PYTHIA/jetset/lueevt.F

   1
   2 C*********************************************************************
   3
   4       SUBROUTINE LUEEVT(KFL,ECM)
   5
   6 C...Purpose: to handle the generation of an e+e- annihilation jet event.
   7       IMPLICIT DOUBLE PRECISION(D)
   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...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,'(LUEEVT:) called with unknown flavour code')
  17         IF(MSTU(21).GE.1) RETURN
  18       ENDIF
  19       IF(KFL.LE.5) ECMMIN=PARJ(127)+2.02*PARF(100+MAX(1,KFL))
  20       IF(KFL.GE.6) ECMMIN=PARJ(127)+2.02*PMAS(KFL,1)
  21       IF(ECM.LT.ECMMIN) THEN
  22         CALL LUERRM(16,'(LUEEVT:) called with too small CM energy')
  23         IF(MSTU(21).GE.1) RETURN
  24       ENDIF
  25
  26 C...Check consistency of MSTJ options set.
  27       IF(MSTJ(109).EQ.2.AND.MSTJ(110).NE.1) THEN
  28         CALL LUERRM(6,
  29      &  '(LUEEVT:) MSTJ(109) value requires MSTJ(110) = 1')
  30         MSTJ(110)=1
  31       ENDIF
  32       IF(MSTJ(109).EQ.2.AND.MSTJ(111).NE.0) THEN
  33         CALL LUERRM(6,
  34      &  '(LUEEVT:) MSTJ(109) value requires MSTJ(111) = 0')
  35         MSTJ(111)=0
  36       ENDIF
  37
  38 C...Initialize alpha_strong and total cross-section.
  39       MSTU(111)=MSTJ(108)
  40       IF(MSTJ(108).EQ.2.AND.(MSTJ(101).EQ.0.OR.MSTJ(101).EQ.1))
  41      &MSTU(111)=1
  42       PARU(112)=PARJ(121)
  43       IF(MSTU(111).EQ.2) PARU(112)=PARJ(122)
  44       IF(MSTJ(116).GT.0.AND.(MSTJ(116).GE.2.OR.ABS(ECM-PARJ(151)).GE.
  45      &PARJ(139).OR.10*MSTJ(102)+KFL.NE.MSTJ(119))) CALL LUXTOT(KFL,ECM,
  46      &XTOT)
  47       IF(MSTJ(116).GE.3) MSTJ(116)=1
  48       PARJ(171)=0.
  49
  50 C...Add initial e+e- to event record (documentation only).
  51       NTRY=0
  52   100 NTRY=NTRY+1
  53       IF(NTRY.GT.100) THEN
  54         CALL LUERRM(14,'(LUEEVT:) caught in an infinite loop')
  55         RETURN
  56       ENDIF
  57       MSTU(24)=0
  58       NC=0
  59       IF(MSTJ(115).GE.2) THEN
  60         NC=NC+2
  61         CALL LU1ENT(NC-1,11,0.5*ECM,0.,0.)
  62         K(NC-1,1)=21
  63         CALL LU1ENT(NC,-11,0.5*ECM,PARU(1),0.)
  64         K(NC,1)=21
  65       ENDIF
  66
  67 C...Radiative photon (in initial state).
  68       MK=0
  69       ECMC=ECM
  70       IF(MSTJ(107).GE.1.AND.MSTJ(116).GE.1) CALL LURADK(ECM,MK,PAK,
  71      &THEK,PHIK,ALPK)
  72       IF(MK.EQ.1) ECMC=SQRT(ECM*(ECM-2.*PAK))
  73       IF(MSTJ(115).GE.1.AND.MK.EQ.1) THEN
  74         NC=NC+1
  75         CALL LU1ENT(NC,22,PAK,THEK,PHIK)
  76         K(NC,3)=MIN(MSTJ(115)/2,1)
  77       ENDIF
  78
  79 C...Virtual exchange boson (gamma or Z0).
  80       IF(MSTJ(115).GE.3) THEN
  81         NC=NC+1
  82         KF=22
  83         IF(MSTJ(102).EQ.2) KF=23
  84         MSTU10=MSTU(10)
  85         MSTU(10)=1
  86         P(NC,5)=ECMC
  87         CALL LU1ENT(NC,KF,ECMC,0.,0.)
  88         K(NC,1)=21
  89         K(NC,3)=1
  90         MSTU(10)=MSTU10
  91       ENDIF
  92
  93 C...Choice of flavour and jet configuration.
  94       CALL LUXKFL(KFL,ECM,ECMC,KFLC)
  95       IF(KFLC.EQ.0) GOTO 100
  96       CALL LUXJET(ECMC,NJET,CUT)
  97       KFLN=21
  98       IF(NJET.EQ.4) CALL LUX4JT(NJET,CUT,KFLC,ECMC,KFLN,X1,X2,X4,
  99      &X12,X14)
 100       IF(NJET.EQ.3) CALL LUX3JT(NJET,CUT,KFLC,ECMC,X1,X3)
 101       IF(NJET.EQ.2) MSTJ(120)=1
 102
 103 C...Fill jet configuration and origin.
 104       IF(NJET.EQ.2.AND.MSTJ(101).NE.5) CALL LU2ENT(NC+1,KFLC,-KFLC,ECMC)
 105       IF(NJET.EQ.2.AND.MSTJ(101).EQ.5) CALL LU2ENT(-(NC+1),KFLC,-KFLC,
 106      &ECMC)
 107       IF(NJET.EQ.3) CALL LU3ENT(NC+1,KFLC,21,-KFLC,ECMC,X1,X3)
 108       IF(NJET.EQ.4.AND.KFLN.EQ.21) CALL LU4ENT(NC+1,KFLC,KFLN,KFLN,
 109      &-KFLC,ECMC,X1,X2,X4,X12,X14)
 110       IF(NJET.EQ.4.AND.KFLN.NE.21) CALL LU4ENT(NC+1,KFLC,-KFLN,KFLN,
 111      &-KFLC,ECMC,X1,X2,X4,X12,X14)
 112       IF(MSTU(24).NE.0) GOTO 100
 113       DO 110 IP=NC+1,N
 114       K(IP,3)=K(IP,3)+MIN(MSTJ(115)/2,1)+(MSTJ(115)/3)*(NC-1)
 115   110 CONTINUE
 116
 117 C...Angular orientation according to matrix element.
 118       IF(MSTJ(106).EQ.1) THEN
 119         CALL LUXDIF(NC,NJET,KFLC,ECMC,CHI,THE,PHI)
 120         CALL LUDBRB(NC+1,N,0.,CHI,0D0,0D0,0D0)
 121         CALL LUDBRB(NC+1,N,THE,PHI,0D0,0D0,0D0)
 122       ENDIF
 123
 124 C...Rotation and boost from radiative photon.
 125       IF(MK.EQ.1) THEN
 126         DBEK=-PAK/(ECM-PAK)
 127         NMIN=NC+1-MSTJ(115)/3
 128         CALL LUDBRB(NMIN,N,0.,-PHIK,0D0,0D0,0D0)
 129         CALL LUDBRB(NMIN,N,ALPK,0.,DBEK*SIN(THEK),0D0,DBEK*COS(THEK))
 130         CALL LUDBRB(NMIN,N,0.,PHIK,0D0,0D0,0D0)
 131       ENDIF
 132
 133 C...Generate parton shower. Rearrange along strings and check.
 134       IF(MSTJ(101).EQ.5) THEN
 135         CALL LUSHOW(N-1,N,ECMC)
 136         MSTJ14=MSTJ(14)
 137         IF(MSTJ(105).EQ.-1) MSTJ(14)=-1
 138         IF(MSTJ(105).GE.0) MSTU(28)=0
 139         CALL LUPREP(0)
 140         MSTJ(14)=MSTJ14
 141         IF(MSTJ(105).GE.0.AND.MSTU(28).NE.0) GOTO 100
 142       ENDIF
 143
 144 C...Fragmentation/decay generation. Information for LUTABU.
 145       IF(MSTJ(105).EQ.1) CALL LUEXEC
 146       MSTU(161)=KFLC
 147       MSTU(162)=-KFLC
 148
 149       RETURN
 150       END