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[u/mrichter/AliRoot.git] / PYTHIA / jetset / lueevt.F

 
C********************************************************************* 
 
      SUBROUTINE LUEEVT(KFL,ECM) 
 
C...Purpose: to handle the generation of an e+e- annihilation jet event. 
      IMPLICIT DOUBLE PRECISION(D) 
      COMMON/LUJETS/N,K(4000,5),P(4000,5),V(4000,5) 
      COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200) 
      COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4) 
      SAVE /LUJETS/,/LUDAT1/,/LUDAT2/ 
 
C...Check input parameters. 
      IF(MSTU(12).GE.1) CALL LULIST(0) 
      IF(KFL.LT.0.OR.KFL.GT.8) THEN 
        CALL LUERRM(16,'(LUEEVT:) called with unknown flavour code') 
        IF(MSTU(21).GE.1) RETURN 
      ENDIF 
      IF(KFL.LE.5) ECMMIN=PARJ(127)+2.02*PARF(100+MAX(1,KFL)) 
      IF(KFL.GE.6) ECMMIN=PARJ(127)+2.02*PMAS(KFL,1) 
      IF(ECM.LT.ECMMIN) THEN 
        CALL LUERRM(16,'(LUEEVT:) called with too small CM energy') 
        IF(MSTU(21).GE.1) RETURN 
      ENDIF 
 
C...Check consistency of MSTJ options set. 
      IF(MSTJ(109).EQ.2.AND.MSTJ(110).NE.1) THEN 
        CALL LUERRM(6, 
     &  '(LUEEVT:) MSTJ(109) value requires MSTJ(110) = 1') 
        MSTJ(110)=1 
      ENDIF 
      IF(MSTJ(109).EQ.2.AND.MSTJ(111).NE.0) THEN 
        CALL LUERRM(6, 
     &  '(LUEEVT:) MSTJ(109) value requires MSTJ(111) = 0') 
        MSTJ(111)=0 
      ENDIF 
 
C...Initialize alpha_strong and total cross-section. 
      MSTU(111)=MSTJ(108) 
      IF(MSTJ(108).EQ.2.AND.(MSTJ(101).EQ.0.OR.MSTJ(101).EQ.1)) 
     &MSTU(111)=1 
      PARU(112)=PARJ(121) 
      IF(MSTU(111).EQ.2) PARU(112)=PARJ(122) 
      IF(MSTJ(116).GT.0.AND.(MSTJ(116).GE.2.OR.ABS(ECM-PARJ(151)).GE. 
     &PARJ(139).OR.10*MSTJ(102)+KFL.NE.MSTJ(119))) CALL LUXTOT(KFL,ECM, 
     &XTOT) 
      IF(MSTJ(116).GE.3) MSTJ(116)=1 
      PARJ(171)=0. 
 
C...Add initial e+e- to event record (documentation only). 
      NTRY=0 
  100 NTRY=NTRY+1 
      IF(NTRY.GT.100) THEN 
        CALL LUERRM(14,'(LUEEVT:) caught in an infinite loop') 
        RETURN 
      ENDIF 
      MSTU(24)=0 
      NC=0 
      IF(MSTJ(115).GE.2) THEN 
        NC=NC+2 
        CALL LU1ENT(NC-1,11,0.5*ECM,0.,0.) 
        K(NC-1,1)=21 
        CALL LU1ENT(NC,-11,0.5*ECM,PARU(1),0.) 
        K(NC,1)=21 
      ENDIF 
 
C...Radiative photon (in initial state). 
      MK=0 
      ECMC=ECM 
      IF(MSTJ(107).GE.1.AND.MSTJ(116).GE.1) CALL LURADK(ECM,MK,PAK, 
     &THEK,PHIK,ALPK) 
      IF(MK.EQ.1) ECMC=SQRT(ECM*(ECM-2.*PAK)) 
      IF(MSTJ(115).GE.1.AND.MK.EQ.1) THEN 
        NC=NC+1 
        CALL LU1ENT(NC,22,PAK,THEK,PHIK) 
        K(NC,3)=MIN(MSTJ(115)/2,1) 
      ENDIF 
 
C...Virtual exchange boson (gamma or Z0). 
      IF(MSTJ(115).GE.3) THEN 
        NC=NC+1 
        KF=22 
        IF(MSTJ(102).EQ.2) KF=23 
        MSTU10=MSTU(10) 
        MSTU(10)=1 
        P(NC,5)=ECMC 
        CALL LU1ENT(NC,KF,ECMC,0.,0.) 
        K(NC,1)=21 
        K(NC,3)=1 
        MSTU(10)=MSTU10 
      ENDIF 
 
C...Choice of flavour and jet configuration. 
      CALL LUXKFL(KFL,ECM,ECMC,KFLC) 
      IF(KFLC.EQ.0) GOTO 100 
      CALL LUXJET(ECMC,NJET,CUT) 
      KFLN=21 
      IF(NJET.EQ.4) CALL LUX4JT(NJET,CUT,KFLC,ECMC,KFLN,X1,X2,X4, 
     &X12,X14) 
      IF(NJET.EQ.3) CALL LUX3JT(NJET,CUT,KFLC,ECMC,X1,X3) 
      IF(NJET.EQ.2) MSTJ(120)=1 
 
C...Fill jet configuration and origin. 
      IF(NJET.EQ.2.AND.MSTJ(101).NE.5) CALL LU2ENT(NC+1,KFLC,-KFLC,ECMC) 
      IF(NJET.EQ.2.AND.MSTJ(101).EQ.5) CALL LU2ENT(-(NC+1),KFLC,-KFLC, 
     &ECMC) 
      IF(NJET.EQ.3) CALL LU3ENT(NC+1,KFLC,21,-KFLC,ECMC,X1,X3) 
      IF(NJET.EQ.4.AND.KFLN.EQ.21) CALL LU4ENT(NC+1,KFLC,KFLN,KFLN, 
     &-KFLC,ECMC,X1,X2,X4,X12,X14) 
      IF(NJET.EQ.4.AND.KFLN.NE.21) CALL LU4ENT(NC+1,KFLC,-KFLN,KFLN, 
     &-KFLC,ECMC,X1,X2,X4,X12,X14) 
      IF(MSTU(24).NE.0) GOTO 100 
      DO 110 IP=NC+1,N 
      K(IP,3)=K(IP,3)+MIN(MSTJ(115)/2,1)+(MSTJ(115)/3)*(NC-1) 
  110 CONTINUE 
 
C...Angular orientation according to matrix element. 
      IF(MSTJ(106).EQ.1) THEN 
        CALL LUXDIF(NC,NJET,KFLC,ECMC,CHI,THE,PHI) 
        CALL LUDBRB(NC+1,N,0.,CHI,0D0,0D0,0D0) 
        CALL LUDBRB(NC+1,N,THE,PHI,0D0,0D0,0D0) 
      ENDIF 
 
C...Rotation and boost from radiative photon. 
      IF(MK.EQ.1) THEN 
        DBEK=-PAK/(ECM-PAK) 
        NMIN=NC+1-MSTJ(115)/3 
        CALL LUDBRB(NMIN,N,0.,-PHIK,0D0,0D0,0D0) 
        CALL LUDBRB(NMIN,N,ALPK,0.,DBEK*SIN(THEK),0D0,DBEK*COS(THEK)) 
        CALL LUDBRB(NMIN,N,0.,PHIK,0D0,0D0,0D0) 
      ENDIF 
 
C...Generate parton shower. Rearrange along strings and check. 
      IF(MSTJ(101).EQ.5) THEN 
        CALL LUSHOW(N-1,N,ECMC) 
        MSTJ14=MSTJ(14) 
        IF(MSTJ(105).EQ.-1) MSTJ(14)=-1 
        IF(MSTJ(105).GE.0) MSTU(28)=0 
        CALL LUPREP(0) 
        MSTJ(14)=MSTJ14 
        IF(MSTJ(105).GE.0.AND.MSTU(28).NE.0) GOTO 100 
      ENDIF 
 
C...Fragmentation/decay generation. Information for LUTABU. 
      IF(MSTJ(105).EQ.1) CALL LUEXEC 
      MSTU(161)=KFLC 
      MSTU(162)=-KFLC 
 
      RETURN 
      END