--- /dev/null
+* $Id$
+
+C*********************************************************************
+
+ SUBROUTINE LUDECY_HIJING(IP)
+
+C...Purpose: to handle the decay of unstable particles.
+#include "lujets_hijing.inc"
+#include "ludat1_hijing.inc"
+#include "ludat2_hijing.inc"
+#include "ludat3_hijing.inc"
+ DIMENSION VDCY(4),KFLO(4),KFL1(4),PV(10,5),RORD(10),UE(3),BE(3),
+ &WTCOR(10)
+ DATA WTCOR/2.,5.,15.,60.,250.,1500.,1.2E4,1.2E5,150.,16./
+
+C...Functions: momentum in two-particle decays, four-product and
+C...matrix element times phase space in weak decays.
+ PAWT(A,B,C)=SQRT((A**2-(B+C)**2)*(A**2-(B-C)**2))/(2.*A)
+ FOUR(I,J)=P(I,4)*P(J,4)-P(I,1)*P(J,1)-P(I,2)*P(J,2)-P(I,3)*P(J,3)
+ HMEPS(HA)=((1.-HRQ-HA)**2+3.*HA*(1.+HRQ-HA))*
+ &SQRT((1.-HRQ-HA)**2-4.*HRQ*HA)
+
+C...Initial values.
+ NTRY=0
+ NSAV=N
+ KFA=IABS(K(IP,2))
+ KFS=ISIGN(1,K(IP,2))
+ KC=LUCOMP_HIJING(KFA)
+ MSTJ(92)=0
+
+C...Choose lifetime and determine decay vertex.
+ IF(K(IP,1).EQ.5) THEN
+ V(IP,5)=0.
+ ELSEIF(K(IP,1).NE.4) THEN
+ V(IP,5)=-PMAS(KC,4)*LOG(RLU_HIJING(0))
+ ENDIF
+ DO 100 J=1,4
+ 100 VDCY(J)=V(IP,J)+V(IP,5)*P(IP,J)/P(IP,5)
+
+C...Determine whether decay allowed or not.
+ MOUT=0
+ IF(MSTJ(22).EQ.2) THEN
+ IF(PMAS(KC,4).GT.PARJ(71)) MOUT=1
+ ELSEIF(MSTJ(22).EQ.3) THEN
+ IF(VDCY(1)**2+VDCY(2)**2+VDCY(3)**2.GT.PARJ(72)**2) MOUT=1
+ ELSEIF(MSTJ(22).EQ.4) THEN
+ IF(VDCY(1)**2+VDCY(2)**2.GT.PARJ(73)**2) MOUT=1
+ IF(ABS(VDCY(3)).GT.PARJ(74)) MOUT=1
+ ENDIF
+ IF(MOUT.EQ.1.AND.K(IP,1).NE.5) THEN
+ K(IP,1)=4
+ RETURN
+ ENDIF
+
+C...Check existence of decay channels. Particle/antiparticle rules.
+ KCA=KC
+ IF(MDCY(KC,2).GT.0) THEN
+ MDMDCY=MDME(MDCY(KC,2),2)
+ IF(MDMDCY.GT.80.AND.MDMDCY.LE.90) KCA=MDMDCY
+ ENDIF
+ IF(MDCY(KCA,2).LE.0.OR.MDCY(KCA,3).LE.0) THEN
+ CALL LUERRM_HIJING(9
+ $ ,'(LUDECY_HIJING:) no decay channel defined')
+ RETURN
+ ENDIF
+ IF(MOD(KFA/1000,10).EQ.0.AND.(KCA.EQ.85.OR.KCA.EQ.87)) KFS=-KFS
+ IF(KCHG(KC,3).EQ.0) THEN
+ KFSP=1
+ KFSN=0
+ IF(RLU_HIJING(0).GT.0.5) KFS=-KFS
+ ELSEIF(KFS.GT.0) THEN
+ KFSP=1
+ KFSN=0
+ ELSE
+ KFSP=0
+ KFSN=1
+ ENDIF
+
+C...Sum branching ratios of allowed decay channels.
+ 110 NOPE=0
+ BRSU=0.
+ DO 120 IDL=MDCY(KCA,2),MDCY(KCA,2)+MDCY(KCA,3)-1
+ IF(MDME(IDL,1).NE.1.AND.KFSP*MDME(IDL,1).NE.2.AND.
+ &KFSN*MDME(IDL,1).NE.3) GOTO 120
+ IF(MDME(IDL,2).GT.100) GOTO 120
+ NOPE=NOPE+1
+ BRSU=BRSU+BRAT(IDL)
+ 120 CONTINUE
+ IF(NOPE.EQ.0) THEN
+ CALL LUERRM_HIJING(2
+ $ ,'(LUDECY_HIJING:) all decay channels closed by user')
+ RETURN
+ ENDIF
+
+C...Select decay channel among allowed ones.
+ 130 RBR=BRSU*RLU_HIJING(0)
+ IDL=MDCY(KCA,2)-1
+ 140 IDL=IDL+1
+ IF(MDME(IDL,1).NE.1.AND.KFSP*MDME(IDL,1).NE.2.AND.
+ &KFSN*MDME(IDL,1).NE.3) THEN
+ IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1) GOTO 140
+ ELSEIF(MDME(IDL,2).GT.100) THEN
+ IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1) GOTO 140
+ ELSE
+ IDC=IDL
+ RBR=RBR-BRAT(IDL)
+ IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1.AND.RBR.GT.0.) GOTO 140
+ ENDIF
+
+C...Start readout of decay channel: matrix element, reset counters.
+ MMAT=MDME(IDC,2)
+ 150 NTRY=NTRY+1
+ IF(NTRY.GT.1000) THEN
+ CALL LUERRM_HIJING(14
+ $ ,'(LUDECY_HIJING:) caught in infinite loop')
+ IF(MSTU(21).GE.1) RETURN
+ ENDIF
+ I=N
+ NP=0
+ NQ=0
+ MBST=0
+ IF(MMAT.GE.11.AND.MMAT.NE.46.AND.P(IP,4).GT.20.*P(IP,5)) MBST=1
+ DO 160 J=1,4
+ PV(1,J)=0.
+ 160 IF(MBST.EQ.0) PV(1,J)=P(IP,J)
+ IF(MBST.EQ.1) PV(1,4)=P(IP,5)
+ PV(1,5)=P(IP,5)
+ PS=0.
+ PSQ=0.
+ MREM=0
+
+C...Read out decay products. Convert to standard flavour code.
+ JTMAX=5
+ IF(MDME(IDC+1,2).EQ.101) JTMAX=10
+ DO 170 JT=1,JTMAX
+ IF(JT.LE.5) KP=KFDP(IDC,JT)
+ IF(JT.GE.6) KP=KFDP(IDC+1,JT-5)
+ IF(KP.EQ.0) GOTO 170
+ KPA=IABS(KP)
+ KCP=LUCOMP_HIJING(KPA)
+ IF(KCHG(KCP,3).EQ.0.AND.KPA.NE.81.AND.KPA.NE.82) THEN
+ KFP=KP
+ ELSEIF(KPA.NE.81.AND.KPA.NE.82) THEN
+ KFP=KFS*KP
+ ELSEIF(KPA.EQ.81.AND.MOD(KFA/1000,10).EQ.0) THEN
+ KFP=-KFS*MOD(KFA/10,10)
+ ELSEIF(KPA.EQ.81.AND.MOD(KFA/100,10).GE.MOD(KFA/10,10)) THEN
+ KFP=KFS*(100*MOD(KFA/10,100)+3)
+ ELSEIF(KPA.EQ.81) THEN
+ KFP=KFS*(1000*MOD(KFA/10,10)+100*MOD(KFA/100,10)+1)
+ ELSEIF(KP.EQ.82) THEN
+ CALL LUKFDI_HIJING(-KFS*INT(1.+(2.+PARJ(2))*RLU_HIJING(0)),0
+ $ ,KFP,KDUMP)
+ IF(KFP.EQ.0) GOTO 150
+ MSTJ(93)=1
+ IF(PV(1,5).LT.PARJ(32)+2.*ULMASS_HIJING(KFP)) GOTO 150
+ ELSEIF(KP.EQ.-82) THEN
+ KFP=-KFP
+ IF(IABS(KFP).GT.10) KFP=KFP+ISIGN(10000,KFP)
+ ENDIF
+ IF(KPA.EQ.81.OR.KPA.EQ.82) KCP=LUCOMP_HIJING(KFP)
+
+C...Add decay product to event record or to quark flavour list.
+ KFPA=IABS(KFP)
+ KQP=KCHG(KCP,2)
+ IF(MMAT.GE.11.AND.MMAT.LE.30.AND.KQP.NE.0) THEN
+ NQ=NQ+1
+ KFLO(NQ)=KFP
+ MSTJ(93)=2
+ PSQ=PSQ+ULMASS_HIJING(KFLO(NQ))
+ ELSEIF(MMAT.GE.42.AND.MMAT.LE.43.AND.NP.EQ.3.AND.MOD(NQ,2).EQ.1)
+ &THEN
+ NQ=NQ-1
+ PS=PS-P(I,5)
+ K(I,1)=1
+ KFI=K(I,2)
+ CALL LUKFDI_HIJING(KFP,KFI,KFLDMP,K(I,2))
+ IF(K(I,2).EQ.0) GOTO 150
+ MSTJ(93)=1
+ P(I,5)=ULMASS_HIJING(K(I,2))
+ PS=PS+P(I,5)
+ ELSE
+ I=I+1
+ NP=NP+1
+ IF(MMAT.NE.33.AND.KQP.NE.0) NQ=NQ+1
+ IF(MMAT.EQ.33.AND.KQP.NE.0.AND.KQP.NE.2) NQ=NQ+1
+ K(I,1)=1+MOD(NQ,2)
+ IF(MMAT.EQ.4.AND.JT.LE.2.AND.KFP.EQ.21) K(I,1)=2
+ IF(MMAT.EQ.4.AND.JT.EQ.3) K(I,1)=1
+ K(I,2)=KFP
+ K(I,3)=IP
+ K(I,4)=0
+ K(I,5)=0
+ P(I,5)=ULMASS_HIJING(KFP)
+ IF(MMAT.EQ.45.AND.KFPA.EQ.89) P(I,5)=PARJ(32)
+ PS=PS+P(I,5)
+ ENDIF
+ 170 CONTINUE
+
+C...Choose decay multiplicity in phase space model.
+ 180 IF(MMAT.GE.11.AND.MMAT.LE.30) THEN
+ PSP=PS
+ CNDE=PARJ(61)*LOG(MAX((PV(1,5)-PS-PSQ)/PARJ(62),1.1))
+ IF(MMAT.EQ.12) CNDE=CNDE+PARJ(63)
+ 190 NTRY=NTRY+1
+ IF(NTRY.GT.1000) THEN
+ CALL LUERRM_HIJING(14
+ $ ,'(LUDECY_HIJING:) caught in infinite loop')
+ IF(MSTU(21).GE.1) RETURN
+ ENDIF
+ IF(MMAT.LE.20) THEN
+ GAUSS=SQRT(-2.*CNDE*LOG(MAX(1E-10,RLU_HIJING(0))))*
+ & SIN(PARU(2)*RLU_HIJING(0))
+ ND=0.5+0.5*NP+0.25*NQ+CNDE+GAUSS
+ IF(ND.LT.NP+NQ/2.OR.ND.LT.2.OR.ND.GT.10) GOTO 190
+ IF(MMAT.EQ.13.AND.ND.EQ.2) GOTO 190
+ IF(MMAT.EQ.14.AND.ND.LE.3) GOTO 190
+ IF(MMAT.EQ.15.AND.ND.LE.4) GOTO 190
+ ELSE
+ ND=MMAT-20
+ ENDIF
+
+C...Form hadrons from flavour content.
+ DO 200 JT=1,4
+ 200 KFL1(JT)=KFLO(JT)
+ IF(ND.EQ.NP+NQ/2) GOTO 220
+ DO 210 I=N+NP+1,N+ND-NQ/2
+ JT=1+INT((NQ-1)*RLU_HIJING(0))
+ CALL LUKFDI_HIJING(KFL1(JT),0,KFL2,K(I,2))
+ IF(K(I,2).EQ.0) GOTO 190
+ 210 KFL1(JT)=-KFL2
+ 220 JT=2
+ JT2=3
+ JT3=4
+ IF(NQ.EQ.4.AND.RLU_HIJING(0).LT.PARJ(66)) JT=4
+ IF(JT.EQ.4.AND.ISIGN(1,KFL1(1)*(10-IABS(KFL1(1))))*
+ & ISIGN(1,KFL1(JT)*(10-IABS(KFL1(JT)))).GT.0) JT=3
+ IF(JT.EQ.3) JT2=2
+ IF(JT.EQ.4) JT3=2
+ CALL LUKFDI_HIJING(KFL1(1),KFL1(JT),KFLDMP,K(N+ND-NQ/2+1,2))
+ IF(K(N+ND-NQ/2+1,2).EQ.0) GOTO 190
+ IF(NQ.EQ.4) CALL LUKFDI_HIJING(KFL1(JT2),KFL1(JT3),KFLDMP,K(N+ND
+ $ ,2))
+ IF(NQ.EQ.4.AND.K(N+ND,2).EQ.0) GOTO 190
+
+C...Check that sum of decay product masses not too large.
+ PS=PSP
+ DO 230 I=N+NP+1,N+ND
+ K(I,1)=1
+ K(I,3)=IP
+ K(I,4)=0
+ K(I,5)=0
+ P(I,5)=ULMASS_HIJING(K(I,2))
+ 230 PS=PS+P(I,5)
+ IF(PS+PARJ(64).GT.PV(1,5)) GOTO 190
+
+C...Rescale energy to subtract off spectator quark mass.
+ ELSEIF((MMAT.EQ.31.OR.MMAT.EQ.33.OR.MMAT.EQ.44.OR.MMAT.EQ.45).
+ &AND.NP.GE.3) THEN
+ PS=PS-P(N+NP,5)
+ PQT=(P(N+NP,5)+PARJ(65))/PV(1,5)
+ DO 240 J=1,5
+ P(N+NP,J)=PQT*PV(1,J)
+ 240 PV(1,J)=(1.-PQT)*PV(1,J)
+ IF(PS+PARJ(64).GT.PV(1,5)) GOTO 150
+ ND=NP-1
+ MREM=1
+
+C...Phase space factors imposed in W decay.
+ ELSEIF(MMAT.EQ.46) THEN
+ MSTJ(93)=1
+ PSMC=ULMASS_HIJING(K(N+1,2))
+ MSTJ(93)=1
+ PSMC=PSMC+ULMASS_HIJING(K(N+2,2))
+ IF(MAX(PS,PSMC)+PARJ(32).GT.PV(1,5)) GOTO 130
+ HR1=(P(N+1,5)/PV(1,5))**2
+ HR2=(P(N+2,5)/PV(1,5))**2
+ IF((1.-HR1-HR2)*(2.+HR1+HR2)*SQRT((1.-HR1-HR2)**2-4.*HR1*HR2).
+ & LT.2.*RLU_HIJING(0)) GOTO 130
+ ND=NP
+
+C...Fully specified final state: check mass broadening effects.
+ ELSE
+ IF(NP.GE.2.AND.PS+PARJ(64).GT.PV(1,5)) GOTO 150
+ ND=NP
+ ENDIF
+
+C...Select W mass in decay Q -> W + q, without W propagator.
+ IF(MMAT.EQ.45.AND.MSTJ(25).LE.0) THEN
+ HLQ=(PARJ(32)/PV(1,5))**2
+ HUQ=(1.-(P(N+2,5)+PARJ(64))/PV(1,5))**2
+ HRQ=(P(N+2,5)/PV(1,5))**2
+ 250 HW=HLQ+RLU_HIJING(0)*(HUQ-HLQ)
+ IF(HMEPS(HW).LT.RLU_HIJING(0)) GOTO 250
+ P(N+1,5)=PV(1,5)*SQRT(HW)
+
+C...Ditto, including W propagator. Divide mass range into three regions.
+ ELSEIF(MMAT.EQ.45) THEN
+ HQW=(PV(1,5)/PMAS(24,1))**2
+ HLW=(PARJ(32)/PMAS(24,1))**2
+ HUW=((PV(1,5)-P(N+2,5)-PARJ(64))/PMAS(24,1))**2
+ HRQ=(P(N+2,5)/PV(1,5))**2
+ HG=PMAS(24,2)/PMAS(24,1)
+ HATL=ATAN((HLW-1.)/HG)
+ HM=MIN(1.,HUW-0.001)
+ HMV1=HMEPS(HM/HQW)/((HM-1.)**2+HG**2)
+ 260 HM=HM-HG
+ HMV2=HMEPS(HM/HQW)/((HM-1.)**2+HG**2)
+ HSAV1=HMEPS(HM/HQW)
+ HSAV2=1./((HM-1.)**2+HG**2)
+ IF(HMV2.GT.HMV1.AND.HM-HG.GT.HLW) THEN
+ HMV1=HMV2
+ GOTO 260
+ ENDIF
+ HMV=MIN(2.*HMV1,HMEPS(HM/HQW)/HG**2)
+ HM1=1.-SQRT(1./HMV-HG**2)
+ IF(HM1.GT.HLW.AND.HM1.LT.HM) THEN
+ HM=HM1
+ ELSEIF(HMV2.LE.HMV1) THEN
+ HM=MAX(HLW,HM-MIN(0.1,1.-HM))
+ ENDIF
+ HATM=ATAN((HM-1.)/HG)
+ HWT1=(HATM-HATL)/HG
+ HWT2=HMV*(MIN(1.,HUW)-HM)
+ HWT3=0.
+ IF(HUW.GT.1.) THEN
+ HATU=ATAN((HUW-1.)/HG)
+ HMP1=HMEPS(1./HQW)
+ HWT3=HMP1*HATU/HG
+ ENDIF
+
+C...Select mass region and W mass there. Accept according to weight.
+ 270 HREG=RLU_HIJING(0)*(HWT1+HWT2+HWT3)
+ IF(HREG.LE.HWT1) THEN
+ HW=1.+HG*TAN(HATL+RLU_HIJING(0)*(HATM-HATL))
+ HACC=HMEPS(HW/HQW)
+ ELSEIF(HREG.LE.HWT1+HWT2) THEN
+ HW=HM+RLU_HIJING(0)*(MIN(1.,HUW)-HM)
+ HACC=HMEPS(HW/HQW)/((HW-1.)**2+HG**2)/HMV
+ ELSE
+ HW=1.+HG*TAN(RLU_HIJING(0)*HATU)
+ HACC=HMEPS(HW/HQW)/HMP1
+ ENDIF
+ IF(HACC.LT.RLU_HIJING(0)) GOTO 270
+ P(N+1,5)=PMAS(24,1)*SQRT(HW)
+ ENDIF
+
+C...Determine position of grandmother, number of sisters, Q -> W sign.
+ NM=0
+ MSGN=0
+ IF(MMAT.EQ.3.OR.MMAT.EQ.46) THEN
+ IM=K(IP,3)
+ IF(IM.LT.0.OR.IM.GE.IP) IM=0
+ IF(IM.NE.0) KFAM=IABS(K(IM,2))
+ IF(IM.NE.0.AND.MMAT.EQ.3) THEN
+ DO 280 IL=MAX(IP-2,IM+1),MIN(IP+2,N)
+ 280 IF(K(IL,3).EQ.IM) NM=NM+1
+ IF(NM.NE.2.OR.KFAM.LE.100.OR.MOD(KFAM,10).NE.1.OR.
+ & MOD(KFAM/1000,10).NE.0) NM=0
+ ELSEIF(IM.NE.0.AND.MMAT.EQ.46) THEN
+ MSGN=ISIGN(1,K(IM,2)*K(IP,2))
+ IF(KFAM.GT.100.AND.MOD(KFAM/1000,10).EQ.0) MSGN=
+ & MSGN*(-1)**MOD(KFAM/100,10)
+ ENDIF
+ ENDIF
+
+C...Kinematics of one-particle decays.
+ IF(ND.EQ.1) THEN
+ DO 290 J=1,4
+ 290 P(N+1,J)=P(IP,J)
+ GOTO 510
+ ENDIF
+
+C...Calculate maximum weight ND-particle decay.
+ PV(ND,5)=P(N+ND,5)
+ IF(ND.GE.3) THEN
+ WTMAX=1./WTCOR(ND-2)
+ PMAX=PV(1,5)-PS+P(N+ND,5)
+ PMIN=0.
+ DO 300 IL=ND-1,1,-1
+ PMAX=PMAX+P(N+IL,5)
+ PMIN=PMIN+P(N+IL+1,5)
+ 300 WTMAX=WTMAX*PAWT(PMAX,PMIN,P(N+IL,5))
+ ENDIF
+
+C...Find virtual gamma mass in Dalitz decay.
+ 310 IF(ND.EQ.2) THEN
+ ELSEIF(MMAT.EQ.2) THEN
+ PMES=4.*PMAS(11,1)**2
+ PMRHO2=PMAS(131,1)**2
+ PGRHO2=PMAS(131,2)**2
+ 320 PMST=PMES*(P(IP,5)**2/PMES)**RLU_HIJING(0)
+ WT=(1+0.5*PMES/PMST)*SQRT(MAX(0.,1.-PMES/PMST))*
+ & (1.-PMST/P(IP,5)**2)**3*(1.+PGRHO2/PMRHO2)/
+ & ((1.-PMST/PMRHO2)**2+PGRHO2/PMRHO2)
+ IF(WT.LT.RLU_HIJING(0)) GOTO 320
+ PV(2,5)=MAX(2.00001*PMAS(11,1),SQRT(PMST))
+
+C...M-generator gives weight. If rejected, try again.
+ ELSE
+ 330 RORD(1)=1.
+ DO 350 IL1=2,ND-1
+ RSAV=RLU_HIJING(0)
+ DO 340 IL2=IL1-1,1,-1
+ IF(RSAV.LE.RORD(IL2)) GOTO 350
+ 340 RORD(IL2+1)=RORD(IL2)
+ 350 RORD(IL2+1)=RSAV
+ RORD(ND)=0.
+ WT=1.
+ DO 360 IL=ND-1,1,-1
+ PV(IL,5)=PV(IL+1,5)+P(N+IL,5)+(RORD(IL)-RORD(IL+1))*(PV(1,5)-PS)
+ 360 WT=WT*PAWT(PV(IL,5),PV(IL+1,5),P(N+IL,5))
+ IF(WT.LT.RLU_HIJING(0)*WTMAX) GOTO 330
+ ENDIF
+
+C...Perform two-particle decays in respective CM frame.
+ 370 DO 390 IL=1,ND-1
+ PA=PAWT(PV(IL,5),PV(IL+1,5),P(N+IL,5))
+ UE(3)=2.*RLU_HIJING(0)-1.
+ PHI=PARU(2)*RLU_HIJING(0)
+ UE(1)=SQRT(1.-UE(3)**2)*COS(PHI)
+ UE(2)=SQRT(1.-UE(3)**2)*SIN(PHI)
+ DO 380 J=1,3
+ P(N+IL,J)=PA*UE(J)
+ 380 PV(IL+1,J)=-PA*UE(J)
+ P(N+IL,4)=SQRT(PA**2+P(N+IL,5)**2)
+ 390 PV(IL+1,4)=SQRT(PA**2+PV(IL+1,5)**2)
+
+C...Lorentz transform decay products to lab frame.
+ DO 400 J=1,4
+ 400 P(N+ND,J)=PV(ND,J)
+ DO 430 IL=ND-1,1,-1
+ DO 410 J=1,3
+ 410 BE(J)=PV(IL,J)/PV(IL,4)
+ GA=PV(IL,4)/PV(IL,5)
+ DO 430 I=N+IL,N+ND
+ BEP=BE(1)*P(I,1)+BE(2)*P(I,2)+BE(3)*P(I,3)
+ DO 420 J=1,3
+ 420 P(I,J)=P(I,J)+GA*(GA*BEP/(1.+GA)+P(I,4))*BE(J)
+ 430 P(I,4)=GA*(P(I,4)+BEP)
+
+C...Matrix elements for omega and phi decays.
+ IF(MMAT.EQ.1) THEN
+ WT=(P(N+1,5)*P(N+2,5)*P(N+3,5))**2-(P(N+1,5)*FOUR(N+2,N+3))**2
+ & -(P(N+2,5)*FOUR(N+1,N+3))**2-(P(N+3,5)*FOUR(N+1,N+2))**2
+ & +2.*FOUR(N+1,N+2)*FOUR(N+1,N+3)*FOUR(N+2,N+3)
+ IF(MAX(WT*WTCOR(9)/P(IP,5)**6,0.001).LT.RLU_HIJING(0)) GOTO 310
+
+C...Matrix elements for pi0 or eta Dalitz decay to gamma e+ e-.
+ ELSEIF(MMAT.EQ.2) THEN
+ FOUR12=FOUR(N+1,N+2)
+ FOUR13=FOUR(N+1,N+3)
+ FOUR23=0.5*PMST-0.25*PMES
+ WT=(PMST-0.5*PMES)*(FOUR12**2+FOUR13**2)+
+ & PMES*(FOUR12*FOUR13+FOUR12**2+FOUR13**2)
+ IF(WT.LT.RLU_HIJING(0)*0.25*PMST*(P(IP,5)**2-PMST)**2) GOTO 370
+
+C...Matrix element for S0 -> S1 + V1 -> S1 + S2 + S3 (S scalar,
+C...V vector), of form cos**2(theta02) in V1 rest frame.
+ ELSEIF(MMAT.EQ.3.AND.NM.EQ.2) THEN
+ IF((P(IP,5)**2*FOUR(IM,N+1)-FOUR(IP,IM)*FOUR(IP,N+1))**2.LE.
+ & RLU_HIJING(0)*(FOUR(IP,IM)**2-(P(IP,5)*P(IM,5))**2)
+ $ *(FOUR(IP,N+1)**2-(P(IP,5)*P(N+1,5))**2)) GOTO 370
+
+C...Matrix element for "onium" -> g + g + g or gamma + g + g.
+ ELSEIF(MMAT.EQ.4) THEN
+ HX1=2.*FOUR(IP,N+1)/P(IP,5)**2
+ HX2=2.*FOUR(IP,N+2)/P(IP,5)**2
+ HX3=2.*FOUR(IP,N+3)/P(IP,5)**2
+ WT=((1.-HX1)/(HX2*HX3))**2+((1.-HX2)/(HX1*HX3))**2+
+ & ((1.-HX3)/(HX1*HX2))**2
+ IF(WT.LT.2.*RLU_HIJING(0)) GOTO 310
+ IF(K(IP+1,2).EQ.22.AND.(1.-HX1)*P(IP,5)**2.LT.4.*PARJ(32)**2)
+ & GOTO 310
+
+C...Effective matrix element for nu spectrum in tau -> nu + hadrons.
+ ELSEIF(MMAT.EQ.41) THEN
+ HX1=2.*FOUR(IP,N+1)/P(IP,5)**2
+ IF(8.*HX1*(3.-2.*HX1)/9..LT.RLU_HIJING(0)) GOTO 310
+
+C...Matrix elements for weak decays (only semileptonic for c and b)
+ ELSEIF(MMAT.GE.42.AND.MMAT.LE.44.AND.ND.EQ.3) THEN
+ IF(MBST.EQ.0) WT=FOUR(IP,N+1)*FOUR(N+2,N+3)
+ IF(MBST.EQ.1) WT=P(IP,5)*P(N+1,4)*FOUR(N+2,N+3)
+ IF(WT.LT.RLU_HIJING(0)*P(IP,5)*PV(1,5)**3/WTCOR(10)) GOTO 310
+ ELSEIF(MMAT.GE.42.AND.MMAT.LE.44) THEN
+ DO 440 J=1,4
+ P(N+NP+1,J)=0.
+ DO 440 IS=N+3,N+NP
+ 440 P(N+NP+1,J)=P(N+NP+1,J)+P(IS,J)
+ IF(MBST.EQ.0) WT=FOUR(IP,N+1)*FOUR(N+2,N+NP+1)
+ IF(MBST.EQ.1) WT=P(IP,5)*P(N+1,4)*FOUR(N+2,N+NP+1)
+ IF(WT.LT.RLU_HIJING(0)*P(IP,5)*PV(1,5)**3/WTCOR(10)) GOTO 310
+
+C...Angular distribution in W decay.
+ ELSEIF(MMAT.EQ.46.AND.MSGN.NE.0) THEN
+ IF(MSGN.GT.0) WT=FOUR(IM,N+1)*FOUR(N+2,IP+1)
+ IF(MSGN.LT.0) WT=FOUR(IM,N+2)*FOUR(N+1,IP+1)
+ IF(WT.LT.RLU_HIJING(0)*P(IM,5)**4/WTCOR(10)) GOTO 370
+ ENDIF
+
+C...Scale back energy and reattach spectator.
+ IF(MREM.EQ.1) THEN
+ DO 450 J=1,5
+ 450 PV(1,J)=PV(1,J)/(1.-PQT)
+ ND=ND+1
+ MREM=0
+ ENDIF
+
+C...Low invariant mass for system with spectator quark gives particle,
+C...not two jets. Readjust momenta accordingly.
+ IF((MMAT.EQ.31.OR.MMAT.EQ.45).AND.ND.EQ.3) THEN
+ MSTJ(93)=1
+ PM2=ULMASS_HIJING(K(N+2,2))
+ MSTJ(93)=1
+ PM3=ULMASS_HIJING(K(N+3,2))
+ IF(P(N+2,5)**2+P(N+3,5)**2+2.*FOUR(N+2,N+3).GE.
+ & (PARJ(32)+PM2+PM3)**2) GOTO 510
+ K(N+2,1)=1
+ KFTEMP=K(N+2,2)
+ CALL LUKFDI_HIJING(KFTEMP,K(N+3,2),KFLDMP,K(N+2,2))
+ IF(K(N+2,2).EQ.0) GOTO 150
+ P(N+2,5)=ULMASS_HIJING(K(N+2,2))
+ PS=P(N+1,5)+P(N+2,5)
+ PV(2,5)=P(N+2,5)
+ MMAT=0
+ ND=2
+ GOTO 370
+ ELSEIF(MMAT.EQ.44) THEN
+ MSTJ(93)=1
+ PM3=ULMASS_HIJING(K(N+3,2))
+ MSTJ(93)=1
+ PM4=ULMASS_HIJING(K(N+4,2))
+ IF(P(N+3,5)**2+P(N+4,5)**2+2.*FOUR(N+3,N+4).GE.
+ & (PARJ(32)+PM3+PM4)**2) GOTO 480
+ K(N+3,1)=1
+ KFTEMP=K(N+3,2)
+ CALL LUKFDI_HIJING(KFTEMP,K(N+4,2),KFLDMP,K(N+3,2))
+ IF(K(N+3,2).EQ.0) GOTO 150
+ P(N+3,5)=ULMASS_HIJING(K(N+3,2))
+ DO 460 J=1,3
+ 460 P(N+3,J)=P(N+3,J)+P(N+4,J)
+ P(N+3,4)=SQRT(P(N+3,1)**2+P(N+3,2)**2+P(N+3,3)**2+P(N+3,5)**2)
+ HA=P(N+1,4)**2-P(N+2,4)**2
+ HB=HA-(P(N+1,5)**2-P(N+2,5)**2)
+ HC=(P(N+1,1)-P(N+2,1))**2+(P(N+1,2)-P(N+2,2))**2+
+ & (P(N+1,3)-P(N+2,3))**2
+ HD=(PV(1,4)-P(N+3,4))**2
+ HE=HA**2-2.*HD*(P(N+1,4)**2+P(N+2,4)**2)+HD**2
+ HF=HD*HC-HB**2
+ HG=HD*HC-HA*HB
+ HH=(SQRT(HG**2+HE*HF)-HG)/(2.*HF)
+ DO 470 J=1,3
+ PCOR=HH*(P(N+1,J)-P(N+2,J))
+ P(N+1,J)=P(N+1,J)+PCOR
+ 470 P(N+2,J)=P(N+2,J)-PCOR
+ P(N+1,4)=SQRT(P(N+1,1)**2+P(N+1,2)**2+P(N+1,3)**2+P(N+1,5)**2)
+ P(N+2,4)=SQRT(P(N+2,1)**2+P(N+2,2)**2+P(N+2,3)**2+P(N+2,5)**2)
+ ND=ND-1
+ ENDIF
+
+C...Check invariant mass of W jets. May give one particle or start over.
+ 480 IF(MMAT.GE.42.AND.MMAT.LE.44.AND.IABS(K(N+1,2)).LT.10) THEN
+ PMR=SQRT(MAX(0.,P(N+1,5)**2+P(N+2,5)**2+2.*FOUR(N+1,N+2)))
+ MSTJ(93)=1
+ PM1=ULMASS_HIJING(K(N+1,2))
+ MSTJ(93)=1
+ PM2=ULMASS_HIJING(K(N+2,2))
+ IF(PMR.GT.PARJ(32)+PM1+PM2) GOTO 490
+ KFLDUM=INT(1.5+RLU_HIJING(0))
+ CALL LUKFDI_HIJING(K(N+1,2),-ISIGN(KFLDUM,K(N+1,2)),KFLDMP,KF1)
+ CALL LUKFDI_HIJING(K(N+2,2),-ISIGN(KFLDUM,K(N+2,2)),KFLDMP,KF2)
+ IF(KF1.EQ.0.OR.KF2.EQ.0) GOTO 150
+ PSM=ULMASS_HIJING(KF1)+ULMASS_HIJING(KF2)
+ IF(MMAT.EQ.42.AND.PMR.GT.PARJ(64)+PSM) GOTO 490
+ IF(MMAT.GE.43.AND.PMR.GT.0.2*PARJ(32)+PSM) GOTO 490
+ IF(ND.EQ.4.OR.KFA.EQ.15) GOTO 150
+ K(N+1,1)=1
+ KFTEMP=K(N+1,2)
+ CALL LUKFDI_HIJING(KFTEMP,K(N+2,2),KFLDMP,K(N+1,2))
+ IF(K(N+1,2).EQ.0) GOTO 150
+ P(N+1,5)=ULMASS_HIJING(K(N+1,2))
+ K(N+2,2)=K(N+3,2)
+ P(N+2,5)=P(N+3,5)
+ PS=P(N+1,5)+P(N+2,5)
+ PV(2,5)=P(N+3,5)
+ MMAT=0
+ ND=2
+ GOTO 370
+ ENDIF
+
+C...Phase space decay of partons from W decay.
+ 490 IF(MMAT.EQ.42.AND.IABS(K(N+1,2)).LT.10) THEN
+ KFLO(1)=K(N+1,2)
+ KFLO(2)=K(N+2,2)
+ K(N+1,1)=K(N+3,1)
+ K(N+1,2)=K(N+3,2)
+ DO 500 J=1,5
+ PV(1,J)=P(N+1,J)+P(N+2,J)
+ 500 P(N+1,J)=P(N+3,J)
+ PV(1,5)=PMR
+ N=N+1
+ NP=0
+ NQ=2
+ PS=0.
+ MSTJ(93)=2
+ PSQ=ULMASS_HIJING(KFLO(1))
+ MSTJ(93)=2
+ PSQ=PSQ+ULMASS_HIJING(KFLO(2))
+ MMAT=11
+ GOTO 180
+ ENDIF
+
+C...Boost back for rapidly moving particle.
+ 510 N=N+ND
+ IF(MBST.EQ.1) THEN
+ DO 520 J=1,3
+ 520 BE(J)=P(IP,J)/P(IP,4)
+ GA=P(IP,4)/P(IP,5)
+ DO 540 I=NSAV+1,N
+ BEP=BE(1)*P(I,1)+BE(2)*P(I,2)+BE(3)*P(I,3)
+ DO 530 J=1,3
+ 530 P(I,J)=P(I,J)+GA*(GA*BEP/(1.+GA)+P(I,4))*BE(J)
+ 540 P(I,4)=GA*(P(I,4)+BEP)
+ ENDIF
+
+C...Fill in position of decay vertex.
+ DO 560 I=NSAV+1,N
+ DO 550 J=1,4
+ 550 V(I,J)=VDCY(J)
+ 560 V(I,5)=0.
+
+C...Set up for parton shower evolution from jets.
+ IF(MSTJ(23).GE.1.AND.MMAT.EQ.4.AND.K(NSAV+1,2).EQ.21) THEN
+ K(NSAV+1,1)=3
+ K(NSAV+2,1)=3
+ K(NSAV+3,1)=3
+ K(NSAV+1,4)=MSTU(5)*(NSAV+2)
+ K(NSAV+1,5)=MSTU(5)*(NSAV+3)
+ K(NSAV+2,4)=MSTU(5)*(NSAV+3)
+ K(NSAV+2,5)=MSTU(5)*(NSAV+1)
+ K(NSAV+3,4)=MSTU(5)*(NSAV+1)
+ K(NSAV+3,5)=MSTU(5)*(NSAV+2)
+ MSTJ(92)=-(NSAV+1)
+ ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.4) THEN
+ K(NSAV+2,1)=3
+ K(NSAV+3,1)=3
+ K(NSAV+2,4)=MSTU(5)*(NSAV+3)
+ K(NSAV+2,5)=MSTU(5)*(NSAV+3)
+ K(NSAV+3,4)=MSTU(5)*(NSAV+2)
+ K(NSAV+3,5)=MSTU(5)*(NSAV+2)
+ MSTJ(92)=NSAV+2
+ ELSEIF(MSTJ(23).GE.1.AND.(MMAT.EQ.32.OR.MMAT.EQ.44.OR.MMAT.EQ.46).
+ &AND.IABS(K(NSAV+1,2)).LE.10.AND.IABS(K(NSAV+2,2)).LE.10) THEN
+ K(NSAV+1,1)=3
+ K(NSAV+2,1)=3
+ K(NSAV+1,4)=MSTU(5)*(NSAV+2)
+ K(NSAV+1,5)=MSTU(5)*(NSAV+2)
+ K(NSAV+2,4)=MSTU(5)*(NSAV+1)
+ K(NSAV+2,5)=MSTU(5)*(NSAV+1)
+ MSTJ(92)=NSAV+1
+ ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.33.AND.IABS(K(NSAV+2,2)).EQ.21)
+ &THEN
+ K(NSAV+1,1)=3
+ K(NSAV+2,1)=3
+ K(NSAV+3,1)=3
+ KCP=LUCOMP_HIJING(K(NSAV+1,2))
+ KQP=KCHG(KCP,2)*ISIGN(1,K(NSAV+1,2))
+ JCON=4
+ IF(KQP.LT.0) JCON=5
+ K(NSAV+1,JCON)=MSTU(5)*(NSAV+2)
+ K(NSAV+2,9-JCON)=MSTU(5)*(NSAV+1)
+ K(NSAV+2,JCON)=MSTU(5)*(NSAV+3)
+ K(NSAV+3,9-JCON)=MSTU(5)*(NSAV+2)
+ MSTJ(92)=NSAV+1
+ ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.33) THEN
+ K(NSAV+1,1)=3
+ K(NSAV+3,1)=3
+ K(NSAV+1,4)=MSTU(5)*(NSAV+3)
+ K(NSAV+1,5)=MSTU(5)*(NSAV+3)
+ K(NSAV+3,4)=MSTU(5)*(NSAV+1)
+ K(NSAV+3,5)=MSTU(5)*(NSAV+1)
+ MSTJ(92)=NSAV+1
+ ENDIF
+
+C...Mark decayed particle.
+ IF(K(IP,1).EQ.5) K(IP,1)=15
+ IF(K(IP,1).LE.10) K(IP,1)=11
+ K(IP,4)=NSAV+1
+ K(IP,5)=N
+
+ RETURN
+ END
git://git.uio.no / u / mrichter / AliRoot.git / blobdiff