HIJING/hipyset1_35/luonia_hijing.F

   1 * $Id$
   2
   3 C*********************************************************************
   4
   5       SUBROUTINE LUONIA_HIJING(KFL,ECM)
   6
   7 C...Purpose: to generate Upsilon and toponium decays into three
   8 C...gluons or two gluons and a photon.
   9 #include "lujets_hijing.inc"
  10 #include "ludat1_hijing.inc"
  11 #include "ludat2_hijing.inc"
  12
  13 C...Printout. Check input parameters.
  14       IF(MSTU(12).GE.1) CALL LULIST_HIJING(0)
  15       IF(KFL.LT.0.OR.KFL.GT.8) THEN
  16          CALL LUERRM_HIJING(16
  17      $        ,'(LUONIA_HIJING:) called with unknown flavour code')
  18         IF(MSTU(21).GE.1) RETURN
  19       ENDIF
  20       IF(ECM.LT.PARJ(127)+2.02*PARF(101)) THEN
  21          CALL LUERRM_HIJING(16
  22      $        ,'(LUONIA_HIJING:) called with too small CM energy')
  23         IF(MSTU(21).GE.1) RETURN
  24       ENDIF
  25
  26 C...Initial e+e- and onium state (optional).
  27       NC=0
  28       IF(MSTJ(115).GE.2) THEN
  29         NC=NC+2
  30         CALL LU1ENT_HIJING(NC-1,11,0.5*ECM,0.,0.)
  31         K(NC-1,1)=21
  32         CALL LU1ENT_HIJING(NC,-11,0.5*ECM,PARU(1),0.)
  33         K(NC,1)=21
  34       ENDIF
  35       KFLC=IABS(KFL)
  36       IF(MSTJ(115).GE.3.AND.KFLC.GE.5) THEN
  37         NC=NC+1
  38         KF=110*KFLC+3
  39         MSTU10=MSTU(10)
  40         MSTU(10)=1
  41         P(NC,5)=ECM
  42         CALL LU1ENT_HIJING(NC,KF,ECM,0.,0.)
  43         K(NC,1)=21
  44         K(NC,3)=1
  45         MSTU(10)=MSTU10
  46       ENDIF
  47
  48 C...Choose x1 and x2 according to matrix element.
  49       NTRY=0
  50   100 X1=RLU_HIJING(0)
  51       X2=RLU_HIJING(0)
  52       X3=2.-X1-X2
  53       IF(X3.GE.1..OR.((1.-X1)/(X2*X3))**2+((1.-X2)/(X1*X3))**2+
  54      &((1.-X3)/(X1*X2))**2.LE.2.*RLU_HIJING(0)) GOTO 100
  55       NTRY=NTRY+1
  56       NJET=3
  57       IF(MSTJ(101).LE.4) CALL LU3ENT_HIJING(NC+1,21,21,21,ECM,X1,X3)
  58       IF(MSTJ(101).GE.5) CALL LU3ENT_HIJING(-(NC+1),21,21,21,ECM,X1,X3)
  59
  60 C...Photon-gluon-gluon events. Small system modifications. Jet origin.
  61       MSTU(111)=MSTJ(108)
  62       IF(MSTJ(108).EQ.2.AND.(MSTJ(101).EQ.0.OR.MSTJ(101).EQ.1))
  63      &MSTU(111)=1
  64       PARU(112)=PARJ(121)
  65       IF(MSTU(111).EQ.2) PARU(112)=PARJ(122)
  66       QF=0.
  67       IF(KFLC.NE.0) QF=KCHG(KFLC,1)/3.
  68       RGAM=7.2*QF**2*PARU(101)/ULALPS_HIJING(ECM**2)
  69       MK=0
  70       ECMC=ECM
  71       IF(RLU_HIJING(0).GT.RGAM/(1.+RGAM)) THEN
  72         IF(1.-MAX(X1,X2,X3).LE.MAX((PARJ(126)/ECM)**2,PARJ(125)))
  73      &  NJET=2
  74         IF(NJET.EQ.2.AND.MSTJ(101).LE.4) CALL LU2ENT_HIJING(NC+1,21,21
  75      $       ,ECM)
  76         IF(NJET.EQ.2.AND.MSTJ(101).GE.5) CALL LU2ENT_HIJING(-(NC+1),21
  77      $       ,21,ECM)
  78       ELSE
  79         MK=1
  80         ECMC=SQRT(1.-X1)*ECM
  81         IF(ECMC.LT.2.*PARJ(127)) GOTO 100
  82         K(NC+1,1)=1
  83         K(NC+1,2)=22
  84         K(NC+1,4)=0
  85         K(NC+1,5)=0
  86         IF(MSTJ(101).GE.5) K(NC+2,4)=MSTU(5)*(NC+3)
  87         IF(MSTJ(101).GE.5) K(NC+2,5)=MSTU(5)*(NC+3)
  88         IF(MSTJ(101).GE.5) K(NC+3,4)=MSTU(5)*(NC+2)
  89         IF(MSTJ(101).GE.5) K(NC+3,5)=MSTU(5)*(NC+2)
  90         NJET=2
  91         IF(ECMC.LT.4.*PARJ(127)) THEN
  92           MSTU10=MSTU(10)
  93           MSTU(10)=1
  94           P(NC+2,5)=ECMC
  95           CALL LU1ENT_HIJING(NC+2,83,0.5*(X2+X3)*ECM,PARU(1),0.)
  96           MSTU(10)=MSTU10
  97           NJET=0
  98         ENDIF
  99       ENDIF
 100       DO 110 IP=NC+1,N
 101   110 K(IP,3)=K(IP,3)+(MSTJ(115)/2)+(KFLC/5)*(MSTJ(115)/3)*(NC-1)
 102
 103 C...Differential cross-sections. Upper limit for cross-section.
 104       IF(MSTJ(106).EQ.1) THEN
 105         SQ2=SQRT(2.)
 106         HF1=1.-PARJ(131)*PARJ(132)
 107         HF3=PARJ(133)**2
 108         CT13=(X1*X3-2.*X1-2.*X3+2.)/(X1*X3)
 109         ST13=SQRT(1.-CT13**2)
 110         SIGL=0.5*X3**2*((1.-X2)**2+(1.-X3)**2)*ST13**2
 111         SIGU=(X1*(1.-X1))**2+(X2*(1.-X2))**2+(X3*(1.-X3))**2-SIGL
 112         SIGT=0.5*SIGL
 113         SIGI=(SIGL*CT13/ST13+0.5*X1*X3*(1.-X2)**2*ST13)/SQ2
 114         SIGMAX=(2.*HF1+HF3)*ABS(SIGU)+2.*(HF1+HF3)*ABS(SIGL)+2.*(HF1+
 115      &  2.*HF3)*ABS(SIGT)+2.*SQ2*(HF1+2.*HF3)*ABS(SIGI)
 116
 117 C...Angular orientation of event.
 118   120   CHI=PARU(2)*RLU_HIJING(0)
 119         CTHE=2.*RLU_HIJING(0)-1.
 120         PHI=PARU(2)*RLU_HIJING(0)
 121         CCHI=COS(CHI)
 122         SCHI=SIN(CHI)
 123         C2CHI=COS(2.*CHI)
 124         S2CHI=SIN(2.*CHI)
 125         THE=ACOS(CTHE)
 126         STHE=SIN(THE)
 127         C2PHI=COS(2.*(PHI-PARJ(134)))
 128         S2PHI=SIN(2.*(PHI-PARJ(134)))
 129         SIG=((1.+CTHE**2)*HF1+STHE**2*C2PHI*HF3)*SIGU+2.*(STHE**2*HF1-
 130      &  STHE**2*C2PHI*HF3)*SIGL+2.*(STHE**2*C2CHI*HF1+((1.+CTHE**2)*
 131      &  C2CHI*C2PHI-2.*CTHE*S2CHI*S2PHI)*HF3)*SIGT-2.*SQ2*(2.*STHE*CTHE*
 132      &  CCHI*HF1-2.*STHE*(CTHE*CCHI*C2PHI-SCHI*S2PHI)*HF3)*SIGI
 133         IF(SIG.LT.SIGMAX*RLU_HIJING(0)) GOTO 120
 134         CALL LUDBRB_HIJING(NC+1,N,0.,CHI,0D0,0D0,0D0)
 135         CALL LUDBRB_HIJING(NC+1,N,THE,PHI,0D0,0D0,0D0)
 136       ENDIF
 137
 138 C...Generate parton shower. Rearrange along strings and check.
 139       IF(MSTJ(101).GE.5.AND.NJET.GE.2) THEN
 140         CALL LUSHOW_HIJING(NC+MK+1,-NJET,ECMC)
 141         MSTJ14=MSTJ(14)
 142         IF(MSTJ(105).EQ.-1) MSTJ(14)=0
 143         IF(MSTJ(105).GE.0) MSTU(28)=0
 144         CALL LUPREP_HIJING(0)
 145         MSTJ(14)=MSTJ14
 146         IF(MSTJ(105).GE.0.AND.MSTU(28).NE.0) GOTO 100
 147       ENDIF
 148
 149 C...Generate fragmentation. Information for LUTABU_HIJING:
 150       IF(MSTJ(105).EQ.1) CALL LUEXEC_HIJING
 151       MSTU(161)=110*KFLC+3
 152       MSTU(162)=0
 153
 154       RETURN
 155       END