2 C*********************************************************************
6 C...Purpose: to rearrange partons along strings, to allow small systems
7 C...to collapse into one or two particles and to check flavours.
8 IMPLICIT DOUBLE PRECISION(D)
9 COMMON/LUJETS/N,K(4000,5),P(4000,5),V(4000,5)
10 COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
11 COMMON/LUDAT2/KCHG(500,3),PMAS(500,4),PARF(2000),VCKM(4,4)
12 COMMON/LUDAT3/MDCY(500,3),MDME(2000,2),BRAT(2000),KFDP(2000,5)
13 SAVE /LUJETS/,/LUDAT1/,/LUDAT2/,/LUDAT3/
14 DIMENSION DPS(5),DPC(5),UE(3)
16 C...Rearrange parton shower product listing along strings: begin loop.
20 IF(K(I,1).NE.3) GOTO 120
24 IF(KQ.EQ.0.OR.(MQGST.EQ.1.AND.KQ.EQ.2)) GOTO 120
26 C...Pick up loose string end.
28 IF(KQ*ISIGN(1,K(I,2)).LT.0) KCS=5
33 CALL LUERRM(14,'(LUPREP:) caught in infinite loop')
37 C...Copy undecayed parton.
39 IF(I1.GE.MSTU(4)-MSTU(32)-5) THEN
40 CALL LUERRM(11,'(LUPREP:) no more memory left in LUJETS')
45 IF(NSTP.GE.2.AND.IABS(K(IA,2)).NE.21) K(I1,1)=1
55 IF(K(I1,1).EQ.1) GOTO 120
58 C...Go to next parton in colour space.
60 IF(MOD(K(IB,KCS)/MSTU(5)**2,2).EQ.0.AND.MOD(K(IB,KCS),MSTU(5))
62 IA=MOD(K(IB,KCS),MSTU(5))
63 K(IB,KCS)=K(IB,KCS)+MSTU(5)**2
66 IF(K(IB,KCS).GE.2*MSTU(5)**2.OR.MOD(K(IB,KCS)/MSTU(5),MSTU(5))
68 IA=MOD(K(IB,KCS)/MSTU(5),MSTU(5))
69 K(IB,KCS)=K(IB,KCS)+2*MSTU(5)**2
72 IF(IA.LE.0.OR.IA.GT.N) THEN
73 CALL LUERRM(12,'(LUPREP:) colour rearrangement failed')
76 IF(MOD(K(IA,4)/MSTU(5),MSTU(5)).EQ.IB.OR.MOD(K(IA,5)/MSTU(5),
78 IF(MREV.EQ.1) KCS=9-KCS
79 IF(MOD(K(IA,KCS)/MSTU(5),MSTU(5)).NE.IB) KCS=9-KCS
80 K(IA,KCS)=K(IA,KCS)+2*MSTU(5)**2
82 IF(MREV.EQ.0) KCS=9-KCS
83 IF(MOD(K(IA,KCS),MSTU(5)).NE.IB) KCS=9-KCS
84 K(IA,KCS)=K(IA,KCS)+MSTU(5)**2
91 IF(MSTJ(14).LT.0) RETURN
93 C...Find lowest-mass colour singlet jet system, OK if above threshold.
94 IF(MSTJ(14).EQ.0) GOTO 320
100 IF(K(I,1).NE.1.AND.K(I,1).NE.2) THEN
101 ELSEIF(K(I,1).EQ.2.AND.IC.EQ.0) THEN
108 DPS(5)=ULMASS(K(I,2))
109 ELSEIF(K(I,1).EQ.2) THEN
113 ELSEIF(IC.NE.0.AND.KCHG(LUCOMP(K(I,2)),2).NE.0) THEN
118 DPS(5)=DPS(5)+ULMASS(K(I,2))
119 PD=SQRT(MAX(0D0,DPS(4)**2-DPS(1)**2-DPS(2)**2-DPS(3)**2))-DPS(5)
133 IF(PDM.GE.PARJ(32)) GOTO 320
135 C...Fill small-mass system as cluster.
137 PECM=SQRT(MAX(0D0,DPC(4)**2-DPC(1)**2-DPC(2)**2-DPC(3)**2))
149 C...Form two particles from flavours of lowest-mass system, if feasible.
152 IF(MSTU(16).NE.2) THEN
163 IF(IABS(K(IC1,2)).NE.21) THEN
166 IF(KC1.EQ.0.OR.KC2.EQ.0) GOTO 320
167 KQ1=KCHG(KC1,2)*ISIGN(1,K(IC1,2))
168 KQ2=KCHG(KC2,2)*ISIGN(1,K(IC2,2))
169 IF(KQ1+KQ2.NE.0) GOTO 320
170 200 CALL LUKFDI(K(IC1,2),0,KFLN,K(N+2,2))
171 CALL LUKFDI(K(IC2,2),-KFLN,KFLDMP,K(N+3,2))
172 IF(K(N+2,2).EQ.0.OR.K(N+3,2).EQ.0) GOTO 200
174 IF(IABS(K(IC2,2)).NE.21) GOTO 320
175 210 CALL LUKFDI(1+INT((2.+PARJ(2))*RLU(0)),0,KFLN,KFDMP)
176 CALL LUKFDI(KFLN,0,KFLM,K(N+2,2))
177 CALL LUKFDI(-KFLN,-KFLM,KFLDMP,K(N+3,2))
178 IF(K(N+2,2).EQ.0.OR.K(N+3,2).EQ.0) GOTO 210
180 P(N+2,5)=ULMASS(K(N+2,2))
181 P(N+3,5)=ULMASS(K(N+3,2))
182 IF(P(N+2,5)+P(N+3,5)+PARJ(64).GE.PECM.AND.NSIN.EQ.1) GOTO 320
183 IF(P(N+2,5)+P(N+3,5)+PARJ(64).GE.PECM) GOTO 260
185 C...Perform two-particle decay of jet system, if possible.
186 IF(PECM.GE.0.02*DPC(4)) THEN
187 PA=SQRT((PECM**2-(P(N+2,5)+P(N+3,5))**2)*(PECM**2-
188 & (P(N+2,5)-P(N+3,5))**2))/(2.*PECM)
191 UE(1)=SQRT(1.-UE(3)**2)*COS(PHI)
192 UE(2)=SQRT(1.-UE(3)**2)*SIN(PHI)
197 P(N+2,4)=SQRT(PA**2+P(N+2,5)**2)
198 P(N+3,4)=SQRT(PA**2+P(N+3,5)**2)
200 CALL LUDBRB(N+2,N+3,0.,0.,DPC(1)/DPC(4),DPC(2)/DPC(4),
205 IF(K(I,1).EQ.1.OR.K(I,1).EQ.2) NP=NP+1
207 HA=P(IC1,4)*P(IC2,4)-P(IC1,1)*P(IC2,1)-P(IC1,2)*P(IC2,2)-
209 IF(NP.GE.3.OR.HA.LE.1.25*P(IC1,5)*P(IC2,5)) GOTO 260
210 HD1=0.5*(P(N+2,5)**2-P(IC1,5)**2)
211 HD2=0.5*(P(N+3,5)**2-P(IC2,5)**2)
212 HR=SQRT(MAX(0.,((HA-HD1-HD2)**2-(P(N+2,5)*P(N+3,5))**2)/
213 & (HA**2-(P(IC1,5)*P(IC2,5))**2)))-1.
214 HC=P(IC1,5)**2+2.*HA+P(IC2,5)**2
215 HK1=((P(IC2,5)**2+HA)*HR+HD1-HD2)/HC
216 HK2=((P(IC1,5)**2+HA)*HR+HD2-HD1)/HC
218 P(N+2,J)=(1.+HK1)*P(IC1,J)-HK2*P(IC2,J)
219 P(N+3,J)=(1.+HK2)*P(IC2,J)-HK1*P(IC1,J)
233 C...Else form one particle from the flavours available, if possible.
235 IF(IABS(K(IC1,2)).GT.100.AND.IABS(K(IC2,2)).GT.100) THEN
237 ELSEIF(IABS(K(IC1,2)).NE.21) THEN
238 CALL LUKFDI(K(IC1,2),K(IC2,2),KFLDMP,K(N+2,2))
240 KFLN=1+INT((2.+PARJ(2))*RLU(0))
241 CALL LUKFDI(KFLN,-KFLN,KFLDMP,K(N+2,2))
243 IF(K(N+2,2).EQ.0) GOTO 260
244 P(N+2,5)=ULMASS(K(N+2,2))
246 C...Find parton/particle which combines to largest extra mass.
253 IF(K(I,1).LE.0.OR.K(I,1).GT.10.OR.(I.GE.IC1.AND.I.LE.IC2
254 &.AND.K(I,1).GE.1.AND.K(I,1).LE.2)) GOTO 270
255 IF(MCOMB.EQ.1) KCI=LUCOMP(K(I,2))
256 IF(MCOMB.EQ.1.AND.KCI.EQ.0) GOTO 270
257 IF(MCOMB.EQ.1.AND.KCHG(KCI,2).EQ.0.AND.I.LE.NS) GOTO 270
258 IF(MCOMB.EQ.2.AND.IABS(K(I,2)).GT.10.AND.IABS(K(I,2)).LE.100)
260 HCR=DPC(4)*P(I,4)-DPC(1)*P(I,1)-DPC(2)*P(I,2)-DPC(3)*P(I,3)
261 HSR=2.*HCR+PECM**2-P(N+2,5)**2-2.*P(N+2,5)*P(I,5)
270 C...Shuffle energy and momentum to put new particle on mass shell.
275 HK2=0.5*(HB*SQRT(MAX(0.,((HB+HC)**2-4.*(HB+HD)*P(N+2,5)**2)/
276 & (HA**2-(PECM*P(IR,5))**2)))-(HB+HC))/(HB+HD)
277 HK1=(0.5*(P(N+2,5)**2-PECM**2)+HD*HK2)/HB
279 P(N+2,J)=(1.+HK1)*DPC(J)-HK2*P(IR,J)
280 P(IR,J)=(1.+HK2)*P(IR,J)-HK1*DPC(J)
288 CALL LUERRM(3,'(LUPREP:) no match for collapsing cluster')
292 C...Mark collapsed system and store daughter pointers. Iterate.
294 IF((K(I,1).EQ.1.OR.K(I,1).EQ.2).AND.KCHG(LUCOMP(K(I,2)),2).NE.0)
297 IF(MSTU(16).NE.2) THEN
306 IF(N.LT.MSTU(4)-MSTU(32)-5) GOTO 140
308 C...Check flavours and invariant masses in parton systems.
316 IF(K(I,1).LE.0.OR.K(I,1).GT.10) GOTO 360
319 KQ=KCHG(KC,2)*ISIGN(1,K(I,2))
326 DPS(5)=DPS(5)+ULMASS(K(I,2))
332 IF(NP.NE.1.AND.(KFN.EQ.1.OR.KFN.GE.3.OR.KQS.NE.0)) CALL
333 & LUERRM(2,'(LUPREP:) unphysical flavour combination')
334 IF(NP.NE.1.AND.DPS(4)**2-DPS(1)**2-DPS(2)**2-DPS(3)**2.LT.
335 & (0.9*PARJ(32)+DPS(5))**2) CALL LUERRM(3,
336 & '(LUPREP:) too small mass in jet system')