HIJING/hipyset1_35/ludecy_hijing.F

   1 * $Id$
   2
   3 C*********************************************************************
   4
   5       SUBROUTINE LUDECY_HIJING(IP)
   6
   7 C...Purpose: to handle the decay of unstable particles.
   8 #include "lujets_hijing.inc"
   9 #include "ludat1_hijing.inc"
  10 #include "ludat2_hijing.inc"
  11 #include "ludat3_hijing.inc"
  12       DIMENSION VDCY(4),KFLO(4),KFL1(4),PV(10,5),RORD(10),UE(3),BE(3),
  13      &WTCOR(10)
  14       DATA WTCOR/2.,5.,15.,60.,250.,1500.,1.2E4,1.2E5,150.,16./
  15
  16 C...Functions: momentum in two-particle decays, four-product and
  17 C...matrix element times phase space in weak decays.
  18       PAWT(A,B,C)=SQRT((A**2-(B+C)**2)*(A**2-(B-C)**2))/(2.*A)
  19       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)
  20       HMEPS(HA)=((1.-HRQ-HA)**2+3.*HA*(1.+HRQ-HA))*
  21      &SQRT((1.-HRQ-HA)**2-4.*HRQ*HA)
  22
  23 C...Initial values.
  24       NTRY=0
  25       NSAV=N
  26       KFA=IABS(K(IP,2))
  27       KFS=ISIGN(1,K(IP,2))
  28       KC=LUCOMP_HIJING(KFA)
  29       MSTJ(92)=0
  30
  31 C...Choose lifetime and determine decay vertex.
  32       IF(K(IP,1).EQ.5) THEN
  33         V(IP,5)=0.
  34       ELSEIF(K(IP,1).NE.4) THEN
  35         V(IP,5)=-PMAS(KC,4)*LOG(RLU_HIJING(0))
  36       ENDIF
  37       DO 100 J=1,4
  38   100 VDCY(J)=V(IP,J)+V(IP,5)*P(IP,J)/P(IP,5)
  39
  40 C...Determine whether decay allowed or not.
  41       MOUT=0
  42       IF(MSTJ(22).EQ.2) THEN
  43         IF(PMAS(KC,4).GT.PARJ(71)) MOUT=1
  44       ELSEIF(MSTJ(22).EQ.3) THEN
  45         IF(VDCY(1)**2+VDCY(2)**2+VDCY(3)**2.GT.PARJ(72)**2) MOUT=1
  46       ELSEIF(MSTJ(22).EQ.4) THEN
  47         IF(VDCY(1)**2+VDCY(2)**2.GT.PARJ(73)**2) MOUT=1
  48         IF(ABS(VDCY(3)).GT.PARJ(74)) MOUT=1
  49       ENDIF
  50       IF(MOUT.EQ.1.AND.K(IP,1).NE.5) THEN
  51         K(IP,1)=4
  52         RETURN
  53       ENDIF
  54
  55 C...Check existence of decay channels. Particle/antiparticle rules.
  56       KCA=KC
  57       IF(MDCY(KC,2).GT.0) THEN
  58         MDMDCY=MDME(MDCY(KC,2),2)
  59         IF(MDMDCY.GT.80.AND.MDMDCY.LE.90) KCA=MDMDCY
  60       ENDIF
  61       IF(MDCY(KCA,2).LE.0.OR.MDCY(KCA,3).LE.0) THEN
  62          CALL LUERRM_HIJING(9
  63      $        ,'(LUDECY_HIJING:) no decay channel defined')
  64         RETURN
  65       ENDIF
  66       IF(MOD(KFA/1000,10).EQ.0.AND.(KCA.EQ.85.OR.KCA.EQ.87)) KFS=-KFS
  67       IF(KCHG(KC,3).EQ.0) THEN
  68         KFSP=1
  69         KFSN=0
  70         IF(RLU_HIJING(0).GT.0.5) KFS=-KFS
  71       ELSEIF(KFS.GT.0) THEN
  72         KFSP=1
  73         KFSN=0
  74       ELSE
  75         KFSP=0
  76         KFSN=1
  77       ENDIF
  78
  79 C...Sum branching ratios of allowed decay channels.
  80   110 NOPE=0
  81       BRSU=0.
  82       DO 120 IDL=MDCY(KCA,2),MDCY(KCA,2)+MDCY(KCA,3)-1
  83       IF(MDME(IDL,1).NE.1.AND.KFSP*MDME(IDL,1).NE.2.AND.
  84      &KFSN*MDME(IDL,1).NE.3) GOTO 120
  85       IF(MDME(IDL,2).GT.100) GOTO 120
  86       NOPE=NOPE+1
  87       BRSU=BRSU+BRAT(IDL)
  88   120 CONTINUE
  89       IF(NOPE.EQ.0) THEN
  90          CALL LUERRM_HIJING(2
  91      $        ,'(LUDECY_HIJING:) all decay channels closed by user')
  92         RETURN
  93       ENDIF
  94
  95 C...Select decay channel among allowed ones.
  96   130 RBR=BRSU*RLU_HIJING(0)
  97       IDL=MDCY(KCA,2)-1
  98   140 IDL=IDL+1
  99       IF(MDME(IDL,1).NE.1.AND.KFSP*MDME(IDL,1).NE.2.AND.
 100      &KFSN*MDME(IDL,1).NE.3) THEN
 101         IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1) GOTO 140
 102       ELSEIF(MDME(IDL,2).GT.100) THEN
 103         IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1) GOTO 140
 104       ELSE
 105         IDC=IDL
 106         RBR=RBR-BRAT(IDL)
 107         IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1.AND.RBR.GT.0.) GOTO 140
 108       ENDIF
 109
 110 C...Start readout of decay channel: matrix element, reset counters.
 111       MMAT=MDME(IDC,2)
 112   150 NTRY=NTRY+1
 113       IF(NTRY.GT.1000) THEN
 114          CALL LUERRM_HIJING(14
 115      $        ,'(LUDECY_HIJING:) caught in infinite loop')
 116         IF(MSTU(21).GE.1) RETURN
 117       ENDIF
 118       I=N
 119       NP=0
 120       NQ=0
 121       MBST=0
 122       IF(MMAT.GE.11.AND.MMAT.NE.46.AND.P(IP,4).GT.20.*P(IP,5)) MBST=1
 123       DO 160 J=1,4
 124       PV(1,J)=0.
 125   160 IF(MBST.EQ.0) PV(1,J)=P(IP,J)
 126       IF(MBST.EQ.1) PV(1,4)=P(IP,5)
 127       PV(1,5)=P(IP,5)
 128       PS=0.
 129       PSQ=0.
 130       MREM=0
 131
 132 C...Read out decay products. Convert to standard flavour code.
 133       JTMAX=5
 134       IF(MDME(IDC+1,2).EQ.101) JTMAX=10
 135       DO 170 JT=1,JTMAX
 136       IF(JT.LE.5) KP=KFDP(IDC,JT)
 137       IF(JT.GE.6) KP=KFDP(IDC+1,JT-5)
 138       IF(KP.EQ.0) GOTO 170
 139       KPA=IABS(KP)
 140       KCP=LUCOMP_HIJING(KPA)
 141       IF(KCHG(KCP,3).EQ.0.AND.KPA.NE.81.AND.KPA.NE.82) THEN
 142         KFP=KP
 143       ELSEIF(KPA.NE.81.AND.KPA.NE.82) THEN
 144         KFP=KFS*KP
 145       ELSEIF(KPA.EQ.81.AND.MOD(KFA/1000,10).EQ.0) THEN
 146         KFP=-KFS*MOD(KFA/10,10)
 147       ELSEIF(KPA.EQ.81.AND.MOD(KFA/100,10).GE.MOD(KFA/10,10)) THEN
 148         KFP=KFS*(100*MOD(KFA/10,100)+3)
 149       ELSEIF(KPA.EQ.81) THEN
 150         KFP=KFS*(1000*MOD(KFA/10,10)+100*MOD(KFA/100,10)+1)
 151       ELSEIF(KP.EQ.82) THEN
 152          CALL LUKFDI_HIJING(-KFS*INT(1.+(2.+PARJ(2))*RLU_HIJING(0)),0
 153      $        ,KFP,KDUMP)
 154         IF(KFP.EQ.0) GOTO 150
 155         MSTJ(93)=1
 156         IF(PV(1,5).LT.PARJ(32)+2.*ULMASS_HIJING(KFP)) GOTO 150
 157       ELSEIF(KP.EQ.-82) THEN
 158         KFP=-KFP
 159         IF(IABS(KFP).GT.10) KFP=KFP+ISIGN(10000,KFP)
 160       ENDIF
 161       IF(KPA.EQ.81.OR.KPA.EQ.82) KCP=LUCOMP_HIJING(KFP)
 162
 163 C...Add decay product to event record or to quark flavour list.
 164       KFPA=IABS(KFP)
 165       KQP=KCHG(KCP,2)
 166       IF(MMAT.GE.11.AND.MMAT.LE.30.AND.KQP.NE.0) THEN
 167         NQ=NQ+1
 168         KFLO(NQ)=KFP
 169         MSTJ(93)=2
 170         PSQ=PSQ+ULMASS_HIJING(KFLO(NQ))
 171       ELSEIF(MMAT.GE.42.AND.MMAT.LE.43.AND.NP.EQ.3.AND.MOD(NQ,2).EQ.1)
 172      &THEN
 173         NQ=NQ-1
 174         PS=PS-P(I,5)
 175         K(I,1)=1
 176         KFI=K(I,2)
 177         CALL LUKFDI_HIJING(KFP,KFI,KFLDMP,K(I,2))
 178         IF(K(I,2).EQ.0) GOTO 150
 179         MSTJ(93)=1
 180         P(I,5)=ULMASS_HIJING(K(I,2))
 181         PS=PS+P(I,5)
 182       ELSE
 183         I=I+1
 184         NP=NP+1
 185         IF(MMAT.NE.33.AND.KQP.NE.0) NQ=NQ+1
 186         IF(MMAT.EQ.33.AND.KQP.NE.0.AND.KQP.NE.2) NQ=NQ+1
 187         K(I,1)=1+MOD(NQ,2)
 188         IF(MMAT.EQ.4.AND.JT.LE.2.AND.KFP.EQ.21) K(I,1)=2
 189         IF(MMAT.EQ.4.AND.JT.EQ.3) K(I,1)=1
 190         K(I,2)=KFP
 191         K(I,3)=IP
 192         K(I,4)=0
 193         K(I,5)=0
 194         P(I,5)=ULMASS_HIJING(KFP)
 195         IF(MMAT.EQ.45.AND.KFPA.EQ.89) P(I,5)=PARJ(32)
 196         PS=PS+P(I,5)
 197       ENDIF
 198   170 CONTINUE
 199
 200 C...Choose decay multiplicity in phase space model.
 201   180 IF(MMAT.GE.11.AND.MMAT.LE.30) THEN
 202         PSP=PS
 203         CNDE=PARJ(61)*LOG(MAX((PV(1,5)-PS-PSQ)/PARJ(62),1.1))
 204         IF(MMAT.EQ.12) CNDE=CNDE+PARJ(63)
 205   190   NTRY=NTRY+1
 206         IF(NTRY.GT.1000) THEN
 207            CALL LUERRM_HIJING(14
 208      $          ,'(LUDECY_HIJING:) caught in infinite loop')
 209           IF(MSTU(21).GE.1) RETURN
 210         ENDIF
 211         IF(MMAT.LE.20) THEN
 212           GAUSS=SQRT(-2.*CNDE*LOG(MAX(1E-10,RLU_HIJING(0))))*
 213      &    SIN(PARU(2)*RLU_HIJING(0))
 214           ND=0.5+0.5*NP+0.25*NQ+CNDE+GAUSS
 215           IF(ND.LT.NP+NQ/2.OR.ND.LT.2.OR.ND.GT.10) GOTO 190
 216           IF(MMAT.EQ.13.AND.ND.EQ.2) GOTO 190
 217           IF(MMAT.EQ.14.AND.ND.LE.3) GOTO 190
 218           IF(MMAT.EQ.15.AND.ND.LE.4) GOTO 190
 219         ELSE
 220           ND=MMAT-20
 221         ENDIF
 222
 223 C...Form hadrons from flavour content.
 224         DO 200 JT=1,4
 225   200   KFL1(JT)=KFLO(JT)
 226         IF(ND.EQ.NP+NQ/2) GOTO 220
 227         DO 210 I=N+NP+1,N+ND-NQ/2
 228         JT=1+INT((NQ-1)*RLU_HIJING(0))
 229         CALL LUKFDI_HIJING(KFL1(JT),0,KFL2,K(I,2))
 230         IF(K(I,2).EQ.0) GOTO 190
 231   210   KFL1(JT)=-KFL2
 232   220   JT=2
 233         JT2=3
 234         JT3=4
 235         IF(NQ.EQ.4.AND.RLU_HIJING(0).LT.PARJ(66)) JT=4
 236         IF(JT.EQ.4.AND.ISIGN(1,KFL1(1)*(10-IABS(KFL1(1))))*
 237      &  ISIGN(1,KFL1(JT)*(10-IABS(KFL1(JT)))).GT.0) JT=3
 238         IF(JT.EQ.3) JT2=2
 239         IF(JT.EQ.4) JT3=2
 240         CALL LUKFDI_HIJING(KFL1(1),KFL1(JT),KFLDMP,K(N+ND-NQ/2+1,2))
 241         IF(K(N+ND-NQ/2+1,2).EQ.0) GOTO 190
 242         IF(NQ.EQ.4) CALL LUKFDI_HIJING(KFL1(JT2),KFL1(JT3),KFLDMP,K(N+ND
 243      $       ,2))
 244         IF(NQ.EQ.4.AND.K(N+ND,2).EQ.0) GOTO 190
 245
 246 C...Check that sum of decay product masses not too large.
 247         PS=PSP
 248         DO 230 I=N+NP+1,N+ND
 249         K(I,1)=1
 250         K(I,3)=IP
 251         K(I,4)=0
 252         K(I,5)=0
 253         P(I,5)=ULMASS_HIJING(K(I,2))
 254   230   PS=PS+P(I,5)
 255         IF(PS+PARJ(64).GT.PV(1,5)) GOTO 190
 256
 257 C...Rescale energy to subtract off spectator quark mass.
 258       ELSEIF((MMAT.EQ.31.OR.MMAT.EQ.33.OR.MMAT.EQ.44.OR.MMAT.EQ.45).
 259      &AND.NP.GE.3) THEN
 260         PS=PS-P(N+NP,5)
 261         PQT=(P(N+NP,5)+PARJ(65))/PV(1,5)
 262         DO 240 J=1,5
 263         P(N+NP,J)=PQT*PV(1,J)
 264   240   PV(1,J)=(1.-PQT)*PV(1,J)
 265         IF(PS+PARJ(64).GT.PV(1,5)) GOTO 150
 266         ND=NP-1
 267         MREM=1
 268
 269 C...Phase space factors imposed in W decay.
 270       ELSEIF(MMAT.EQ.46) THEN
 271         MSTJ(93)=1
 272         PSMC=ULMASS_HIJING(K(N+1,2))
 273         MSTJ(93)=1
 274         PSMC=PSMC+ULMASS_HIJING(K(N+2,2))
 275         IF(MAX(PS,PSMC)+PARJ(32).GT.PV(1,5)) GOTO 130
 276         HR1=(P(N+1,5)/PV(1,5))**2
 277         HR2=(P(N+2,5)/PV(1,5))**2
 278         IF((1.-HR1-HR2)*(2.+HR1+HR2)*SQRT((1.-HR1-HR2)**2-4.*HR1*HR2).
 279      &  LT.2.*RLU_HIJING(0)) GOTO 130
 280         ND=NP
 281
 282 C...Fully specified final state: check mass broadening effects.
 283       ELSE
 284         IF(NP.GE.2.AND.PS+PARJ(64).GT.PV(1,5)) GOTO 150
 285         ND=NP
 286       ENDIF
 287
 288 C...Select W mass in decay Q -> W + q, without W propagator.
 289       IF(MMAT.EQ.45.AND.MSTJ(25).LE.0) THEN
 290         HLQ=(PARJ(32)/PV(1,5))**2
 291         HUQ=(1.-(P(N+2,5)+PARJ(64))/PV(1,5))**2
 292         HRQ=(P(N+2,5)/PV(1,5))**2
 293   250   HW=HLQ+RLU_HIJING(0)*(HUQ-HLQ)
 294         IF(HMEPS(HW).LT.RLU_HIJING(0)) GOTO 250
 295         P(N+1,5)=PV(1,5)*SQRT(HW)
 296
 297 C...Ditto, including W propagator. Divide mass range into three regions.
 298       ELSEIF(MMAT.EQ.45) THEN
 299         HQW=(PV(1,5)/PMAS(24,1))**2
 300         HLW=(PARJ(32)/PMAS(24,1))**2
 301         HUW=((PV(1,5)-P(N+2,5)-PARJ(64))/PMAS(24,1))**2
 302         HRQ=(P(N+2,5)/PV(1,5))**2
 303         HG=PMAS(24,2)/PMAS(24,1)
 304         HATL=ATAN((HLW-1.)/HG)
 305         HM=MIN(1.,HUW-0.001)
 306         HMV1=HMEPS(HM/HQW)/((HM-1.)**2+HG**2)
 307   260   HM=HM-HG
 308         HMV2=HMEPS(HM/HQW)/((HM-1.)**2+HG**2)
 309         HSAV1=HMEPS(HM/HQW)
 310         HSAV2=1./((HM-1.)**2+HG**2)
 311         IF(HMV2.GT.HMV1.AND.HM-HG.GT.HLW) THEN
 312           HMV1=HMV2
 313           GOTO 260
 314         ENDIF
 315         HMV=MIN(2.*HMV1,HMEPS(HM/HQW)/HG**2)
 316         HM1=1.-SQRT(1./HMV-HG**2)
 317         IF(HM1.GT.HLW.AND.HM1.LT.HM) THEN
 318           HM=HM1
 319         ELSEIF(HMV2.LE.HMV1) THEN
 320           HM=MAX(HLW,HM-MIN(0.1,1.-HM))
 321         ENDIF
 322         HATM=ATAN((HM-1.)/HG)
 323         HWT1=(HATM-HATL)/HG
 324         HWT2=HMV*(MIN(1.,HUW)-HM)
 325         HWT3=0.
 326         IF(HUW.GT.1.) THEN
 327           HATU=ATAN((HUW-1.)/HG)
 328           HMP1=HMEPS(1./HQW)
 329           HWT3=HMP1*HATU/HG
 330         ENDIF
 331
 332 C...Select mass region and W mass there. Accept according to weight.
 333   270   HREG=RLU_HIJING(0)*(HWT1+HWT2+HWT3)
 334         IF(HREG.LE.HWT1) THEN
 335           HW=1.+HG*TAN(HATL+RLU_HIJING(0)*(HATM-HATL))
 336           HACC=HMEPS(HW/HQW)
 337         ELSEIF(HREG.LE.HWT1+HWT2) THEN
 338           HW=HM+RLU_HIJING(0)*(MIN(1.,HUW)-HM)
 339           HACC=HMEPS(HW/HQW)/((HW-1.)**2+HG**2)/HMV
 340         ELSE
 341           HW=1.+HG*TAN(RLU_HIJING(0)*HATU)
 342           HACC=HMEPS(HW/HQW)/HMP1
 343         ENDIF
 344         IF(HACC.LT.RLU_HIJING(0)) GOTO 270
 345         P(N+1,5)=PMAS(24,1)*SQRT(HW)
 346       ENDIF
 347
 348 C...Determine position of grandmother, number of sisters, Q -> W sign.
 349       NM=0
 350       MSGN=0
 351       IF(MMAT.EQ.3.OR.MMAT.EQ.46) THEN
 352         IM=K(IP,3)
 353         IF(IM.LT.0.OR.IM.GE.IP) IM=0
 354         IF(IM.NE.0) KFAM=IABS(K(IM,2))
 355         IF(IM.NE.0.AND.MMAT.EQ.3) THEN
 356           DO 280 IL=MAX(IP-2,IM+1),MIN(IP+2,N)
 357   280     IF(K(IL,3).EQ.IM) NM=NM+1
 358           IF(NM.NE.2.OR.KFAM.LE.100.OR.MOD(KFAM,10).NE.1.OR.
 359      &    MOD(KFAM/1000,10).NE.0) NM=0
 360         ELSEIF(IM.NE.0.AND.MMAT.EQ.46) THEN
 361           MSGN=ISIGN(1,K(IM,2)*K(IP,2))
 362           IF(KFAM.GT.100.AND.MOD(KFAM/1000,10).EQ.0) MSGN=
 363      &    MSGN*(-1)**MOD(KFAM/100,10)
 364         ENDIF
 365       ENDIF
 366
 367 C...Kinematics of one-particle decays.
 368       IF(ND.EQ.1) THEN
 369         DO 290 J=1,4
 370   290   P(N+1,J)=P(IP,J)
 371         GOTO 510
 372       ENDIF
 373
 374 C...Calculate maximum weight ND-particle decay.
 375       PV(ND,5)=P(N+ND,5)
 376       IF(ND.GE.3) THEN
 377         WTMAX=1./WTCOR(ND-2)
 378         PMAX=PV(1,5)-PS+P(N+ND,5)
 379         PMIN=0.
 380         DO 300 IL=ND-1,1,-1
 381         PMAX=PMAX+P(N+IL,5)
 382         PMIN=PMIN+P(N+IL+1,5)
 383   300   WTMAX=WTMAX*PAWT(PMAX,PMIN,P(N+IL,5))
 384       ENDIF
 385
 386 C...Find virtual gamma mass in Dalitz decay.
 387   310 IF(ND.EQ.2) THEN
 388       ELSEIF(MMAT.EQ.2) THEN
 389         PMES=4.*PMAS(11,1)**2
 390         PMRHO2=PMAS(131,1)**2
 391         PGRHO2=PMAS(131,2)**2
 392   320   PMST=PMES*(P(IP,5)**2/PMES)**RLU_HIJING(0)
 393         WT=(1+0.5*PMES/PMST)*SQRT(MAX(0.,1.-PMES/PMST))*
 394      &  (1.-PMST/P(IP,5)**2)**3*(1.+PGRHO2/PMRHO2)/
 395      &  ((1.-PMST/PMRHO2)**2+PGRHO2/PMRHO2)
 396         IF(WT.LT.RLU_HIJING(0)) GOTO 320
 397         PV(2,5)=MAX(2.00001*PMAS(11,1),SQRT(PMST))
 398
 399 C...M-generator gives weight. If rejected, try again.
 400       ELSE
 401   330   RORD(1)=1.
 402         DO 350 IL1=2,ND-1
 403         RSAV=RLU_HIJING(0)
 404         DO 340 IL2=IL1-1,1,-1
 405         IF(RSAV.LE.RORD(IL2)) GOTO 350
 406   340   RORD(IL2+1)=RORD(IL2)
 407   350   RORD(IL2+1)=RSAV
 408         RORD(ND)=0.
 409         WT=1.
 410         DO 360 IL=ND-1,1,-1
 411         PV(IL,5)=PV(IL+1,5)+P(N+IL,5)+(RORD(IL)-RORD(IL+1))*(PV(1,5)-PS)
 412   360   WT=WT*PAWT(PV(IL,5),PV(IL+1,5),P(N+IL,5))
 413         IF(WT.LT.RLU_HIJING(0)*WTMAX) GOTO 330
 414       ENDIF
 415
 416 C...Perform two-particle decays in respective CM frame.
 417   370 DO 390 IL=1,ND-1
 418       PA=PAWT(PV(IL,5),PV(IL+1,5),P(N+IL,5))
 419       UE(3)=2.*RLU_HIJING(0)-1.
 420       PHI=PARU(2)*RLU_HIJING(0)
 421       UE(1)=SQRT(1.-UE(3)**2)*COS(PHI)
 422       UE(2)=SQRT(1.-UE(3)**2)*SIN(PHI)
 423       DO 380 J=1,3
 424       P(N+IL,J)=PA*UE(J)
 425   380 PV(IL+1,J)=-PA*UE(J)
 426       P(N+IL,4)=SQRT(PA**2+P(N+IL,5)**2)
 427   390 PV(IL+1,4)=SQRT(PA**2+PV(IL+1,5)**2)
 428
 429 C...Lorentz transform decay products to lab frame.
 430       DO 400 J=1,4
 431   400 P(N+ND,J)=PV(ND,J)
 432       DO 430 IL=ND-1,1,-1
 433       DO 410 J=1,3
 434   410 BE(J)=PV(IL,J)/PV(IL,4)
 435       GA=PV(IL,4)/PV(IL,5)
 436       DO 430 I=N+IL,N+ND
 437       BEP=BE(1)*P(I,1)+BE(2)*P(I,2)+BE(3)*P(I,3)
 438       DO 420 J=1,3
 439   420 P(I,J)=P(I,J)+GA*(GA*BEP/(1.+GA)+P(I,4))*BE(J)
 440   430 P(I,4)=GA*(P(I,4)+BEP)
 441
 442 C...Matrix elements for omega and phi decays.
 443       IF(MMAT.EQ.1) THEN
 444         WT=(P(N+1,5)*P(N+2,5)*P(N+3,5))**2-(P(N+1,5)*FOUR(N+2,N+3))**2
 445      &  -(P(N+2,5)*FOUR(N+1,N+3))**2-(P(N+3,5)*FOUR(N+1,N+2))**2
 446      &  +2.*FOUR(N+1,N+2)*FOUR(N+1,N+3)*FOUR(N+2,N+3)
 447         IF(MAX(WT*WTCOR(9)/P(IP,5)**6,0.001).LT.RLU_HIJING(0)) GOTO 310
 448
 449 C...Matrix elements for pi0 or eta Dalitz decay to gamma e+ e-.
 450       ELSEIF(MMAT.EQ.2) THEN
 451         FOUR12=FOUR(N+1,N+2)
 452         FOUR13=FOUR(N+1,N+3)
 453         FOUR23=0.5*PMST-0.25*PMES
 454         WT=(PMST-0.5*PMES)*(FOUR12**2+FOUR13**2)+
 455      &  PMES*(FOUR12*FOUR13+FOUR12**2+FOUR13**2)
 456         IF(WT.LT.RLU_HIJING(0)*0.25*PMST*(P(IP,5)**2-PMST)**2) GOTO 370
 457
 458 C...Matrix element for S0 -> S1 + V1 -> S1 + S2 + S3 (S scalar,
 459 C...V vector), of form cos**2(theta02) in V1 rest frame.
 460       ELSEIF(MMAT.EQ.3.AND.NM.EQ.2) THEN
 461         IF((P(IP,5)**2*FOUR(IM,N+1)-FOUR(IP,IM)*FOUR(IP,N+1))**2.LE.
 462      &        RLU_HIJING(0)*(FOUR(IP,IM)**2-(P(IP,5)*P(IM,5))**2)
 463      $        *(FOUR(IP,N+1)**2-(P(IP,5)*P(N+1,5))**2)) GOTO 370
 464
 465 C...Matrix element for "onium" -> g + g + g or gamma + g + g.
 466       ELSEIF(MMAT.EQ.4) THEN
 467         HX1=2.*FOUR(IP,N+1)/P(IP,5)**2
 468         HX2=2.*FOUR(IP,N+2)/P(IP,5)**2
 469         HX3=2.*FOUR(IP,N+3)/P(IP,5)**2
 470         WT=((1.-HX1)/(HX2*HX3))**2+((1.-HX2)/(HX1*HX3))**2+
 471      &  ((1.-HX3)/(HX1*HX2))**2
 472         IF(WT.LT.2.*RLU_HIJING(0)) GOTO 310
 473         IF(K(IP+1,2).EQ.22.AND.(1.-HX1)*P(IP,5)**2.LT.4.*PARJ(32)**2)
 474      &  GOTO 310
 475
 476 C...Effective matrix element for nu spectrum in tau -> nu + hadrons.
 477       ELSEIF(MMAT.EQ.41) THEN
 478         HX1=2.*FOUR(IP,N+1)/P(IP,5)**2
 479         IF(8.*HX1*(3.-2.*HX1)/9..LT.RLU_HIJING(0)) GOTO 310
 480
 481 C...Matrix elements for weak decays (only semileptonic for c and b)
 482       ELSEIF(MMAT.GE.42.AND.MMAT.LE.44.AND.ND.EQ.3) THEN
 483         IF(MBST.EQ.0) WT=FOUR(IP,N+1)*FOUR(N+2,N+3)
 484         IF(MBST.EQ.1) WT=P(IP,5)*P(N+1,4)*FOUR(N+2,N+3)
 485         IF(WT.LT.RLU_HIJING(0)*P(IP,5)*PV(1,5)**3/WTCOR(10)) GOTO 310
 486       ELSEIF(MMAT.GE.42.AND.MMAT.LE.44) THEN
 487         DO 440 J=1,4
 488         P(N+NP+1,J)=0.
 489         DO 440 IS=N+3,N+NP
 490   440   P(N+NP+1,J)=P(N+NP+1,J)+P(IS,J)
 491         IF(MBST.EQ.0) WT=FOUR(IP,N+1)*FOUR(N+2,N+NP+1)
 492         IF(MBST.EQ.1) WT=P(IP,5)*P(N+1,4)*FOUR(N+2,N+NP+1)
 493         IF(WT.LT.RLU_HIJING(0)*P(IP,5)*PV(1,5)**3/WTCOR(10)) GOTO 310
 494
 495 C...Angular distribution in W decay.
 496       ELSEIF(MMAT.EQ.46.AND.MSGN.NE.0) THEN
 497         IF(MSGN.GT.0) WT=FOUR(IM,N+1)*FOUR(N+2,IP+1)
 498         IF(MSGN.LT.0) WT=FOUR(IM,N+2)*FOUR(N+1,IP+1)
 499         IF(WT.LT.RLU_HIJING(0)*P(IM,5)**4/WTCOR(10)) GOTO 370
 500       ENDIF
 501
 502 C...Scale back energy and reattach spectator.
 503       IF(MREM.EQ.1) THEN
 504         DO 450 J=1,5
 505   450   PV(1,J)=PV(1,J)/(1.-PQT)
 506         ND=ND+1
 507         MREM=0
 508       ENDIF
 509
 510 C...Low invariant mass for system with spectator quark gives particle,
 511 C...not two jets. Readjust momenta accordingly.
 512       IF((MMAT.EQ.31.OR.MMAT.EQ.45).AND.ND.EQ.3) THEN
 513         MSTJ(93)=1
 514         PM2=ULMASS_HIJING(K(N+2,2))
 515         MSTJ(93)=1
 516         PM3=ULMASS_HIJING(K(N+3,2))
 517         IF(P(N+2,5)**2+P(N+3,5)**2+2.*FOUR(N+2,N+3).GE.
 518      &  (PARJ(32)+PM2+PM3)**2) GOTO 510
 519         K(N+2,1)=1
 520         KFTEMP=K(N+2,2)
 521         CALL LUKFDI_HIJING(KFTEMP,K(N+3,2),KFLDMP,K(N+2,2))
 522         IF(K(N+2,2).EQ.0) GOTO 150
 523         P(N+2,5)=ULMASS_HIJING(K(N+2,2))
 524         PS=P(N+1,5)+P(N+2,5)
 525         PV(2,5)=P(N+2,5)
 526         MMAT=0
 527         ND=2
 528         GOTO 370
 529       ELSEIF(MMAT.EQ.44) THEN
 530         MSTJ(93)=1
 531         PM3=ULMASS_HIJING(K(N+3,2))
 532         MSTJ(93)=1
 533         PM4=ULMASS_HIJING(K(N+4,2))
 534         IF(P(N+3,5)**2+P(N+4,5)**2+2.*FOUR(N+3,N+4).GE.
 535      &  (PARJ(32)+PM3+PM4)**2) GOTO 480
 536         K(N+3,1)=1
 537         KFTEMP=K(N+3,2)
 538         CALL LUKFDI_HIJING(KFTEMP,K(N+4,2),KFLDMP,K(N+3,2))
 539         IF(K(N+3,2).EQ.0) GOTO 150
 540         P(N+3,5)=ULMASS_HIJING(K(N+3,2))
 541         DO 460 J=1,3
 542   460   P(N+3,J)=P(N+3,J)+P(N+4,J)
 543         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)
 544         HA=P(N+1,4)**2-P(N+2,4)**2
 545         HB=HA-(P(N+1,5)**2-P(N+2,5)**2)
 546         HC=(P(N+1,1)-P(N+2,1))**2+(P(N+1,2)-P(N+2,2))**2+
 547      &  (P(N+1,3)-P(N+2,3))**2
 548         HD=(PV(1,4)-P(N+3,4))**2
 549         HE=HA**2-2.*HD*(P(N+1,4)**2+P(N+2,4)**2)+HD**2
 550         HF=HD*HC-HB**2
 551         HG=HD*HC-HA*HB
 552         HH=(SQRT(HG**2+HE*HF)-HG)/(2.*HF)
 553         DO 470 J=1,3
 554         PCOR=HH*(P(N+1,J)-P(N+2,J))
 555         P(N+1,J)=P(N+1,J)+PCOR
 556   470   P(N+2,J)=P(N+2,J)-PCOR
 557         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)
 558         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)
 559         ND=ND-1
 560       ENDIF
 561
 562 C...Check invariant mass of W jets. May give one particle or start over.
 563   480 IF(MMAT.GE.42.AND.MMAT.LE.44.AND.IABS(K(N+1,2)).LT.10) THEN
 564         PMR=SQRT(MAX(0.,P(N+1,5)**2+P(N+2,5)**2+2.*FOUR(N+1,N+2)))
 565         MSTJ(93)=1
 566         PM1=ULMASS_HIJING(K(N+1,2))
 567         MSTJ(93)=1
 568         PM2=ULMASS_HIJING(K(N+2,2))
 569         IF(PMR.GT.PARJ(32)+PM1+PM2) GOTO 490
 570         KFLDUM=INT(1.5+RLU_HIJING(0))
 571         CALL LUKFDI_HIJING(K(N+1,2),-ISIGN(KFLDUM,K(N+1,2)),KFLDMP,KF1)
 572         CALL LUKFDI_HIJING(K(N+2,2),-ISIGN(KFLDUM,K(N+2,2)),KFLDMP,KF2)
 573         IF(KF1.EQ.0.OR.KF2.EQ.0) GOTO 150
 574         PSM=ULMASS_HIJING(KF1)+ULMASS_HIJING(KF2)
 575         IF(MMAT.EQ.42.AND.PMR.GT.PARJ(64)+PSM) GOTO 490
 576         IF(MMAT.GE.43.AND.PMR.GT.0.2*PARJ(32)+PSM) GOTO 490
 577         IF(ND.EQ.4.OR.KFA.EQ.15) GOTO 150
 578         K(N+1,1)=1
 579         KFTEMP=K(N+1,2)
 580         CALL LUKFDI_HIJING(KFTEMP,K(N+2,2),KFLDMP,K(N+1,2))
 581         IF(K(N+1,2).EQ.0) GOTO 150
 582         P(N+1,5)=ULMASS_HIJING(K(N+1,2))
 583         K(N+2,2)=K(N+3,2)
 584         P(N+2,5)=P(N+3,5)
 585         PS=P(N+1,5)+P(N+2,5)
 586         PV(2,5)=P(N+3,5)
 587         MMAT=0
 588         ND=2
 589         GOTO 370
 590       ENDIF
 591
 592 C...Phase space decay of partons from W decay.
 593   490 IF(MMAT.EQ.42.AND.IABS(K(N+1,2)).LT.10) THEN
 594         KFLO(1)=K(N+1,2)
 595         KFLO(2)=K(N+2,2)
 596         K(N+1,1)=K(N+3,1)
 597         K(N+1,2)=K(N+3,2)
 598         DO 500 J=1,5
 599         PV(1,J)=P(N+1,J)+P(N+2,J)
 600   500   P(N+1,J)=P(N+3,J)
 601         PV(1,5)=PMR
 602         N=N+1
 603         NP=0
 604         NQ=2
 605         PS=0.
 606         MSTJ(93)=2
 607         PSQ=ULMASS_HIJING(KFLO(1))
 608         MSTJ(93)=2
 609         PSQ=PSQ+ULMASS_HIJING(KFLO(2))
 610         MMAT=11
 611         GOTO 180
 612       ENDIF
 613
 614 C...Boost back for rapidly moving particle.
 615   510 N=N+ND
 616       IF(MBST.EQ.1) THEN
 617         DO 520 J=1,3
 618   520   BE(J)=P(IP,J)/P(IP,4)
 619         GA=P(IP,4)/P(IP,5)
 620         DO 540 I=NSAV+1,N
 621         BEP=BE(1)*P(I,1)+BE(2)*P(I,2)+BE(3)*P(I,3)
 622         DO 530 J=1,3
 623   530   P(I,J)=P(I,J)+GA*(GA*BEP/(1.+GA)+P(I,4))*BE(J)
 624   540   P(I,4)=GA*(P(I,4)+BEP)
 625       ENDIF
 626
 627 C...Fill in position of decay vertex.
 628       DO 560 I=NSAV+1,N
 629       DO 550 J=1,4
 630   550 V(I,J)=VDCY(J)
 631   560 V(I,5)=0.
 632
 633 C...Set up for parton shower evolution from jets.
 634       IF(MSTJ(23).GE.1.AND.MMAT.EQ.4.AND.K(NSAV+1,2).EQ.21) THEN
 635         K(NSAV+1,1)=3
 636         K(NSAV+2,1)=3
 637         K(NSAV+3,1)=3
 638         K(NSAV+1,4)=MSTU(5)*(NSAV+2)
 639         K(NSAV+1,5)=MSTU(5)*(NSAV+3)
 640         K(NSAV+2,4)=MSTU(5)*(NSAV+3)
 641         K(NSAV+2,5)=MSTU(5)*(NSAV+1)
 642         K(NSAV+3,4)=MSTU(5)*(NSAV+1)
 643         K(NSAV+3,5)=MSTU(5)*(NSAV+2)
 644         MSTJ(92)=-(NSAV+1)
 645       ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.4) THEN
 646         K(NSAV+2,1)=3
 647         K(NSAV+3,1)=3
 648         K(NSAV+2,4)=MSTU(5)*(NSAV+3)
 649         K(NSAV+2,5)=MSTU(5)*(NSAV+3)
 650         K(NSAV+3,4)=MSTU(5)*(NSAV+2)
 651         K(NSAV+3,5)=MSTU(5)*(NSAV+2)
 652         MSTJ(92)=NSAV+2
 653       ELSEIF(MSTJ(23).GE.1.AND.(MMAT.EQ.32.OR.MMAT.EQ.44.OR.MMAT.EQ.46).
 654      &AND.IABS(K(NSAV+1,2)).LE.10.AND.IABS(K(NSAV+2,2)).LE.10) THEN
 655         K(NSAV+1,1)=3
 656         K(NSAV+2,1)=3
 657         K(NSAV+1,4)=MSTU(5)*(NSAV+2)
 658         K(NSAV+1,5)=MSTU(5)*(NSAV+2)
 659         K(NSAV+2,4)=MSTU(5)*(NSAV+1)
 660         K(NSAV+2,5)=MSTU(5)*(NSAV+1)
 661         MSTJ(92)=NSAV+1
 662       ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.33.AND.IABS(K(NSAV+2,2)).EQ.21)
 663      &THEN
 664         K(NSAV+1,1)=3
 665         K(NSAV+2,1)=3
 666         K(NSAV+3,1)=3
 667         KCP=LUCOMP_HIJING(K(NSAV+1,2))
 668         KQP=KCHG(KCP,2)*ISIGN(1,K(NSAV+1,2))
 669         JCON=4
 670         IF(KQP.LT.0) JCON=5
 671         K(NSAV+1,JCON)=MSTU(5)*(NSAV+2)
 672         K(NSAV+2,9-JCON)=MSTU(5)*(NSAV+1)
 673         K(NSAV+2,JCON)=MSTU(5)*(NSAV+3)
 674         K(NSAV+3,9-JCON)=MSTU(5)*(NSAV+2)
 675         MSTJ(92)=NSAV+1
 676       ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.33) THEN
 677         K(NSAV+1,1)=3
 678         K(NSAV+3,1)=3
 679         K(NSAV+1,4)=MSTU(5)*(NSAV+3)
 680         K(NSAV+1,5)=MSTU(5)*(NSAV+3)
 681         K(NSAV+3,4)=MSTU(5)*(NSAV+1)
 682         K(NSAV+3,5)=MSTU(5)*(NSAV+1)
 683         MSTJ(92)=NSAV+1
 684       ENDIF
 685
 686 C...Mark decayed particle.
 687       IF(K(IP,1).EQ.5) K(IP,1)=15
 688       IF(K(IP,1).LE.10) K(IP,1)=11
 689       K(IP,4)=NSAV+1
 690       K(IP,5)=N
 691
 692       RETURN
 693       END