hijing/src/lueevt.f

0001
0002 C*********************************************************************
0003
0004       SUBROUTINE LUEEVT(KFL,ECM)
0005
0006 C...Purpose: to handle the generation of an e+e- annihilation jet event.
0007       IMPLICIT DOUBLE PRECISION(D)
0008       COMMON/LUJETS/N,K(9000,5),P(9000,5),V(9000,5)
0009       SAVE /LUJETS/
0010       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
0011       SAVE /LUDAT1/
0012       COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
0013       SAVE /LUDAT2/
0014
0015 C...Check input parameters.
0016       IF(MSTU(12).GE.1) CALL LULIST(0)
0017       IF(KFL.LT.0.OR.KFL.GT.8) THEN
0018         CALL LUERRM(16,'(LUEEVT:) called with unknown flavour code')
0019         IF(MSTU(21).GE.1) RETURN
0020       ENDIF
0021       IF(KFL.LE.5) ECMMIN=PARJ(127)+2.02*PARF(100+MAX(1,KFL))
0022       IF(KFL.GE.6) ECMMIN=PARJ(127)+2.02*PMAS(KFL,1)
0023       IF(ECM.LT.ECMMIN) THEN
0024         CALL LUERRM(16,'(LUEEVT:) called with too small CM energy')
0025         IF(MSTU(21).GE.1) RETURN
0026       ENDIF
0027
0028 C...Check consistency of MSTJ options set.
0029       IF(MSTJ(109).EQ.2.AND.MSTJ(110).NE.1) THEN
0030         CALL LUERRM(6,
0031      &  '(LUEEVT:) MSTJ(109) value requires MSTJ(110) = 1')
0032         MSTJ(110)=1
0033       ENDIF
0034       IF(MSTJ(109).EQ.2.AND.MSTJ(111).NE.0) THEN
0035         CALL LUERRM(6,
0036      &  '(LUEEVT:) MSTJ(109) value requires MSTJ(111) = 0')
0037         MSTJ(111)=0
0038       ENDIF
0039
0040 C...Initialize alpha_strong and total cross-section.
0041       MSTU(111)=MSTJ(108)
0042       IF(MSTJ(108).EQ.2.AND.(MSTJ(101).EQ.0.OR.MSTJ(101).EQ.1))
0043      &MSTU(111)=1
0044       PARU(112)=PARJ(121)
0045       IF(MSTU(111).EQ.2) PARU(112)=PARJ(122)
0046       IF(MSTJ(116).GT.0.AND.(MSTJ(116).GE.2.OR.ABS(ECM-PARJ(151)).GE.
0047      &PARJ(139).OR.10*MSTJ(102)+KFL.NE.MSTJ(119))) CALL LUXTOT(KFL,ECM,
0048      &XTOT)
0049       IF(MSTJ(116).GE.3) MSTJ(116)=1
0050
0051 C...Add initial e+e- to event record (documentation only).
0052       NTRY=0
0053   100 NTRY=NTRY+1
0054       IF(NTRY.GT.100) THEN
0055         CALL LUERRM(14,'(LUEEVT:) caught in an infinite loop')
0056         RETURN
0057       ENDIF
0058       NC=0
0059       IF(MSTJ(115).GE.2) THEN
0060         NC=NC+2
0061         CALL LU1ENT(NC-1,11,0.5*ECM,0.,0.)
0062         K(NC-1,1)=21
0063         CALL LU1ENT(NC,-11,0.5*ECM,PARU(1),0.)
0064         K(NC,1)=21
0065       ENDIF
0066
0067 C...Radiative photon (in initial state).
0068       MK=0
0069       ECMC=ECM
0070       IF(MSTJ(107).GE.1.AND.MSTJ(116).GE.1) CALL LURADK(ECM,MK,PAK,
0071      &THEK,PHIK,ALPK)
0072       IF(MK.EQ.1) ECMC=SQRT(ECM*(ECM-2.*PAK))
0073       IF(MSTJ(115).GE.1.AND.MK.EQ.1) THEN
0074         NC=NC+1
0075         CALL LU1ENT(NC,22,PAK,THEK,PHIK)
0076         K(NC,3)=MIN(MSTJ(115)/2,1)
0077       ENDIF
0078
0079 C...Virtual exchange boson (gamma or Z0).
0080       IF(MSTJ(115).GE.3) THEN
0081         NC=NC+1
0082         KF=22
0083         IF(MSTJ(102).EQ.2) KF=23
0084         MSTU10=MSTU(10)
0085         MSTU(10)=1
0086         P(NC,5)=ECMC
0087         CALL LU1ENT(NC,KF,ECMC,0.,0.)
0088         K(NC,1)=21
0089         K(NC,3)=1
0090         MSTU(10)=MSTU10
0091       ENDIF
0092
0093 C...Choice of flavour and jet configuration.
0094       CALL LUXKFL(KFL,ECM,ECMC,KFLC)
0095       IF(KFLC.EQ.0) GOTO 100
0096       CALL LUXJET(ECMC,NJET,CUT)
0097       KFLN=21
0098       IF(NJET.EQ.4) CALL LUX4JT(NJET,CUT,KFLC,ECMC,KFLN,X1,X2,X4,
0099      &X12,X14)
0100       IF(NJET.EQ.3) CALL LUX3JT(NJET,CUT,KFLC,ECMC,X1,X3)
0101       IF(NJET.EQ.2) MSTJ(120)=1
0102
0103 C...Fill jet configuration and origin.
0104       IF(NJET.EQ.2.AND.MSTJ(101).NE.5) CALL LU2ENT(NC+1,KFLC,-KFLC,ECMC)
0105       IF(NJET.EQ.2.AND.MSTJ(101).EQ.5) CALL LU2ENT(-(NC+1),KFLC,-KFLC,
0106      &ECMC)
0107       IF(NJET.EQ.3) CALL LU3ENT(NC+1,KFLC,21,-KFLC,ECMC,X1,X3)
0108       IF(NJET.EQ.4.AND.KFLN.EQ.21) CALL LU4ENT(NC+1,KFLC,KFLN,KFLN,
0109      &-KFLC,ECMC,X1,X2,X4,X12,X14)
0110       IF(NJET.EQ.4.AND.KFLN.NE.21) CALL LU4ENT(NC+1,KFLC,-KFLN,KFLN,
0111      &-KFLC,ECMC,X1,X2,X4,X12,X14)
0112       DO 110 IP=NC+1,N
0113   110 K(IP,3)=K(IP,3)+MIN(MSTJ(115)/2,1)+(MSTJ(115)/3)*(NC-1)
0114
0115 C...Angular orientation according to matrix element.
0116       IF(MSTJ(106).EQ.1) THEN
0117         CALL LUXDIF(NC,NJET,KFLC,ECMC,CHI,THE,PHI)
0118         CALL LUDBRB(NC+1,N,0.,CHI,0D0,0D0,0D0)
0119         CALL LUDBRB(NC+1,N,THE,PHI,0D0,0D0,0D0)
0120       ENDIF
0121
0122 C...Rotation and boost from radiative photon.
0123       IF(MK.EQ.1) THEN
0124         DBEK=-PAK/(ECM-PAK)
0125         NMIN=NC+1-MSTJ(115)/3
0126         CALL LUDBRB(NMIN,N,0.,-PHIK,0D0,0D0,0D0)
0127         CALL LUDBRB(NMIN,N,ALPK,0.,DBEK*SIN(THEK),0D0,DBEK*COS(THEK))
0128         CALL LUDBRB(NMIN,N,0.,PHIK,0D0,0D0,0D0)
0129       ENDIF
0130
0131 C...Generate parton shower. Rearrange along strings and check.
0132       IF(MSTJ(101).EQ.5) THEN
0133         CALL LUSHOW(N-1,N,ECMC)
0134         MSTJ14=MSTJ(14)
0135         IF(MSTJ(105).EQ.-1) MSTJ(14)=0
0136         IF(MSTJ(105).GE.0) MSTU(28)=0
0137         CALL LUPREP(0)
0138         MSTJ(14)=MSTJ14
0139         IF(MSTJ(105).GE.0.AND.MSTU(28).NE.0) GOTO 100
0140       ENDIF
0141
0142 C...Fragmentation/decay generation. Information for LUTABU.
0143       IF(MSTJ(105).EQ.1) CALL LUEXEC
0144       MSTU(161)=KFLC
0145       MSTU(162)=-KFLC
0146
0147       RETURN
0148       END