hijing/src/luxkfl.f

0001
0002 C*********************************************************************
0003
0004       SUBROUTINE LUXKFL(KFL,ECM,ECMC,KFLC)
0005
0006 C...Purpose: to select flavour for produced qqbar pair.
0007       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
0008       SAVE /LUDAT1/
0009       COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
0010       SAVE /LUDAT2/
0011
0012 C...Calculate maximum weight in QED or QFD case.
0013       IF(MSTJ(102).LE.1) THEN
0014         RFMAX=4./9.
0015       ELSE
0016         POLL=1.-PARJ(131)*PARJ(132)
0017         SFF=1./(16.*PARU(102)*(1.-PARU(102)))
0018         SFW=ECMC**4/((ECMC**2-PARJ(123)**2)**2+(PARJ(123)*PARJ(124))**2)
0019         SFI=SFW*(1.-(PARJ(123)/ECMC)**2)
0020         VE=4.*PARU(102)-1.
0021         HF1I=SFI*SFF*(VE*POLL+PARJ(132)-PARJ(131))
0022         HF1W=SFW*SFF**2*((VE**2+1.)*POLL+2.*VE*(PARJ(132)-PARJ(131)))
0023         RFMAX=MAX(4./9.*POLL-4./3.*(1.-8.*PARU(102)/3.)*HF1I+
0024      &  ((1.-8.*PARU(102)/3.)**2+1.)*HF1W,1./9.*POLL+2./3.*
0025      &  (-1.+4.*PARU(102)/3.)*HF1I+((-1.+4.*PARU(102)/3.)**2+1.)*HF1W)
0026       ENDIF
0027
0028 C...Choose flavour. Gives charge and velocity.
0029       NTRY=0
0030   100 NTRY=NTRY+1
0031       IF(NTRY.GT.100) THEN
0032         CALL LUERRM(14,'(LUXKFL:) caught in an infinite loop')
0033         KFLC=0
0034         RETURN
0035       ENDIF
0036       KFLC=KFL
0037       IF(KFL.LE.0) KFLC=1+INT(MSTJ(104)*RLU(0))
0038       MSTJ(93)=1
0039       PMQ=ULMASS(KFLC)
0040       IF(ECM.LT.2.*PMQ+PARJ(127)) GOTO 100
0041       QF=KCHG(KFLC,1)/3.
0042       VQ=1.
0043       IF(MOD(MSTJ(103),2).EQ.1) VQ=SQRT(MAX(0.,1.-(2.*PMQ/ECMC)**2))
0044
0045 C...Calculate weight in QED or QFD case.
0046       IF(MSTJ(102).LE.1) THEN
0047         RF=QF**2
0048         RFV=0.5*VQ*(3.-VQ**2)*QF**2
0049       ELSE
0050         VF=SIGN(1.,QF)-4.*QF*PARU(102)
0051         RF=QF**2*POLL-2.*QF*VF*HF1I+(VF**2+1.)*HF1W
0052         RFV=0.5*VQ*(3.-VQ**2)*(QF**2*POLL-2.*QF*VF*HF1I+VF**2*HF1W)+
0053      &  VQ**3*HF1W
0054       ENDIF
0055
0056 C...Weighting or new event (radiative photon). Cross-section update.
0057       IF(KFL.LE.0.AND.RF.LT.RLU(0)*RFMAX) GOTO 100
0058       PARJ(158)=PARJ(158)+1.
0059       IF(ECMC.LT.2.*PMQ+PARJ(127).OR.RFV.LT.RLU(0)*RF) KFLC=0
0060       IF(MSTJ(107).LE.0.AND.KFLC.EQ.0) GOTO 100
0061       IF(KFLC.NE.0) PARJ(159)=PARJ(159)+1.
0062       PARJ(144)=PARJ(157)*PARJ(159)/PARJ(158)
0063       PARJ(148)=PARJ(144)*86.8/ECM**2
0064
0065       RETURN
0066       END