(1./GB)
 117       AMNEW=ALAM*(AM0/ALAM)**POW
 118 C          For quark, add effect of GM, W+-, Z0 radiation
 119       IF(IABS(JTYPE(J)).LT.9) THEN
 120         DO 200 I=1,NTRIES
 121           AMOLD=AMNEW
 122           POWEW=POW/((AMOLD/AM0)**(2.*GAMEW))**(1./GB)
 123           AMNEW=ALAM*(AM0/ALAM)**POWEW
 124           IF(ABS(AMNEW-AMOLD).LT.0.001*AMOLD) GO TO 210
 125 200    CONTINUE
 126       ENDIF
 127 210   IF(AMNEW.LE.AM1) GO TO 300
 128       PJSET(5,J)=AMNEW
 129       RETURN
 130 C
 131 C          Final parton -- set mass to physical value
 132 C
 133 300   PJSET(5,J)=AM1-CUTJET
 134       JDCAY(J)=0
 135       RETURN
 136       END