HIJING/hipyset1_35/luxdif_hijing.F

   1 * $Id$
   2
   3 C*********************************************************************
   4
   5       SUBROUTINE LUXDIF_HIJING(NC,NJET,KFL,ECM,CHI,THE,PHI)
   6
   7 C...Purpose: to give the angular orientation of events.
   8 #include "lujets_hijing.inc"
   9 #include "ludat1_hijing.inc"
  10 #include "ludat2_hijing.inc"
  11
  12 C...Charge. Factors depending on polarization for QED case.
  13       QF=KCHG(KFL,1)/3.
  14       POLL=1.-PARJ(131)*PARJ(132)
  15       POLD=PARJ(132)-PARJ(131)
  16       IF(MSTJ(102).LE.1.OR.MSTJ(109).EQ.1) THEN
  17         HF1=POLL
  18         HF2=0.
  19         HF3=PARJ(133)**2
  20         HF4=0.
  21
  22 C...Factors depending on flavour, energy and polarization for QFD case.
  23       ELSE
  24         SFF=1./(16.*PARU(102)*(1.-PARU(102)))
  25         SFW=ECM**4/((ECM**2-PARJ(123)**2)**2+(PARJ(123)*PARJ(124))**2)
  26         SFI=SFW*(1.-(PARJ(123)/ECM)**2)
  27         AE=-1.
  28         VE=4.*PARU(102)-1.
  29         AF=SIGN(1.,QF)
  30         VF=AF-4.*QF*PARU(102)
  31         HF1=QF**2*POLL-2.*QF*VF*SFI*SFF*(VE*POLL-AE*POLD)+
  32      &  (VF**2+AF**2)*SFW*SFF**2*((VE**2+AE**2)*POLL-2.*VE*AE*POLD)
  33         HF2=-2.*QF*AF*SFI*SFF*(AE*POLL-VE*POLD)+2.*VF*AF*SFW*SFF**2*
  34      &  (2.*VE*AE*POLL-(VE**2+AE**2)*POLD)
  35         HF3=PARJ(133)**2*(QF**2-2.*QF*VF*SFI*SFF*VE+(VF**2+AF**2)*
  36      &  SFW*SFF**2*(VE**2-AE**2))
  37         HF4=-PARJ(133)**2*2.*QF*VF*SFW*(PARJ(123)*PARJ(124)/ECM**2)*
  38      &  SFF*AE
  39       ENDIF
  40
  41 C...Mass factor. Differential cross-sections for two-jet events.
  42       SQ2=SQRT(2.)
  43       QME=0.
  44       IF(MSTJ(103).GE.4.AND.IABS(MSTJ(101)).LE.1.AND.MSTJ(102).LE.1.AND.
  45      &MSTJ(109).NE.1) QME=(2.*ULMASS_HIJING(KFL)/ECM)**2
  46       IF(NJET.EQ.2) THEN
  47         SIGU=4.*SQRT(1.-QME)
  48         SIGL=2.*QME*SQRT(1.-QME)
  49         SIGT=0.
  50         SIGI=0.
  51         SIGA=0.
  52         SIGP=4.
  53
  54 C...Kinematical variables. Reduce four-jet event to three-jet one.
  55       ELSE
  56         IF(NJET.EQ.3) THEN
  57           X1=2.*P(NC+1,4)/ECM
  58           X2=2.*P(NC+3,4)/ECM
  59         ELSE
  60           ECMR=P(NC+1,4)+P(NC+4,4)+SQRT((P(NC+2,1)+P(NC+3,1))**2+
  61      &    (P(NC+2,2)+P(NC+3,2))**2+(P(NC+2,3)+P(NC+3,3))**2)
  62           X1=2.*P(NC+1,4)/ECMR
  63           X2=2.*P(NC+4,4)/ECMR
  64         ENDIF
  65
  66 C...Differential cross-sections for three-jet (or reduced four-jet).
  67         XQ=(1.-X1)/(1.-X2)
  68         CT12=(X1*X2-2.*X1-2.*X2+2.+QME)/SQRT((X1**2-QME)*(X2**2-QME))
  69         ST12=SQRT(1.-CT12**2)
  70         IF(MSTJ(109).NE.1) THEN
  71           SIGU=2.*X1**2+X2**2*(1.+CT12**2)-QME*(3.+CT12**2-X1-X2)-
  72      &    QME*X1/XQ+0.5*QME*((X2**2-QME)*ST12**2-2.*X2)*XQ
  73           SIGL=(X2*ST12)**2-QME*(3.-CT12**2-2.5*(X1+X2)+X1*X2+QME)+
  74      &    0.5*QME*(X1**2-X1-QME)/XQ+0.5*QME*((X2**2-QME)*CT12**2-X2)*XQ
  75           SIGT=0.5*(X2**2-QME-0.5*QME*(X2**2-QME)/XQ)*ST12**2
  76           SIGI=((1.-0.5*QME*XQ)*(X2**2-QME)*ST12*CT12+QME*(1.-X1-X2+
  77      &    0.5*X1*X2+0.5*QME)*ST12/CT12)/SQ2
  78           SIGA=X2**2*ST12/SQ2
  79           SIGP=2.*(X1**2-X2**2*CT12)
  80
  81 C...Differential cross-sect for scalar gluons (no mass or QFD effects).
  82         ELSE
  83           SIGU=2.*(2.-X1-X2)**2-(X2*ST12)**2
  84           SIGL=(X2*ST12)**2
  85           SIGT=0.5*SIGL
  86           SIGI=-(2.-X1-X2)*X2*ST12/SQ2
  87           SIGA=0.
  88           SIGP=0.
  89         ENDIF
  90       ENDIF
  91
  92 C...Upper bounds for differential cross-section.
  93       HF1A=ABS(HF1)
  94       HF2A=ABS(HF2)
  95       HF3A=ABS(HF3)
  96       HF4A=ABS(HF4)
  97       SIGMAX=(2.*HF1A+HF3A+HF4A)*ABS(SIGU)+2.*(HF1A+HF3A+HF4A)*
  98      &ABS(SIGL)+2.*(HF1A+2.*HF3A+2.*HF4A)*ABS(SIGT)+2.*SQ2*
  99      &(HF1A+2.*HF3A+2.*HF4A)*ABS(SIGI)+4.*SQ2*HF2A*ABS(SIGA)+
 100      &2.*HF2A*ABS(SIGP)
 101
 102 C...Generate angular orientation according to differential cross-sect.
 103   100 CHI=PARU(2)*RLU_HIJING(0)
 104       CTHE=2.*RLU_HIJING(0)-1.
 105       PHI=PARU(2)*RLU_HIJING(0)
 106       CCHI=COS(CHI)
 107       SCHI=SIN(CHI)
 108       C2CHI=COS(2.*CHI)
 109       S2CHI=SIN(2.*CHI)
 110       THE=ACOS(CTHE)
 111       STHE=SIN(THE)
 112       C2PHI=COS(2.*(PHI-PARJ(134)))
 113       S2PHI=SIN(2.*(PHI-PARJ(134)))
 114       SIG=((1.+CTHE**2)*HF1+STHE**2*(C2PHI*HF3-S2PHI*HF4))*SIGU+
 115      &2.*(STHE**2*HF1-STHE**2*(C2PHI*HF3-S2PHI*HF4))*SIGL+
 116      &2.*(STHE**2*C2CHI*HF1+((1.+CTHE**2)*C2CHI*C2PHI-2.*CTHE*S2CHI*
 117      &S2PHI)*HF3-((1.+CTHE**2)*C2CHI*S2PHI+2.*CTHE*S2CHI*C2PHI)*HF4)*
 118      &SIGT-2.*SQ2*(2.*STHE*CTHE*CCHI*HF1-2.*STHE*(CTHE*CCHI*C2PHI-
 119      &SCHI*S2PHI)*HF3+2.*STHE*(CTHE*CCHI*S2PHI+SCHI*C2PHI)*HF4)*SIGI+
 120      &4.*SQ2*STHE*CCHI*HF2*SIGA+2.*CTHE*HF2*SIGP
 121       IF(SIG.LT.SIGMAX*RLU_HIJING(0)) GOTO 100
 122
 123       RETURN
 124       END