PYTHIA/jetset/luonia.F

   1
   2 C*********************************************************************
   3
   4       SUBROUTINE LUONIA(KFL,ECM)
   5
   6 C...Purpose: to generate Upsilon and toponium decays into three
   7 C...gluons or two gluons and a photon.
   8       COMMON/LUJETS/N,K(4000,5),P(4000,5),V(4000,5)
   9       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
  10       COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
  11       SAVE /LUJETS/,/LUDAT1/,/LUDAT2/
  12
  13 C...Printout. Check input parameters.
  14       IF(MSTU(12).GE.1) CALL LULIST(0)
  15       IF(KFL.LT.0.OR.KFL.GT.8) THEN
  16         CALL LUERRM(16,'(LUONIA:) called with unknown flavour code')
  17         IF(MSTU(21).GE.1) RETURN
  18       ENDIF
  19       IF(ECM.LT.PARJ(127)+2.02*PARF(101)) THEN
  20         CALL LUERRM(16,'(LUONIA:) called with too small CM energy')
  21         IF(MSTU(21).GE.1) RETURN
  22       ENDIF
  23
  24 C...Initial e+e- and onium state (optional).
  25       NC=0
  26       IF(MSTJ(115).GE.2) THEN
  27         NC=NC+2
  28         CALL LU1ENT(NC-1,11,0.5*ECM,0.,0.)
  29         K(NC-1,1)=21
  30         CALL LU1ENT(NC,-11,0.5*ECM,PARU(1),0.)
  31         K(NC,1)=21
  32       ENDIF
  33       KFLC=IABS(KFL)
  34       IF(MSTJ(115).GE.3.AND.KFLC.GE.5) THEN
  35         NC=NC+1
  36         KF=110*KFLC+3
  37         MSTU10=MSTU(10)
  38         MSTU(10)=1
  39         P(NC,5)=ECM
  40         CALL LU1ENT(NC,KF,ECM,0.,0.)
  41         K(NC,1)=21
  42         K(NC,3)=1
  43         MSTU(10)=MSTU10
  44       ENDIF
  45
  46 C...Choose x1 and x2 according to matrix element.
  47       NTRY=0
  48   100 X1=RLU(0)
  49       X2=RLU(0)
  50       X3=2.-X1-X2
  51       IF(X3.GE.1..OR.((1.-X1)/(X2*X3))**2+((1.-X2)/(X1*X3))**2+
  52      &((1.-X3)/(X1*X2))**2.LE.2.*RLU(0)) GOTO 100
  53       NTRY=NTRY+1
  54       NJET=3
  55       IF(MSTJ(101).LE.4) CALL LU3ENT(NC+1,21,21,21,ECM,X1,X3)
  56       IF(MSTJ(101).GE.5) CALL LU3ENT(-(NC+1),21,21,21,ECM,X1,X3)
  57
  58 C...Photon-gluon-gluon events. Small system modifications. Jet origin.
  59       MSTU(111)=MSTJ(108)
  60       IF(MSTJ(108).EQ.2.AND.(MSTJ(101).EQ.0.OR.MSTJ(101).EQ.1))
  61      &MSTU(111)=1
  62       PARU(112)=PARJ(121)
  63       IF(MSTU(111).EQ.2) PARU(112)=PARJ(122)
  64       QF=0.
  65       IF(KFLC.NE.0) QF=KCHG(KFLC,1)/3.
  66       RGAM=7.2*QF**2*PARU(101)/ULALPS(ECM**2)
  67       MK=0
  68       ECMC=ECM
  69       IF(RLU(0).GT.RGAM/(1.+RGAM)) THEN
  70         IF(1.-MAX(X1,X2,X3).LE.MAX((PARJ(126)/ECM)**2,PARJ(125)))
  71      &  NJET=2
  72         IF(NJET.EQ.2.AND.MSTJ(101).LE.4) CALL LU2ENT(NC+1,21,21,ECM)
  73         IF(NJET.EQ.2.AND.MSTJ(101).GE.5) CALL LU2ENT(-(NC+1),21,21,ECM)
  74       ELSE
  75         MK=1
  76         ECMC=SQRT(1.-X1)*ECM
  77         IF(ECMC.LT.2.*PARJ(127)) GOTO 100
  78         K(NC+1,1)=1
  79         K(NC+1,2)=22
  80         K(NC+1,4)=0
  81         K(NC+1,5)=0
  82         IF(MSTJ(101).GE.5) K(NC+2,4)=MSTU(5)*(NC+3)
  83         IF(MSTJ(101).GE.5) K(NC+2,5)=MSTU(5)*(NC+3)
  84         IF(MSTJ(101).GE.5) K(NC+3,4)=MSTU(5)*(NC+2)
  85         IF(MSTJ(101).GE.5) K(NC+3,5)=MSTU(5)*(NC+2)
  86         NJET=2
  87         IF(ECMC.LT.4.*PARJ(127)) THEN
  88           MSTU10=MSTU(10)
  89           MSTU(10)=1
  90           P(NC+2,5)=ECMC
  91           CALL LU1ENT(NC+2,83,0.5*(X2+X3)*ECM,PARU(1),0.)
  92           MSTU(10)=MSTU10
  93           NJET=0
  94         ENDIF
  95       ENDIF
  96       DO 110 IP=NC+1,N
  97       K(IP,3)=K(IP,3)+(MSTJ(115)/2)+(KFLC/5)*(MSTJ(115)/3)*(NC-1)
  98   110 CONTINUE
  99
 100 C...Differential cross-sections. Upper limit for cross-section.
 101       IF(MSTJ(106).EQ.1) THEN
 102         SQ2=SQRT(2.)
 103         HF1=1.-PARJ(131)*PARJ(132)
 104         HF3=PARJ(133)**2
 105         CT13=(X1*X3-2.*X1-2.*X3+2.)/(X1*X3)
 106         ST13=SQRT(1.-CT13**2)
 107         SIGL=0.5*X3**2*((1.-X2)**2+(1.-X3)**2)*ST13**2
 108         SIGU=(X1*(1.-X1))**2+(X2*(1.-X2))**2+(X3*(1.-X3))**2-SIGL
 109         SIGT=0.5*SIGL
 110         SIGI=(SIGL*CT13/ST13+0.5*X1*X3*(1.-X2)**2*ST13)/SQ2
 111         SIGMAX=(2.*HF1+HF3)*ABS(SIGU)+2.*(HF1+HF3)*ABS(SIGL)+2.*(HF1+
 112      &  2.*HF3)*ABS(SIGT)+2.*SQ2*(HF1+2.*HF3)*ABS(SIGI)
 113
 114 C...Angular orientation of event.
 115   120   CHI=PARU(2)*RLU(0)
 116         CTHE=2.*RLU(0)-1.
 117         PHI=PARU(2)*RLU(0)
 118         CCHI=COS(CHI)
 119         SCHI=SIN(CHI)
 120         C2CHI=COS(2.*CHI)
 121         S2CHI=SIN(2.*CHI)
 122         THE=ACOS(CTHE)
 123         STHE=SIN(THE)
 124         C2PHI=COS(2.*(PHI-PARJ(134)))
 125         S2PHI=SIN(2.*(PHI-PARJ(134)))
 126         SIG=((1.+CTHE**2)*HF1+STHE**2*C2PHI*HF3)*SIGU+2.*(STHE**2*HF1-
 127      &  STHE**2*C2PHI*HF3)*SIGL+2.*(STHE**2*C2CHI*HF1+((1.+CTHE**2)*
 128      &  C2CHI*C2PHI-2.*CTHE*S2CHI*S2PHI)*HF3)*SIGT-2.*SQ2*(2.*STHE*CTHE*
 129      &  CCHI*HF1-2.*STHE*(CTHE*CCHI*C2PHI-SCHI*S2PHI)*HF3)*SIGI
 130         IF(SIG.LT.SIGMAX*RLU(0)) GOTO 120
 131         CALL LUDBRB(NC+1,N,0.,CHI,0D0,0D0,0D0)
 132         CALL LUDBRB(NC+1,N,THE,PHI,0D0,0D0,0D0)
 133       ENDIF
 134
 135 C...Generate parton shower. Rearrange along strings and check.
 136       IF(MSTJ(101).GE.5.AND.NJET.GE.2) THEN
 137         CALL LUSHOW(NC+MK+1,-NJET,ECMC)
 138         MSTJ14=MSTJ(14)
 139         IF(MSTJ(105).EQ.-1) MSTJ(14)=-1
 140         IF(MSTJ(105).GE.0) MSTU(28)=0
 141         CALL LUPREP(0)
 142         MSTJ(14)=MSTJ14
 143         IF(MSTJ(105).GE.0.AND.MSTU(28).NE.0) GOTO 100
 144       ENDIF
 145
 146 C...Generate fragmentation. Information for LUTABU:
 147       IF(MSTJ(105).EQ.1) CALL LUEXEC
 148       MSTU(161)=110*KFLC+3
 149       MSTU(162)=0
 150
 151       RETURN
 152       END