HIJING/hipyset1_35/ludecy_hijing.F

   1 * $Id$
   2
   3 C*********************************************************************
   4
   5       FUNCTION PAWT(A,B,C)
   6       IF(((A**2-(B+C)**2)*(A**2-(B-C)**2)).GT.0) THEN
   7          PAWT = SQRT((A**2-(B+C)**2)*(A**2-(B-C)**2))/(2.*A)
   8       ELSE
   9          PAWT = 0
  10       ENDIF
  11       RETURN
  12       END
  13
  14       SUBROUTINE LUDECY_HIJING(IP)
  15
  16 C...Purpose: to handle the decay of unstable particles.
  17 #include "lujets_hijing.inc"
  18 #include "ludat1_hijing.inc"
  19 #include "ludat2_hijing.inc"
  20 #include "ludat3_hijing.inc"
  21       DIMENSION VDCY(4),KFLO(4),KFL1(4),PV(10,5),RORD(10),UE(3),BE(3),
  22      &WTCOR(10)
  23       DATA WTCOR/2.,5.,15.,60.,250.,1500.,1.2E4,1.2E5,150.,16./
  24
  25 C...Functions: momentum in two-particle decays, four-product and
  26 C...matrix element times phase space in weak decays.
  27
  28       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)
  29       HMEPS(HA)=((1.-HRQ-HA)**2+3.*HA*(1.+HRQ-HA))*
  30      &SQRT((1.-HRQ-HA)**2-4.*HRQ*HA)
  31
  32 C...Initial values.
  33       NTRY=0
  34       NSAV=N
  35       KFA=IABS(K(IP,2))
  36       KFS=ISIGN(1,K(IP,2))
  37       KC=LUCOMP_HIJING(KFA)
  38       MSTJ(92)=0
  39
  40 C...Choose lifetime and determine decay vertex.
  41       IF(K(IP,1).EQ.5) THEN
  42         V(IP,5)=0.
  43       ELSEIF(K(IP,1).NE.4) THEN
  44         V(IP,5)=-PMAS(KC,4)*LOG(RLU_HIJING(0))
  45       ENDIF
  46       DO 100 J=1,4
  47   100 VDCY(J)=V(IP,J)+V(IP,5)*P(IP,J)/P(IP,5)
  48
  49 C...Determine whether decay allowed or not.
  50       MOUT=0
  51       IF(MSTJ(22).EQ.2) THEN
  52         IF(PMAS(KC,4).GT.PARJ(71)) MOUT=1
  53       ELSEIF(MSTJ(22).EQ.3) THEN
  54         IF(VDCY(1)**2+VDCY(2)**2+VDCY(3)**2.GT.PARJ(72)**2) MOUT=1
  55       ELSEIF(MSTJ(22).EQ.4) THEN
  56         IF(VDCY(1)**2+VDCY(2)**2.GT.PARJ(73)**2) MOUT=1
  57         IF(ABS(VDCY(3)).GT.PARJ(74)) MOUT=1
  58       ENDIF
  59       IF(MOUT.EQ.1.AND.K(IP,1).NE.5) THEN
  60         K(IP,1)=4
  61         RETURN
  62       ENDIF
  63
  64 C...Check existence of decay channels. Particle/antiparticle rules.
  65       KCA=KC
  66       IF(MDCY(KC,2).GT.0) THEN
  67         MDMDCY=MDME(MDCY(KC,2),2)
  68         IF(MDMDCY.GT.80.AND.MDMDCY.LE.90) KCA=MDMDCY
  69       ENDIF
  70       IF(MDCY(KCA,2).LE.0.OR.MDCY(KCA,3).LE.0) THEN
  71          CALL LUERRM_HIJING(9
  72      $        ,'(LUDECY_HIJING:) no decay channel defined')
  73         RETURN
  74       ENDIF
  75       IF(MOD(KFA/1000,10).EQ.0.AND.(KCA.EQ.85.OR.KCA.EQ.87)) KFS=-KFS
  76       IF(KCHG(KC,3).EQ.0) THEN
  77         KFSP=1
  78         KFSN=0
  79         IF(RLU_HIJING(0).GT.0.5) KFS=-KFS
  80       ELSEIF(KFS.GT.0) THEN
  81         KFSP=1
  82         KFSN=0
  83       ELSE
  84         KFSP=0
  85         KFSN=1
  86       ENDIF
  87
  88 C...Sum branching ratios of allowed decay channels.
  89   110 NOPE=0
  90       BRSU=0.
  91       DO 120 IDL=MDCY(KCA,2),MDCY(KCA,2)+MDCY(KCA,3)-1
  92       IF(MDME(IDL,1).NE.1.AND.KFSP*MDME(IDL,1).NE.2.AND.
  93      &KFSN*MDME(IDL,1).NE.3) GOTO 120
  94       IF(MDME(IDL,2).GT.100) GOTO 120
  95       NOPE=NOPE+1
  96       BRSU=BRSU+BRAT(IDL)
  97   120 CONTINUE
  98       IF(NOPE.EQ.0) THEN
  99          CALL LUERRM_HIJING(2
 100      $        ,'(LUDECY_HIJING:) all decay channels closed by user')
 101         RETURN
 102       ENDIF
 103
 104 C...Select decay channel among allowed ones.
 105   130 RBR=BRSU*RLU_HIJING(0)
 106       IDL=MDCY(KCA,2)-1
 107   140 IDL=IDL+1
 108       IF(MDME(IDL,1).NE.1.AND.KFSP*MDME(IDL,1).NE.2.AND.
 109      &KFSN*MDME(IDL,1).NE.3) THEN
 110         IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1) GOTO 140
 111       ELSEIF(MDME(IDL,2).GT.100) THEN
 112         IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1) GOTO 140
 113       ELSE
 114         IDC=IDL
 115         RBR=RBR-BRAT(IDL)
 116         IF(IDL.LT.MDCY(KCA,2)+MDCY(KCA,3)-1.AND.RBR.GT.0.) GOTO 140
 117       ENDIF
 118
 119 C...Start readout of decay channel: matrix element, reset counters.
 120       MMAT=MDME(IDC,2)
 121   150 NTRY=NTRY+1
 122       IF(NTRY.GT.1000) THEN
 123          CALL LUERRM_HIJING(14
 124      $        ,'(LUDECY_HIJING:) caught in infinite loop')
 125         IF(MSTU(21).GE.1) RETURN
 126       ENDIF
 127       I=N
 128       NP=0
 129       NQ=0
 130       MBST=0
 131       IF(MMAT.GE.11.AND.MMAT.NE.46.AND.P(IP,4).GT.20.*P(IP,5)) MBST=1
 132       DO 160 J=1,4
 133       PV(1,J)=0.
 134   160 IF(MBST.EQ.0) PV(1,J)=P(IP,J)
 135       IF(MBST.EQ.1) PV(1,4)=P(IP,5)
 136       PV(1,5)=P(IP,5)
 137       PS=0.
 138       PSQ=0.
 139       MREM=0
 140
 141 C...Read out decay products. Convert to standard flavour code.
 142       JTMAX=5
 143       IF(MDME(IDC+1,2).EQ.101) JTMAX=10
 144       DO 170 JT=1,JTMAX
 145       IF(JT.LE.5) KP=KFDP(IDC,JT)
 146       IF(JT.GE.6) KP=KFDP(IDC+1,JT-5)
 147       IF(KP.EQ.0) GOTO 170
 148       KPA=IABS(KP)
 149       KCP=LUCOMP_HIJING(KPA)
 150       IF(KCHG(KCP,3).EQ.0.AND.KPA.NE.81.AND.KPA.NE.82) THEN
 151         KFP=KP
 152       ELSEIF(KPA.NE.81.AND.KPA.NE.82) THEN
 153         KFP=KFS*KP
 154       ELSEIF(KPA.EQ.81.AND.MOD(KFA/1000,10).EQ.0) THEN
 155         KFP=-KFS*MOD(KFA/10,10)
 156       ELSEIF(KPA.EQ.81.AND.MOD(KFA/100,10).GE.MOD(KFA/10,10)) THEN
 157         KFP=KFS*(100*MOD(KFA/10,100)+3)
 158       ELSEIF(KPA.EQ.81) THEN
 159         KFP=KFS*(1000*MOD(KFA/10,10)+100*MOD(KFA/100,10)+1)
 160       ELSEIF(KP.EQ.82) THEN
 161          CALL LUKFDI_HIJING(-KFS*INT(1.+(2.+PARJ(2))*RLU_HIJING(0)),0
 162      $        ,KFP,KDUMP)
 163         IF(KFP.EQ.0) GOTO 150
 164         MSTJ(93)=1
 165         IF(PV(1,5).LT.PARJ(32)+2.*ULMASS_HIJING(KFP)) GOTO 150
 166       ELSEIF(KP.EQ.-82) THEN
 167         KFP=-KFP
 168         IF(IABS(KFP).GT.10) KFP=KFP+ISIGN(10000,KFP)
 169       ENDIF
 170       IF(KPA.EQ.81.OR.KPA.EQ.82) KCP=LUCOMP_HIJING(KFP)
 171
 172 C...Add decay product to event record or to quark flavour list.
 173       KFPA=IABS(KFP)
 174       KQP=KCHG(KCP,2)
 175       IF(MMAT.GE.11.AND.MMAT.LE.30.AND.KQP.NE.0) THEN
 176         NQ=NQ+1
 177         KFLO(NQ)=KFP
 178         MSTJ(93)=2
 179         PSQ=PSQ+ULMASS_HIJING(KFLO(NQ))
 180       ELSEIF(MMAT.GE.42.AND.MMAT.LE.43.AND.NP.EQ.3.AND.MOD(NQ,2).EQ.1)
 181      &THEN
 182         NQ=NQ-1
 183         PS=PS-P(I,5)
 184         K(I,1)=1
 185         KFI=K(I,2)
 186         CALL LUKFDI_HIJING(KFP,KFI,KFLDMP,K(I,2))
 187         IF(K(I,2).EQ.0) GOTO 150
 188         MSTJ(93)=1
 189         P(I,5)=ULMASS_HIJING(K(I,2))
 190         PS=PS+P(I,5)
 191       ELSE
 192         I=I+1
 193         NP=NP+1
 194         IF(MMAT.NE.33.AND.KQP.NE.0) NQ=NQ+1
 195         IF(MMAT.EQ.33.AND.KQP.NE.0.AND.KQP.NE.2) NQ=NQ+1
 196         K(I,1)=1+MOD(NQ,2)
 197         IF(MMAT.EQ.4.AND.JT.LE.2.AND.KFP.EQ.21) K(I,1)=2
 198         IF(MMAT.EQ.4.AND.JT.EQ.3) K(I,1)=1
 199         K(I,2)=KFP
 200         K(I,3)=IP
 201         K(I,4)=0
 202         K(I,5)=0
 203         P(I,5)=ULMASS_HIJING(KFP)
 204         IF(MMAT.EQ.45.AND.KFPA.EQ.89) P(I,5)=PARJ(32)
 205         PS=PS+P(I,5)
 206       ENDIF
 207   170 CONTINUE
 208
 209 C...Choose decay multiplicity in phase space model.
 210   180 IF(MMAT.GE.11.AND.MMAT.LE.30) THEN
 211         PSP=PS
 212         CNDE=PARJ(61)*LOG(MAX((PV(1,5)-PS-PSQ)/PARJ(62),1.1))
 213         IF(MMAT.EQ.12) CNDE=CNDE+PARJ(63)
 214   190   NTRY=NTRY+1
 215         IF(NTRY.GT.1000) THEN
 216            CALL LUERRM_HIJING(14
 217      $          ,'(LUDECY_HIJING:) caught in infinite loop')
 218           IF(MSTU(21).GE.1) RETURN
 219         ENDIF
 220         IF(MMAT.LE.20) THEN
 221           GAUSS=SQRT(-2.*CNDE*LOG(MAX(1E-10,RLU_HIJING(0))))*
 222      &    SIN(PARU(2)*RLU_HIJING(0))
 223           ND=0.5+0.5*NP+0.25*NQ+CNDE+GAUSS
 224           IF(ND.LT.NP+NQ/2.OR.ND.LT.2.OR.ND.GT.10) GOTO 190
 225           IF(MMAT.EQ.13.AND.ND.EQ.2) GOTO 190
 226           IF(MMAT.EQ.14.AND.ND.LE.3) GOTO 190
 227           IF(MMAT.EQ.15.AND.ND.LE.4) GOTO 190
 228         ELSE
 229           ND=MMAT-20
 230         ENDIF
 231
 232 C...Form hadrons from flavour content.
 233         DO 200 JT=1,4
 234   200   KFL1(JT)=KFLO(JT)
 235         IF(ND.EQ.NP+NQ/2) GOTO 220
 236         DO 210 I=N+NP+1,N+ND-NQ/2
 237         JT=1+INT((NQ-1)*RLU_HIJING(0))
 238         CALL LUKFDI_HIJING(KFL1(JT),0,KFL2,K(I,2))
 239         IF(K(I,2).EQ.0) GOTO 190
 240   210   KFL1(JT)=-KFL2
 241   220   JT=2
 242         JT2=3
 243         JT3=4
 244         IF(NQ.EQ.4.AND.RLU_HIJING(0).LT.PARJ(66)) JT=4
 245         IF(JT.EQ.4.AND.ISIGN(1,KFL1(1)*(10-IABS(KFL1(1))))*
 246      &  ISIGN(1,KFL1(JT)*(10-IABS(KFL1(JT)))).GT.0) JT=3
 247         IF(JT.EQ.3) JT2=2
 248         IF(JT.EQ.4) JT3=2
 249         CALL LUKFDI_HIJING(KFL1(1),KFL1(JT),KFLDMP,K(N+ND-NQ/2+1,2))
 250         IF(K(N+ND-NQ/2+1,2).EQ.0) GOTO 190
 251         IF(NQ.EQ.4) CALL LUKFDI_HIJING(KFL1(JT2),KFL1(JT3),KFLDMP,K(N+ND
 252      $       ,2))
 253         IF(NQ.EQ.4.AND.K(N+ND,2).EQ.0) GOTO 190
 254
 255 C...Check that sum of decay product masses not too large.
 256         PS=PSP
 257         DO 230 I=N+NP+1,N+ND
 258         K(I,1)=1
 259         K(I,3)=IP
 260         K(I,4)=0
 261         K(I,5)=0
 262         P(I,5)=ULMASS_HIJING(K(I,2))
 263   230   PS=PS+P(I,5)
 264         IF(PS+PARJ(64).GT.PV(1,5)) GOTO 190
 265
 266 C...Rescale energy to subtract off spectator quark mass.
 267       ELSEIF((MMAT.EQ.31.OR.MMAT.EQ.33.OR.MMAT.EQ.44.OR.MMAT.EQ.45).
 268      &AND.NP.GE.3) THEN
 269         PS=PS-P(N+NP,5)
 270         PQT=(P(N+NP,5)+PARJ(65))/PV(1,5)
 271         DO 240 J=1,5
 272         P(N+NP,J)=PQT*PV(1,J)
 273   240   PV(1,J)=(1.-PQT)*PV(1,J)
 274         IF(PS+PARJ(64).GT.PV(1,5)) GOTO 150
 275         ND=NP-1
 276         MREM=1
 277
 278 C...Phase space factors imposed in W decay.
 279       ELSEIF(MMAT.EQ.46) THEN
 280         MSTJ(93)=1
 281         PSMC=ULMASS_HIJING(K(N+1,2))
 282         MSTJ(93)=1
 283         PSMC=PSMC+ULMASS_HIJING(K(N+2,2))
 284         IF(MAX(PS,PSMC)+PARJ(32).GT.PV(1,5)) GOTO 130
 285         HR1=(P(N+1,5)/PV(1,5))**2
 286         HR2=(P(N+2,5)/PV(1,5))**2
 287         IF((1.-HR1-HR2)*(2.+HR1+HR2)*SQRT((1.-HR1-HR2)**2-4.*HR1*HR2).
 288      &  LT.2.*RLU_HIJING(0)) GOTO 130
 289         ND=NP
 290
 291 C...Fully specified final state: check mass broadening effects.
 292       ELSE
 293         IF(NP.GE.2.AND.PS+PARJ(64).GT.PV(1,5)) GOTO 150
 294         ND=NP
 295       ENDIF
 296
 297 C...Select W mass in decay Q -> W + q, without W propagator.
 298       IF(MMAT.EQ.45.AND.MSTJ(25).LE.0) THEN
 299         HLQ=(PARJ(32)/PV(1,5))**2
 300         HUQ=(1.-(P(N+2,5)+PARJ(64))/PV(1,5))**2
 301         HRQ=(P(N+2,5)/PV(1,5))**2
 302   250   HW=HLQ+RLU_HIJING(0)*(HUQ-HLQ)
 303         IF(HMEPS(HW).LT.RLU_HIJING(0)) GOTO 250
 304         P(N+1,5)=PV(1,5)*SQRT(HW)
 305
 306 C...Ditto, including W propagator. Divide mass range into three regions.
 307       ELSEIF(MMAT.EQ.45) THEN
 308         HQW=(PV(1,5)/PMAS(24,1))**2
 309         HLW=(PARJ(32)/PMAS(24,1))**2
 310         HUW=((PV(1,5)-P(N+2,5)-PARJ(64))/PMAS(24,1))**2
 311         HRQ=(P(N+2,5)/PV(1,5))**2
 312         HG=PMAS(24,2)/PMAS(24,1)
 313         HATL=ATAN((HLW-1.)/HG)
 314         HM=MIN(1.,HUW-0.001)
 315         HMV1=HMEPS(HM/HQW)/((HM-1.)**2+HG**2)
 316   260   HM=HM-HG
 317         HMV2=HMEPS(HM/HQW)/((HM-1.)**2+HG**2)
 318         HSAV1=HMEPS(HM/HQW)
 319         HSAV2=1./((HM-1.)**2+HG**2)
 320         IF(HMV2.GT.HMV1.AND.HM-HG.GT.HLW) THEN
 321           HMV1=HMV2
 322           GOTO 260
 323         ENDIF
 324         HMV=MIN(2.*HMV1,HMEPS(HM/HQW)/HG**2)
 325         HM1=1.-SQRT(1./HMV-HG**2)
 326         IF(HM1.GT.HLW.AND.HM1.LT.HM) THEN
 327           HM=HM1
 328         ELSEIF(HMV2.LE.HMV1) THEN
 329           HM=MAX(HLW,HM-MIN(0.1,1.-HM))
 330         ENDIF
 331         HATM=ATAN((HM-1.)/HG)
 332         HWT1=(HATM-HATL)/HG
 333         HWT2=HMV*(MIN(1.,HUW)-HM)
 334         HWT3=0.
 335         IF(HUW.GT.1.) THEN
 336           HATU=ATAN((HUW-1.)/HG)
 337           HMP1=HMEPS(1./HQW)
 338           HWT3=HMP1*HATU/HG
 339         ENDIF
 340
 341 C...Select mass region and W mass there. Accept according to weight.
 342   270   HREG=RLU_HIJING(0)*(HWT1+HWT2+HWT3)
 343         IF(HREG.LE.HWT1) THEN
 344           HW=1.+HG*TAN(HATL+RLU_HIJING(0)*(HATM-HATL))
 345           HACC=HMEPS(HW/HQW)
 346         ELSEIF(HREG.LE.HWT1+HWT2) THEN
 347           HW=HM+RLU_HIJING(0)*(MIN(1.,HUW)-HM)
 348           HACC=HMEPS(HW/HQW)/((HW-1.)**2+HG**2)/HMV
 349         ELSE
 350           HW=1.+HG*TAN(RLU_HIJING(0)*HATU)
 351           HACC=HMEPS(HW/HQW)/HMP1
 352         ENDIF
 353         IF(HACC.LT.RLU_HIJING(0)) GOTO 270
 354         P(N+1,5)=PMAS(24,1)*SQRT(HW)
 355       ENDIF
 356
 357 C...Determine position of grandmother, number of sisters, Q -> W sign.
 358       NM=0
 359       MSGN=0
 360       IF(MMAT.EQ.3.OR.MMAT.EQ.46) THEN
 361         IM=K(IP,3)
 362         IF(IM.LT.0.OR.IM.GE.IP) IM=0
 363         IF(IM.NE.0) KFAM=IABS(K(IM,2))
 364         IF(IM.NE.0.AND.MMAT.EQ.3) THEN
 365           DO 280 IL=MAX(IP-2,IM+1),MIN(IP+2,N)
 366   280     IF(K(IL,3).EQ.IM) NM=NM+1
 367           IF(NM.NE.2.OR.KFAM.LE.100.OR.MOD(KFAM,10).NE.1.OR.
 368      &    MOD(KFAM/1000,10).NE.0) NM=0
 369         ELSEIF(IM.NE.0.AND.MMAT.EQ.46) THEN
 370           MSGN=ISIGN(1,K(IM,2)*K(IP,2))
 371           IF(KFAM.GT.100.AND.MOD(KFAM/1000,10).EQ.0) MSGN=
 372      &    MSGN*(-1)**MOD(KFAM/100,10)
 373         ENDIF
 374       ENDIF
 375
 376 C...Kinematics of one-particle decays.
 377       IF(ND.EQ.1) THEN
 378         DO 290 J=1,4
 379   290   P(N+1,J)=P(IP,J)
 380         GOTO 510
 381       ENDIF
 382
 383 C...Calculate maximum weight ND-particle decay.
 384       PV(ND,5)=P(N+ND,5)
 385       IF(ND.GE.3) THEN
 386         WTMAX=1./WTCOR(ND-2)
 387         PMAX=PV(1,5)-PS+P(N+ND,5)
 388         PMIN=0.
 389         DO 300 IL=ND-1,1,-1
 390         PMAX=PMAX+P(N+IL,5)
 391         PMIN=PMIN+P(N+IL+1,5)
 392   300   WTMAX=WTMAX*PAWT(PMAX,PMIN,P(N+IL,5))
 393       ENDIF
 394
 395 C...Find virtual gamma mass in Dalitz decay.
 396   310 IF(ND.EQ.2) THEN
 397       ELSEIF(MMAT.EQ.2) THEN
 398         PMES=4.*PMAS(11,1)**2
 399         PMRHO2=PMAS(131,1)**2
 400         PGRHO2=PMAS(131,2)**2
 401   320   PMST=PMES*(P(IP,5)**2/PMES)**RLU_HIJING(0)
 402         WT=(1+0.5*PMES/PMST)*SQRT(MAX(0.,1.-PMES/PMST))*
 403      &  (1.-PMST/P(IP,5)**2)**3*(1.+PGRHO2/PMRHO2)/
 404      &  ((1.-PMST/PMRHO2)**2+PGRHO2/PMRHO2)
 405         IF(WT.LT.RLU_HIJING(0)) GOTO 320
 406         PV(2,5)=MAX(2.00001*PMAS(11,1),SQRT(PMST))
 407
 408 C...M-generator gives weight. If rejected, try again.
 409       ELSE
 410   330   RORD(1)=1.
 411         DO 350 IL1=2,ND-1
 412         RSAV=RLU_HIJING(0)
 413         DO 340 IL2=IL1-1,1,-1
 414         IF(RSAV.LE.RORD(IL2)) GOTO 350
 415   340   RORD(IL2+1)=RORD(IL2)
 416   350   RORD(IL2+1)=RSAV
 417         RORD(ND)=0.
 418         WT=1.
 419         DO 360 IL=ND-1,1,-1
 420         PV(IL,5)=PV(IL+1,5)+P(N+IL,5)+(RORD(IL)-RORD(IL+1))*(PV(1,5)-PS)
 421   360   WT=WT*PAWT(PV(IL,5),PV(IL+1,5),P(N+IL,5))
 422         IF(WT.LT.RLU_HIJING(0)*WTMAX) GOTO 330
 423       ENDIF
 424
 425 C...Perform two-particle decays in respective CM frame.
 426   370 DO 390 IL=1,ND-1
 427       PA=PAWT(PV(IL,5),PV(IL+1,5),P(N+IL,5))
 428       UE(3)=2.*RLU_HIJING(0)-1.
 429       PHI=PARU(2)*RLU_HIJING(0)
 430       UE(1)=SQRT(1.-UE(3)**2)*COS(PHI)
 431       UE(2)=SQRT(1.-UE(3)**2)*SIN(PHI)
 432       DO 380 J=1,3
 433       P(N+IL,J)=PA*UE(J)
 434   380 PV(IL+1,J)=-PA*UE(J)
 435       P(N+IL,4)=SQRT(PA**2+P(N+IL,5)**2)
 436   390 PV(IL+1,4)=SQRT(PA**2+PV(IL+1,5)**2)
 437
 438 C...Lorentz transform decay products to lab frame.
 439       DO 400 J=1,4
 440   400 P(N+ND,J)=PV(ND,J)
 441       DO 430 IL=ND-1,1,-1
 442       DO 410 J=1,3
 443   410 BE(J)=PV(IL,J)/PV(IL,4)
 444       GA=PV(IL,4)/PV(IL,5)
 445       DO 430 I=N+IL,N+ND
 446       BEP=BE(1)*P(I,1)+BE(2)*P(I,2)+BE(3)*P(I,3)
 447       DO 420 J=1,3
 448   420 P(I,J)=P(I,J)+GA*(GA*BEP/(1.+GA)+P(I,4))*BE(J)
 449   430 P(I,4)=GA*(P(I,4)+BEP)
 450
 451 C...Matrix elements for omega and phi decays.
 452       IF(MMAT.EQ.1) THEN
 453         WT=(P(N+1,5)*P(N+2,5)*P(N+3,5))**2-(P(N+1,5)*FOUR(N+2,N+3))**2
 454      &  -(P(N+2,5)*FOUR(N+1,N+3))**2-(P(N+3,5)*FOUR(N+1,N+2))**2
 455      &  +2.*FOUR(N+1,N+2)*FOUR(N+1,N+3)*FOUR(N+2,N+3)
 456         IF(MAX(WT*WTCOR(9)/P(IP,5)**6,0.001).LT.RLU_HIJING(0)) GOTO 310
 457
 458 C...Matrix elements for pi0 or eta Dalitz decay to gamma e+ e-.
 459       ELSEIF(MMAT.EQ.2) THEN
 460         FOUR12=FOUR(N+1,N+2)
 461         FOUR13=FOUR(N+1,N+3)
 462         FOUR23=0.5*PMST-0.25*PMES
 463         WT=(PMST-0.5*PMES)*(FOUR12**2+FOUR13**2)+
 464      &  PMES*(FOUR12*FOUR13+FOUR12**2+FOUR13**2)
 465         IF(WT.LT.RLU_HIJING(0)*0.25*PMST*(P(IP,5)**2-PMST)**2) GOTO 370
 466
 467 C...Matrix element for S0 -> S1 + V1 -> S1 + S2 + S3 (S scalar,
 468 C...V vector), of form cos**2(theta02) in V1 rest frame.
 469       ELSEIF(MMAT.EQ.3.AND.NM.EQ.2) THEN
 470         IF((P(IP,5)**2*FOUR(IM,N+1)-FOUR(IP,IM)*FOUR(IP,N+1))**2.LE.
 471      &        RLU_HIJING(0)*(FOUR(IP,IM)**2-(P(IP,5)*P(IM,5))**2)
 472      $        *(FOUR(IP,N+1)**2-(P(IP,5)*P(N+1,5))**2)) GOTO 370
 473
 474 C...Matrix element for "onium" -> g + g + g or gamma + g + g.
 475       ELSEIF(MMAT.EQ.4) THEN
 476         HX1=2.*FOUR(IP,N+1)/P(IP,5)**2
 477         HX2=2.*FOUR(IP,N+2)/P(IP,5)**2
 478         HX3=2.*FOUR(IP,N+3)/P(IP,5)**2
 479         WT=((1.-HX1)/(HX2*HX3))**2+((1.-HX2)/(HX1*HX3))**2+
 480      &  ((1.-HX3)/(HX1*HX2))**2
 481         IF(WT.LT.2.*RLU_HIJING(0)) GOTO 310
 482         IF(K(IP+1,2).EQ.22.AND.(1.-HX1)*P(IP,5)**2.LT.4.*PARJ(32)**2)
 483      &  GOTO 310
 484
 485 C...Effective matrix element for nu spectrum in tau -> nu + hadrons.
 486       ELSEIF(MMAT.EQ.41) THEN
 487         HX1=2.*FOUR(IP,N+1)/P(IP,5)**2
 488         IF(8.*HX1*(3.-2.*HX1)/9..LT.RLU_HIJING(0)) GOTO 310
 489
 490 C...Matrix elements for weak decays (only semileptonic for c and b)
 491       ELSEIF(MMAT.GE.42.AND.MMAT.LE.44.AND.ND.EQ.3) THEN
 492         IF(MBST.EQ.0) WT=FOUR(IP,N+1)*FOUR(N+2,N+3)
 493         IF(MBST.EQ.1) WT=P(IP,5)*P(N+1,4)*FOUR(N+2,N+3)
 494         IF(WT.LT.RLU_HIJING(0)*P(IP,5)*PV(1,5)**3/WTCOR(10)) GOTO 310
 495       ELSEIF(MMAT.GE.42.AND.MMAT.LE.44) THEN
 496         DO 440 J=1,4
 497         P(N+NP+1,J)=0.
 498         DO 440 IS=N+3,N+NP
 499   440   P(N+NP+1,J)=P(N+NP+1,J)+P(IS,J)
 500         IF(MBST.EQ.0) WT=FOUR(IP,N+1)*FOUR(N+2,N+NP+1)
 501         IF(MBST.EQ.1) WT=P(IP,5)*P(N+1,4)*FOUR(N+2,N+NP+1)
 502         IF(WT.LT.RLU_HIJING(0)*P(IP,5)*PV(1,5)**3/WTCOR(10)) GOTO 310
 503
 504 C...Angular distribution in W decay.
 505       ELSEIF(MMAT.EQ.46.AND.MSGN.NE.0) THEN
 506         IF(MSGN.GT.0) WT=FOUR(IM,N+1)*FOUR(N+2,IP+1)
 507         IF(MSGN.LT.0) WT=FOUR(IM,N+2)*FOUR(N+1,IP+1)
 508         IF(WT.LT.RLU_HIJING(0)*P(IM,5)**4/WTCOR(10)) GOTO 370
 509       ENDIF
 510
 511 C...Scale back energy and reattach spectator.
 512       IF(MREM.EQ.1) THEN
 513         DO 450 J=1,5
 514   450   PV(1,J)=PV(1,J)/(1.-PQT)
 515         ND=ND+1
 516         MREM=0
 517       ENDIF
 518
 519 C...Low invariant mass for system with spectator quark gives particle,
 520 C...not two jets. Readjust momenta accordingly.
 521       IF((MMAT.EQ.31.OR.MMAT.EQ.45).AND.ND.EQ.3) THEN
 522         MSTJ(93)=1
 523         PM2=ULMASS_HIJING(K(N+2,2))
 524         MSTJ(93)=1
 525         PM3=ULMASS_HIJING(K(N+3,2))
 526         IF(P(N+2,5)**2+P(N+3,5)**2+2.*FOUR(N+2,N+3).GE.
 527      &  (PARJ(32)+PM2+PM3)**2) GOTO 510
 528         K(N+2,1)=1
 529         KFTEMP=K(N+2,2)
 530         CALL LUKFDI_HIJING(KFTEMP,K(N+3,2),KFLDMP,K(N+2,2))
 531         IF(K(N+2,2).EQ.0) GOTO 150
 532         P(N+2,5)=ULMASS_HIJING(K(N+2,2))
 533         PS=P(N+1,5)+P(N+2,5)
 534         PV(2,5)=P(N+2,5)
 535         MMAT=0
 536         ND=2
 537         GOTO 370
 538       ELSEIF(MMAT.EQ.44) THEN
 539         MSTJ(93)=1
 540         PM3=ULMASS_HIJING(K(N+3,2))
 541         MSTJ(93)=1
 542         PM4=ULMASS_HIJING(K(N+4,2))
 543         IF(P(N+3,5)**2+P(N+4,5)**2+2.*FOUR(N+3,N+4).GE.
 544      &  (PARJ(32)+PM3+PM4)**2) GOTO 480
 545         K(N+3,1)=1
 546         KFTEMP=K(N+3,2)
 547         CALL LUKFDI_HIJING(KFTEMP,K(N+4,2),KFLDMP,K(N+3,2))
 548         IF(K(N+3,2).EQ.0) GOTO 150
 549         P(N+3,5)=ULMASS_HIJING(K(N+3,2))
 550         DO 460 J=1,3
 551   460   P(N+3,J)=P(N+3,J)+P(N+4,J)
 552         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)
 553         HA=P(N+1,4)**2-P(N+2,4)**2
 554         HB=HA-(P(N+1,5)**2-P(N+2,5)**2)
 555         HC=(P(N+1,1)-P(N+2,1))**2+(P(N+1,2)-P(N+2,2))**2+
 556      &  (P(N+1,3)-P(N+2,3))**2
 557         HD=(PV(1,4)-P(N+3,4))**2
 558         HE=HA**2-2.*HD*(P(N+1,4)**2+P(N+2,4)**2)+HD**2
 559         HF=HD*HC-HB**2
 560         HG=HD*HC-HA*HB
 561         HH=(SQRT(HG**2+HE*HF)-HG)/(2.*HF)
 562         DO 470 J=1,3
 563         PCOR=HH*(P(N+1,J)-P(N+2,J))
 564         P(N+1,J)=P(N+1,J)+PCOR
 565   470   P(N+2,J)=P(N+2,J)-PCOR
 566         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)
 567         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)
 568         ND=ND-1
 569       ENDIF
 570
 571 C...Check invariant mass of W jets. May give one particle or start over.
 572   480 IF(MMAT.GE.42.AND.MMAT.LE.44.AND.IABS(K(N+1,2)).LT.10) THEN
 573         PMR=SQRT(MAX(0.,P(N+1,5)**2+P(N+2,5)**2+2.*FOUR(N+1,N+2)))
 574         MSTJ(93)=1
 575         PM1=ULMASS_HIJING(K(N+1,2))
 576         MSTJ(93)=1
 577         PM2=ULMASS_HIJING(K(N+2,2))
 578         IF(PMR.GT.PARJ(32)+PM1+PM2) GOTO 490
 579         KFLDUM=INT(1.5+RLU_HIJING(0))
 580         CALL LUKFDI_HIJING(K(N+1,2),-ISIGN(KFLDUM,K(N+1,2)),KFLDMP,KF1)
 581         CALL LUKFDI_HIJING(K(N+2,2),-ISIGN(KFLDUM,K(N+2,2)),KFLDMP,KF2)
 582         IF(KF1.EQ.0.OR.KF2.EQ.0) GOTO 150
 583         PSM=ULMASS_HIJING(KF1)+ULMASS_HIJING(KF2)
 584         IF(MMAT.EQ.42.AND.PMR.GT.PARJ(64)+PSM) GOTO 490
 585         IF(MMAT.GE.43.AND.PMR.GT.0.2*PARJ(32)+PSM) GOTO 490
 586         IF(ND.EQ.4.OR.KFA.EQ.15) GOTO 150
 587         K(N+1,1)=1
 588         KFTEMP=K(N+1,2)
 589         CALL LUKFDI_HIJING(KFTEMP,K(N+2,2),KFLDMP,K(N+1,2))
 590         IF(K(N+1,2).EQ.0) GOTO 150
 591         P(N+1,5)=ULMASS_HIJING(K(N+1,2))
 592         K(N+2,2)=K(N+3,2)
 593         P(N+2,5)=P(N+3,5)
 594         PS=P(N+1,5)+P(N+2,5)
 595         PV(2,5)=P(N+3,5)
 596         MMAT=0
 597         ND=2
 598         GOTO 370
 599       ENDIF
 600
 601 C...Phase space decay of partons from W decay.
 602   490 IF(MMAT.EQ.42.AND.IABS(K(N+1,2)).LT.10) THEN
 603         KFLO(1)=K(N+1,2)
 604         KFLO(2)=K(N+2,2)
 605         K(N+1,1)=K(N+3,1)
 606         K(N+1,2)=K(N+3,2)
 607         DO 500 J=1,5
 608         PV(1,J)=P(N+1,J)+P(N+2,J)
 609   500   P(N+1,J)=P(N+3,J)
 610         PV(1,5)=PMR
 611         N=N+1
 612         NP=0
 613         NQ=2
 614         PS=0.
 615         MSTJ(93)=2
 616         PSQ=ULMASS_HIJING(KFLO(1))
 617         MSTJ(93)=2
 618         PSQ=PSQ+ULMASS_HIJING(KFLO(2))
 619         MMAT=11
 620         GOTO 180
 621       ENDIF
 622
 623 C...Boost back for rapidly moving particle.
 624   510 N=N+ND
 625       IF(MBST.EQ.1) THEN
 626         DO 520 J=1,3
 627   520   BE(J)=P(IP,J)/P(IP,4)
 628         GA=P(IP,4)/P(IP,5)
 629         DO 540 I=NSAV+1,N
 630         BEP=BE(1)*P(I,1)+BE(2)*P(I,2)+BE(3)*P(I,3)
 631         DO 530 J=1,3
 632   530   P(I,J)=P(I,J)+GA*(GA*BEP/(1.+GA)+P(I,4))*BE(J)
 633   540   P(I,4)=GA*(P(I,4)+BEP)
 634       ENDIF
 635
 636 C...Fill in position of decay vertex.
 637       DO 560 I=NSAV+1,N
 638       DO 550 J=1,4
 639   550 V(I,J)=VDCY(J)
 640   560 V(I,5)=0.
 641
 642 C...Set up for parton shower evolution from jets.
 643       IF(MSTJ(23).GE.1.AND.MMAT.EQ.4.AND.K(NSAV+1,2).EQ.21) THEN
 644         K(NSAV+1,1)=3
 645         K(NSAV+2,1)=3
 646         K(NSAV+3,1)=3
 647         K(NSAV+1,4)=MSTU(5)*(NSAV+2)
 648         K(NSAV+1,5)=MSTU(5)*(NSAV+3)
 649         K(NSAV+2,4)=MSTU(5)*(NSAV+3)
 650         K(NSAV+2,5)=MSTU(5)*(NSAV+1)
 651         K(NSAV+3,4)=MSTU(5)*(NSAV+1)
 652         K(NSAV+3,5)=MSTU(5)*(NSAV+2)
 653         MSTJ(92)=-(NSAV+1)
 654       ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.4) THEN
 655         K(NSAV+2,1)=3
 656         K(NSAV+3,1)=3
 657         K(NSAV+2,4)=MSTU(5)*(NSAV+3)
 658         K(NSAV+2,5)=MSTU(5)*(NSAV+3)
 659         K(NSAV+3,4)=MSTU(5)*(NSAV+2)
 660         K(NSAV+3,5)=MSTU(5)*(NSAV+2)
 661         MSTJ(92)=NSAV+2
 662       ELSEIF(MSTJ(23).GE.1.AND.(MMAT.EQ.32.OR.MMAT.EQ.44.OR.MMAT.EQ.46).
 663      &AND.IABS(K(NSAV+1,2)).LE.10.AND.IABS(K(NSAV+2,2)).LE.10) THEN
 664         K(NSAV+1,1)=3
 665         K(NSAV+2,1)=3
 666         K(NSAV+1,4)=MSTU(5)*(NSAV+2)
 667         K(NSAV+1,5)=MSTU(5)*(NSAV+2)
 668         K(NSAV+2,4)=MSTU(5)*(NSAV+1)
 669         K(NSAV+2,5)=MSTU(5)*(NSAV+1)
 670         MSTJ(92)=NSAV+1
 671       ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.33.AND.IABS(K(NSAV+2,2)).EQ.21)
 672      &THEN
 673         K(NSAV+1,1)=3
 674         K(NSAV+2,1)=3
 675         K(NSAV+3,1)=3
 676         KCP=LUCOMP_HIJING(K(NSAV+1,2))
 677         KQP=KCHG(KCP,2)*ISIGN(1,K(NSAV+1,2))
 678         JCON=4
 679         IF(KQP.LT.0) JCON=5
 680         K(NSAV+1,JCON)=MSTU(5)*(NSAV+2)
 681         K(NSAV+2,9-JCON)=MSTU(5)*(NSAV+1)
 682         K(NSAV+2,JCON)=MSTU(5)*(NSAV+3)
 683         K(NSAV+3,9-JCON)=MSTU(5)*(NSAV+2)
 684         MSTJ(92)=NSAV+1
 685       ELSEIF(MSTJ(23).GE.1.AND.MMAT.EQ.33) THEN
 686         K(NSAV+1,1)=3
 687         K(NSAV+3,1)=3
 688         K(NSAV+1,4)=MSTU(5)*(NSAV+3)
 689         K(NSAV+1,5)=MSTU(5)*(NSAV+3)
 690         K(NSAV+3,4)=MSTU(5)*(NSAV+1)
 691         K(NSAV+3,5)=MSTU(5)*(NSAV+1)
 692         MSTJ(92)=NSAV+1
 693       ENDIF
 694
 695 C...Mark decayed particle.
 696       IF(K(IP,1).EQ.5) K(IP,1)=15
 697       IF(K(IP,1).LE.10) K(IP,1)=11
 698       K(IP,4)=NSAV+1
 699       K(IP,5)=N
 700
 701       RETURN
 702       END