* $Id$ C********************************************************************* SUBROUTINE LUSTRF_HIJING(IP) C...Purpose: to handle the fragmentation of an arbitrary colour singlet C...jet system according to the Lund string fragmentation model. IMPLICIT DOUBLE PRECISION(D) #include "lujets_hijing.inc" #include "ludat1_hijing.inc" #include "ludat2_hijing.inc" DIMENSION DPS(5),KFL(3),PMQ(3),PX(3),PY(3),GAM(3),IE(2),PR(2), &IN(9),DHM(4),DHG(4),DP(5,5),IRANK(2),MJU(4),IJU(3),PJU(5,5), &TJU(5),KFJH(2),NJS(2),KFJS(2),PJS(4,5) C...Function: four-product of two vectors. 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) DFOUR(I,J)=DP(I,4)*DP(J,4)-DP(I,1)*DP(J,1)-DP(I,2)*DP(J,2)- &DP(I,3)*DP(J,3) C...Reset counters. Identify parton system. MSTJ(91)=0 NSAV=N NP=0 KQSUM=0 DO 100 J=1,5 100 DPS(J)=0. MJU(1)=0 MJU(2)=0 I=IP-1 110 I=I+1 IF(I.GT.MIN(N,MSTU(4)-MSTU(32))) THEN CALL LUERRM_HIJING(12 $ ,'(LUSTRF_HIJING:) failed to reconstruct jet system') IF(MSTU(21).GE.1) RETURN ENDIF IF(K(I,1).NE.1.AND.K(I,1).NE.2.AND.K(I,1).NE.41) GOTO 110 KC=LUCOMP_HIJING(K(I,2)) IF(KC.EQ.0) GOTO 110 KQ=KCHG(KC,2)*ISIGN(1,K(I,2)) IF(KQ.EQ.0) GOTO 110 IF(N+5*NP+11.GT.MSTU(4)-MSTU(32)-5) THEN CALL LUERRM_HIJING(11 $ ,'(LUSTRF_HIJING:) no more memory left in LUJETS_HIJING') IF(MSTU(21).GE.1) RETURN ENDIF C...Take copy of partons to be considered. Check flavour sum. NP=NP+1 DO 120 J=1,5 K(N+NP,J)=K(I,J) P(N+NP,J)=P(I,J) 120 DPS(J)=DPS(J)+P(I,J) K(N+NP,3)=I IF(P(N+NP,4)**2.LT.P(N+NP,1)**2+P(N+NP,2)**2+P(N+NP,3)**2) THEN P(N+NP,4)=SQRT(P(N+NP,1)**2+P(N+NP,2)**2+P(N+NP,3)**2+ & P(N+NP,5)**2) DPS(4)=DPS(4)+MAX(0.,P(N+NP,4)-P(I,4)) ENDIF IF(KQ.NE.2) KQSUM=KQSUM+KQ IF(K(I,1).EQ.41) THEN KQSUM=KQSUM+2*KQ IF(KQSUM.EQ.KQ) MJU(1)=N+NP IF(KQSUM.NE.KQ) MJU(2)=N+NP ENDIF IF(K(I,1).EQ.2.OR.K(I,1).EQ.41) GOTO 110 IF(KQSUM.NE.0) THEN CALL LUERRM_HIJING(12 $ ,'(LUSTRF_HIJING:) unphysical flavour combination') IF(MSTU(21).GE.1) RETURN ENDIF C...Boost copied system to CM frame (for better numerical precision). CALL LUDBRB_HIJING(N+1,N+NP,0.,0.,-DPS(1)/DPS(4),-DPS(2)/DPS(4), &-DPS(3)/DPS(4)) C...Search for very nearby partons that may be recombined. NTRYR=0 PARU12=PARU(12) PARU13=PARU(13) MJU(3)=MJU(1) MJU(4)=MJU(2) NR=NP 130 IF(NR.GE.3) THEN PDRMIN=2.*PARU12 DO 140 I=N+1,N+NR IF(I.EQ.N+NR.AND.IABS(K(N+1,2)).NE.21) GOTO 140 I1=I+1 IF(I.EQ.N+NR) I1=N+1 IF(K(I,1).EQ.41.OR.K(I1,1).EQ.41) GOTO 140 IF(MJU(1).NE.0.AND.I1.LT.MJU(1).AND.IABS(K(I1,2)).NE.21) & GOTO 140 IF(MJU(2).NE.0.AND.I.GT.MJU(2).AND.IABS(K(I,2)).NE.21) GOTO 140 PAP=SQRT((P(I,1)**2+P(I,2)**2+P(I,3)**2)*(P(I1,1)**2+ & P(I1,2)**2+P(I1,3)**2)) PVP=P(I,1)*P(I1,1)+P(I,2)*P(I1,2)+P(I,3)*P(I1,3) PDR=4.*(PAP-PVP)**2/(PARU13**2*PAP+2.*(PAP-PVP)) IF(PDR.LT.PDRMIN) THEN IR=I PDRMIN=PDR ENDIF 140 CONTINUE C...Recombine very nearby partons to avoid machine precision problems. IF(PDRMIN.LT.PARU12.AND.IR.EQ.N+NR) THEN DO 150 J=1,4 150 P(N+1,J)=P(N+1,J)+P(N+NR,J) P(N+1,5)=SQRT(MAX(0.,P(N+1,4)**2-P(N+1,1)**2-P(N+1,2)**2- & P(N+1,3)**2)) NR=NR-1 GOTO 130 ELSEIF(PDRMIN.LT.PARU12) THEN DO 160 J=1,4 160 P(IR,J)=P(IR,J)+P(IR+1,J) P(IR,5)=SQRT(MAX(0.,P(IR,4)**2-P(IR,1)**2-P(IR,2)**2- & P(IR,3)**2)) DO 170 I=IR+1,N+NR-1 K(I,2)=K(I+1,2) DO 170 J=1,5 170 P(I,J)=P(I+1,J) IF(IR.EQ.N+NR-1) K(IR,2)=K(N+NR,2) NR=NR-1 IF(MJU(1).GT.IR) MJU(1)=MJU(1)-1 IF(MJU(2).GT.IR) MJU(2)=MJU(2)-1 GOTO 130 ENDIF ENDIF NTRYR=NTRYR+1 C...Reset particle counter. Skip ahead if no junctions are present; C...this is usually the case! NRS=MAX(5*NR+11,NP) NTRY=0 180 NTRY=NTRY+1 IF(NTRY.GT.100.AND.NTRYR.LE.4) THEN PARU12=4.*PARU12 PARU13=2.*PARU13 GOTO 130 ELSEIF(NTRY.GT.100) THEN CALL LUERRM_HIJING(14 $ ,'(LUSTRF_HIJING:) caught in infinite loop') IF(MSTU(21).GE.1) RETURN ENDIF I=N+NRS IF(MJU(1).EQ.0.AND.MJU(2).EQ.0) GOTO 500 DO 490 JT=1,2 NJS(JT)=0 IF(MJU(JT).EQ.0) GOTO 490 JS=3-2*JT C...Find and sum up momentum on three sides of junction. Check flavours. DO 190 IU=1,3 IJU(IU)=0 DO 190 J=1,5 190 PJU(IU,J)=0. IU=0 DO 200 I1=N+1+(JT-1)*(NR-1),N+NR+(JT-1)*(1-NR),JS IF(K(I1,2).NE.21.AND.IU.LE.2) THEN IU=IU+1 IJU(IU)=I1 ENDIF DO 200 J=1,4 200 PJU(IU,J)=PJU(IU,J)+P(I1,J) DO 210 IU=1,3 210 PJU(IU,5)=SQRT(PJU(IU,1)**2+PJU(IU,2)**2+PJU(IU,3)**2) IF(K(IJU(3),2)/100.NE.10*K(IJU(1),2)+K(IJU(2),2).AND. &K(IJU(3),2)/100.NE.10*K(IJU(2),2)+K(IJU(1),2)) THEN CALL LUERRM_HIJING(12 $ ,'(LUSTRF_HIJING:) unphysical flavour combination') IF(MSTU(21).GE.1) RETURN ENDIF C...Calculate (approximate) boost to rest frame of junction. T12=(PJU(1,1)*PJU(2,1)+PJU(1,2)*PJU(2,2)+PJU(1,3)*PJU(2,3))/ &(PJU(1,5)*PJU(2,5)) T13=(PJU(1,1)*PJU(3,1)+PJU(1,2)*PJU(3,2)+PJU(1,3)*PJU(3,3))/ &(PJU(1,5)*PJU(3,5)) T23=(PJU(2,1)*PJU(3,1)+PJU(2,2)*PJU(3,2)+PJU(2,3)*PJU(3,3))/ &(PJU(2,5)*PJU(3,5)) T11=SQRT((2./3.)*(1.-T12)*(1.-T13)/(1.-T23)) T22=SQRT((2./3.)*(1.-T12)*(1.-T23)/(1.-T13)) TSQ=SQRT((2.*T11*T22+T12-1.)*(1.+T12)) T1F=(TSQ-T22*(1.+T12))/(1.-T12**2) T2F=(TSQ-T11*(1.+T12))/(1.-T12**2) DO 220 J=1,3 220 TJU(J)=-(T1F*PJU(1,J)/PJU(1,5)+T2F*PJU(2,J)/PJU(2,5)) TJU(4)=SQRT(1.+TJU(1)**2+TJU(2)**2+TJU(3)**2) DO 230 IU=1,3 230 PJU(IU,5)=TJU(4)*PJU(IU,4)-TJU(1)*PJU(IU,1)-TJU(2)*PJU(IU,2)- &TJU(3)*PJU(IU,3) C...Put junction at rest if motion could give inconsistencies. IF(PJU(1,5)+PJU(2,5).GT.PJU(1,4)+PJU(2,4)) THEN DO 240 J=1,3 240 TJU(J)=0. TJU(4)=1. PJU(1,5)=PJU(1,4) PJU(2,5)=PJU(2,4) PJU(3,5)=PJU(3,4) ENDIF C...Start preparing for fragmentation of two strings from junction. ISTA=I DO 470 IU=1,2 NS=IJU(IU+1)-IJU(IU) C...Junction strings: find longitudinal string directions. DO 260 IS=1,NS IS1=IJU(IU)+IS-1 IS2=IJU(IU)+IS DO 250 J=1,5 DP(1,J)=0.5*P(IS1,J) IF(IS.EQ.1) DP(1,J)=P(IS1,J) DP(2,J)=0.5*P(IS2,J) 250 IF(IS.EQ.NS) DP(2,J)=-PJU(IU,J) IF(IS.EQ.NS) DP(2,4)=SQRT(PJU(IU,1)**2+PJU(IU,2)**2+PJU(IU,3)**2) IF(IS.EQ.NS) DP(2,5)=0. DP(3,5)=DFOUR(1,1) DP(4,5)=DFOUR(2,2) DHKC=DFOUR(1,2) IF(DP(3,5)+2.*DHKC+DP(4,5).LE.0.) THEN DP(1,4)=SQRT(DP(1,1)**2+DP(1,2)**2+DP(1,3)**2) DP(2,4)=SQRT(DP(2,1)**2+DP(2,2)**2+DP(2,3)**2) DP(3,5)=0D0 DP(4,5)=0D0 DHKC=DFOUR(1,2) ENDIF DHKS=SQRT(DHKC**2-DP(3,5)*DP(4,5)) DHK1=0.5*((DP(4,5)+DHKC)/DHKS-1.) DHK2=0.5*((DP(3,5)+DHKC)/DHKS-1.) IN1=N+NR+4*IS-3 P(IN1,5)=SQRT(DP(3,5)+2.*DHKC+DP(4,5)) DO 260 J=1,4 P(IN1,J)=(1.+DHK1)*DP(1,J)-DHK2*DP(2,J) 260 P(IN1+1,J)=(1.+DHK2)*DP(2,J)-DHK1*DP(1,J) C...Junction strings: initialize flavour, momentum and starting pos. ISAV=I 270 NTRY=NTRY+1 IF(NTRY.GT.100.AND.NTRYR.LE.4) THEN PARU12=4.*PARU12 PARU13=2.*PARU13 GOTO 130 ELSEIF(NTRY.GT.100) THEN CALL LUERRM_HIJING(14 $ ,'(LUSTRF_HIJING:) caught in infinite loop') IF(MSTU(21).GE.1) RETURN ENDIF I=ISAV IRANKJ=0 IE(1)=K(N+1+(JT/2)*(NP-1),3) IN(4)=N+NR+1 IN(5)=IN(4)+1 IN(6)=N+NR+4*NS+1 DO 280 JQ=1,2 DO 280 IN1=N+NR+2+JQ,N+NR+4*NS-2+JQ,4 P(IN1,1)=2-JQ P(IN1,2)=JQ-1 280 P(IN1,3)=1. KFL(1)=K(IJU(IU),2) PX(1)=0. PY(1)=0. GAM(1)=0. DO 290 J=1,5 290 PJU(IU+3,J)=0. C...Junction strings: find initial transverse directions. DO 300 J=1,4 DP(1,J)=P(IN(4),J) DP(2,J)=P(IN(4)+1,J) DP(3,J)=0. 300 DP(4,J)=0. DP(1,4)=SQRT(DP(1,1)**2+DP(1,2)**2+DP(1,3)**2) DP(2,4)=SQRT(DP(2,1)**2+DP(2,2)**2+DP(2,3)**2) DP(5,1)=DP(1,1)/DP(1,4)-DP(2,1)/DP(2,4) DP(5,2)=DP(1,2)/DP(1,4)-DP(2,2)/DP(2,4) DP(5,3)=DP(1,3)/DP(1,4)-DP(2,3)/DP(2,4) IF(DP(5,1)**2.LE.DP(5,2)**2+DP(5,3)**2) DP(3,1)=1. IF(DP(5,1)**2.GT.DP(5,2)**2+DP(5,3)**2) DP(3,3)=1. IF(DP(5,2)**2.LE.DP(5,1)**2+DP(5,3)**2) DP(4,2)=1. IF(DP(5,2)**2.GT.DP(5,1)**2+DP(5,3)**2) DP(4,3)=1. DHC12=DFOUR(1,2) DHCX1=DFOUR(3,1)/DHC12 DHCX2=DFOUR(3,2)/DHC12 DHCXX=1D0/SQRT(1D0+2D0*DHCX1*DHCX2*DHC12) DHCY1=DFOUR(4,1)/DHC12 DHCY2=DFOUR(4,2)/DHC12 DHCYX=DHCXX*(DHCX1*DHCY2+DHCX2*DHCY1)*DHC12 DHCYY=1D0/SQRT(1D0+2D0*DHCY1*DHCY2*DHC12-DHCYX**2) DO 310 J=1,4 DP(3,J)=DHCXX*(DP(3,J)-DHCX2*DP(1,J)-DHCX1*DP(2,J)) P(IN(6),J)=DP(3,J) 310 P(IN(6)+1,J)=DHCYY*(DP(4,J)-DHCY2*DP(1,J)-DHCY1*DP(2,J)- &DHCYX*DP(3,J)) C...Junction strings: produce new particle, origin. 320 I=I+1 IF(2*I-NSAV.GE.MSTU(4)-MSTU(32)-5) THEN CALL LUERRM_HIJING(11 $ ,'(LUSTRF_HIJING:) no more memory left in LUJETS_HIJING') IF(MSTU(21).GE.1) RETURN ENDIF IRANKJ=IRANKJ+1 K(I,1)=1 K(I,3)=IE(1) K(I,4)=0 K(I,5)=0 C...Junction strings: generate flavour, hadron, pT, z and Gamma. 330 CALL LUKFDI_HIJING(KFL(1),0,KFL(3),K(I,2)) IF(K(I,2).EQ.0) GOTO 270 IF(MSTJ(12).GE.3.AND.IRANKJ.EQ.1.AND.IABS(KFL(1)).LE.10.AND. &IABS(KFL(3)).GT.10) THEN IF(RLU_HIJING(0).GT.PARJ(19)) GOTO 330 ENDIF P(I,5)=ULMASS_HIJING(K(I,2)) CALL LUPTDI_HIJING(KFL(1),PX(3),PY(3)) PR(1)=P(I,5)**2+(PX(1)+PX(3))**2+(PY(1)+PY(3))**2 CALL LUZDIS_HIJING(KFL(1),KFL(3),PR(1),Z) GAM(3)=(1.-Z)*(GAM(1)+PR(1)/Z) DO 340 J=1,3 340 IN(J)=IN(3+J) C...Junction strings: stepping within or from 'low' string region easy. IF(IN(1)+1.EQ.IN(2).AND.Z*P(IN(1)+2,3)*P(IN(2)+2,3)* &P(IN(1),5)**2.GE.PR(1)) THEN P(IN(1)+2,4)=Z*P(IN(1)+2,3) P(IN(2)+2,4)=PR(1)/(P(IN(1)+2,4)*P(IN(1),5)**2) DO 350 J=1,4 350 P(I,J)=(PX(1)+PX(3))*P(IN(3),J)+(PY(1)+PY(3))*P(IN(3)+1,J) GOTO 420 ELSEIF(IN(1)+1.EQ.IN(2)) THEN P(IN(2)+2,4)=P(IN(2)+2,3) P(IN(2)+2,1)=1. IN(2)=IN(2)+4 IF(IN(2).GT.N+NR+4*NS) GOTO 270 IF(FOUR(IN(1),IN(2)).LE.1E-2) THEN P(IN(1)+2,4)=P(IN(1)+2,3) P(IN(1)+2,1)=0. IN(1)=IN(1)+4 ENDIF ENDIF C...Junction strings: find new transverse directions. 360 IF(IN(1).GT.N+NR+4*NS.OR.IN(2).GT.N+NR+4*NS.OR. &IN(1).GT.IN(2)) GOTO 270 IF(IN(1).NE.IN(4).OR.IN(2).NE.IN(5)) THEN DO 370 J=1,4 DP(1,J)=P(IN(1),J) DP(2,J)=P(IN(2),J) DP(3,J)=0. 370 DP(4,J)=0. DP(1,4)=SQRT(DP(1,1)**2+DP(1,2)**2+DP(1,3)**2) DP(2,4)=SQRT(DP(2,1)**2+DP(2,2)**2+DP(2,3)**2) DHC12=DFOUR(1,2) IF(DHC12.LE.1E-2) THEN P(IN(1)+2,4)=P(IN(1)+2,3) P(IN(1)+2,1)=0. IN(1)=IN(1)+4 GOTO 360 ENDIF IN(3)=N+NR+4*NS+5 DP(5,1)=DP(1,1)/DP(1,4)-DP(2,1)/DP(2,4) DP(5,2)=DP(1,2)/DP(1,4)-DP(2,2)/DP(2,4) DP(5,3)=DP(1,3)/DP(1,4)-DP(2,3)/DP(2,4) IF(DP(5,1)**2.LE.DP(5,2)**2+DP(5,3)**2) DP(3,1)=1. IF(DP(5,1)**2.GT.DP(5,2)**2+DP(5,3)**2) DP(3,3)=1. IF(DP(5,2)**2.LE.DP(5,1)**2+DP(5,3)**2) DP(4,2)=1. IF(DP(5,2)**2.GT.DP(5,1)**2+DP(5,3)**2) DP(4,3)=1. DHCX1=DFOUR(3,1)/DHC12 DHCX2=DFOUR(3,2)/DHC12 DHCXX=1D0/SQRT(1D0+2D0*DHCX1*DHCX2*DHC12) DHCY1=DFOUR(4,1)/DHC12 DHCY2=DFOUR(4,2)/DHC12 DHCYX=DHCXX*(DHCX1*DHCY2+DHCX2*DHCY1)*DHC12 DHCYY=1D0/SQRT(1D0+2D0*DHCY1*DHCY2*DHC12-DHCYX**2) DO 380 J=1,4 DP(3,J)=DHCXX*(DP(3,J)-DHCX2*DP(1,J)-DHCX1*DP(2,J)) P(IN(3),J)=DP(3,J) 380 P(IN(3)+1,J)=DHCYY*(DP(4,J)-DHCY2*DP(1,J)-DHCY1*DP(2,J)- & DHCYX*DP(3,J)) C...Express pT with respect to new axes, if sensible. PXP=-(PX(3)*FOUR(IN(6),IN(3))+PY(3)*FOUR(IN(6)+1,IN(3))) PYP=-(PX(3)*FOUR(IN(6),IN(3)+1)+PY(3)*FOUR(IN(6)+1,IN(3)+1)) IF(ABS(PXP**2+PYP**2-PX(3)**2-PY(3)**2).LT.0.01) THEN PX(3)=PXP PY(3)=PYP ENDIF ENDIF C...Junction strings: sum up known four-momentum, coefficients for m2. DO 400 J=1,4 DHG(J)=0. P(I,J)=PX(1)*P(IN(6),J)+PY(1)*P(IN(6)+1,J)+PX(3)*P(IN(3),J)+ &PY(3)*P(IN(3)+1,J) DO 390 IN1=IN(4),IN(1)-4,4 390 P(I,J)=P(I,J)+P(IN1+2,3)*P(IN1,J) DO 400 IN2=IN(5),IN(2)-4,4 400 P(I,J)=P(I,J)+P(IN2+2,3)*P(IN2,J) DHM(1)=FOUR(I,I) DHM(2)=2.*FOUR(I,IN(1)) DHM(3)=2.*FOUR(I,IN(2)) DHM(4)=2.*FOUR(IN(1),IN(2)) C...Junction strings: find coefficients for Gamma expression. DO 410 IN2=IN(1)+1,IN(2),4 DO 410 IN1=IN(1),IN2-1,4 DHC=2.*FOUR(IN1,IN2) DHG(1)=DHG(1)+P(IN1+2,1)*P(IN2+2,1)*DHC IF(IN1.EQ.IN(1)) DHG(2)=DHG(2)-P(IN2+2,1)*DHC IF(IN2.EQ.IN(2)) DHG(3)=DHG(3)+P(IN1+2,1)*DHC 410 IF(IN1.EQ.IN(1).AND.IN2.EQ.IN(2)) DHG(4)=DHG(4)-DHC C...Junction strings: solve (m2, Gamma) equation system for energies. DHS1=DHM(3)*DHG(4)-DHM(4)*DHG(3) IF(ABS(DHS1).LT.1E-4) GOTO 270 DHS2=DHM(4)*(GAM(3)-DHG(1))-DHM(2)*DHG(3)-DHG(4)* &(P(I,5)**2-DHM(1))+DHG(2)*DHM(3) DHS3=DHM(2)*(GAM(3)-DHG(1))-DHG(2)*(P(I,5)**2-DHM(1)) P(IN(2)+2,4)=0.5*(SQRT(MAX(0D0,DHS2**2-4.*DHS1*DHS3))/ABS(DHS1)- &DHS2/DHS1) IF(DHM(2)+DHM(4)*P(IN(2)+2,4).LE.0.) GOTO 270 P(IN(1)+2,4)=(P(I,5)**2-DHM(1)-DHM(3)*P(IN(2)+2,4))/ &(DHM(2)+DHM(4)*P(IN(2)+2,4)) C...Junction strings: step to new region if necessary. IF(P(IN(2)+2,4).GT.P(IN(2)+2,3)) THEN P(IN(2)+2,4)=P(IN(2)+2,3) P(IN(2)+2,1)=1. IN(2)=IN(2)+4 IF(IN(2).GT.N+NR+4*NS) GOTO 270 IF(FOUR(IN(1),IN(2)).LE.1E-2) THEN P(IN(1)+2,4)=P(IN(1)+2,3) P(IN(1)+2,1)=0. IN(1)=IN(1)+4 ENDIF GOTO 360 ELSEIF(P(IN(1)+2,4).GT.P(IN(1)+2,3)) THEN P(IN(1)+2,4)=P(IN(1)+2,3) P(IN(1)+2,1)=0. IN(1)=IN(1)+JS GOTO 710 ENDIF C...Junction strings: particle four-momentum, remainder, loop back. 420 DO 430 J=1,4 P(I,J)=P(I,J)+P(IN(1)+2,4)*P(IN(1),J)+P(IN(2)+2,4)*P(IN(2),J) 430 PJU(IU+3,J)=PJU(IU+3,J)+P(I,J) IF(P(I,4).LE.0.) GOTO 270 PJU(IU+3,5)=TJU(4)*PJU(IU+3,4)-TJU(1)*PJU(IU+3,1)- &TJU(2)*PJU(IU+3,2)-TJU(3)*PJU(IU+3,3) IF(PJU(IU+3,5).LT.PJU(IU,5)) THEN KFL(1)=-KFL(3) PX(1)=-PX(3) PY(1)=-PY(3) GAM(1)=GAM(3) IF(IN(3).NE.IN(6)) THEN DO 440 J=1,4 P(IN(6),J)=P(IN(3),J) 440 P(IN(6)+1,J)=P(IN(3)+1,J) ENDIF DO 450 JQ=1,2 IN(3+JQ)=IN(JQ) P(IN(JQ)+2,3)=P(IN(JQ)+2,3)-P(IN(JQ)+2,4) 450 P(IN(JQ)+2,1)=P(IN(JQ)+2,1)-(3-2*JQ)*P(IN(JQ)+2,4) GOTO 320 ENDIF C...Junction strings: save quantities left after each string. IF(IABS(KFL(1)).GT.10) GOTO 270 I=I-1 KFJH(IU)=KFL(1) DO 460 J=1,4 460 PJU(IU+3,J)=PJU(IU+3,J)-P(I+1,J) 470 CONTINUE C...Junction strings: put together to new effective string endpoint. NJS(JT)=I-ISTA KFJS(JT)=K(K(MJU(JT+2),3),2) KFLS=2*INT(RLU_HIJING(0)+3.*PARJ(4)/(1.+3.*PARJ(4)))+1 IF(KFJH(1).EQ.KFJH(2)) KFLS=3 IF(ISTA.NE.I) KFJS(JT)=ISIGN(1000*MAX(IABS(KFJH(1)), &IABS(KFJH(2)))+100*MIN(IABS(KFJH(1)),IABS(KFJH(2)))+ &KFLS,KFJH(1)) DO 480 J=1,4 PJS(JT,J)=PJU(1,J)+PJU(2,J)+P(MJU(JT),J) 480 PJS(JT+2,J)=PJU(4,J)+PJU(5,J) PJS(JT,5)=SQRT(MAX(0.,PJS(JT,4)**2-PJS(JT,1)**2-PJS(JT,2)**2- &PJS(JT,3)**2)) 490 CONTINUE C...Open versus closed strings. Choose breakup region for latter. 500 IF(MJU(1).NE.0.AND.MJU(2).NE.0) THEN NS=MJU(2)-MJU(1) NB=MJU(1)-N ELSEIF(MJU(1).NE.0) THEN NS=N+NR-MJU(1) NB=MJU(1)-N ELSEIF(MJU(2).NE.0) THEN NS=MJU(2)-N NB=1 ELSEIF(IABS(K(N+1,2)).NE.21) THEN NS=NR-1 NB=1 ELSE NS=NR+1 W2SUM=0. DO 510 IS=1,NR P(N+NR+IS,1)=0.5*FOUR(N+IS,N+IS+1-NR*(IS/NR)) 510 W2SUM=W2SUM+P(N+NR+IS,1) W2RAN=RLU_HIJING(0)*W2SUM NB=0 520 NB=NB+1 W2SUM=W2SUM-P(N+NR+NB,1) IF(W2SUM.GT.W2RAN.AND.NB.LT.NR) GOTO 520 ENDIF C...Find longitudinal string directions (i.e. lightlike four-vectors). DO 540 IS=1,NS IS1=N+IS+NB-1-NR*((IS+NB-2)/NR) IS2=N+IS+NB-NR*((IS+NB-1)/NR) DO 530 J=1,5 DP(1,J)=P(IS1,J) IF(IABS(K(IS1,2)).EQ.21) DP(1,J)=0.5*DP(1,J) IF(IS1.EQ.MJU(1)) DP(1,J)=PJS(1,J)-PJS(3,J) DP(2,J)=P(IS2,J) IF(IABS(K(IS2,2)).EQ.21) DP(2,J)=0.5*DP(2,J) 530 IF(IS2.EQ.MJU(2)) DP(2,J)=PJS(2,J)-PJS(4,J) DP(3,5)=DFOUR(1,1) DP(4,5)=DFOUR(2,2) DHKC=DFOUR(1,2) IF(DP(3,5)+2.*DHKC+DP(4,5).LE.0.) THEN DP(3,5)=DP(1,5)**2 DP(4,5)=DP(2,5)**2 DP(1,4)=SQRT(DP(1,1)**2+DP(1,2)**2+DP(1,3)**2+DP(1,5)**2) DP(2,4)=SQRT(DP(2,1)**2+DP(2,2)**2+DP(2,3)**2+DP(2,5)**2) DHKC=DFOUR(1,2) ENDIF DHKS=SQRT(DHKC**2-DP(3,5)*DP(4,5)) DHK1=0.5*((DP(4,5)+DHKC)/DHKS-1.) DHK2=0.5*((DP(3,5)+DHKC)/DHKS-1.) IN1=N+NR+4*IS-3 P(IN1,5)=SQRT(DP(3,5)+2.*DHKC+DP(4,5)) DO 540 J=1,4 P(IN1,J)=(1.+DHK1)*DP(1,J)-DHK2*DP(2,J) 540 P(IN1+1,J)=(1.+DHK2)*DP(2,J)-DHK1*DP(1,J) C...Begin initialization: sum up energy, set starting position. ISAV=I 550 NTRY=NTRY+1 IF(NTRY.GT.100.AND.NTRYR.LE.4) THEN PARU12=4.*PARU12 PARU13=2.*PARU13 GOTO 130 ELSEIF(NTRY.GT.100) THEN CALL LUERRM_HIJING(14 $ ,'(LUSTRF_HIJING:) caught in infinite loop') IF(MSTU(21).GE.1) RETURN ENDIF I=ISAV DO 560 J=1,4 P(N+NRS,J)=0. DO 560 IS=1,NR 560 P(N+NRS,J)=P(N+NRS,J)+P(N+IS,J) DO 570 JT=1,2 IRANK(JT)=0 IF(MJU(JT).NE.0) IRANK(JT)=NJS(JT) IF(NS.GT.NR) IRANK(JT)=1 IE(JT)=K(N+1+(JT/2)*(NP-1),3) IN(3*JT+1)=N+NR+1+4*(JT/2)*(NS-1) IN(3*JT+2)=IN(3*JT+1)+1 IN(3*JT+3)=N+NR+4*NS+2*JT-1 DO 570 IN1=N+NR+2+JT,N+NR+4*NS-2+JT,4 P(IN1,1)=2-JT P(IN1,2)=JT-1 570 P(IN1,3)=1. C...Initialize flavour and pT variables for open string. IF(NS.LT.NR) THEN PX(1)=0. PY(1)=0. IF(NS.EQ.1.AND.MJU(1)+MJU(2).EQ.0) CALL LUPTDI_HIJING(0,PX(1) $ ,PY(1)) PX(2)=-PX(1) PY(2)=-PY(1) DO 580 JT=1,2 KFL(JT)=K(IE(JT),2) IF(MJU(JT).NE.0) KFL(JT)=KFJS(JT) MSTJ(93)=1 PMQ(JT)=ULMASS_HIJING(KFL(JT)) 580 GAM(JT)=0. C...Closed string: random initial breakup flavour, pT and vertex. ELSE KFL(3)=INT(1.+(2.+PARJ(2))*RLU_HIJING(0))*(-1) $ **INT(RLU_HIJING(0)+0.5) CALL LUKFDI_HIJING(KFL(3),0,KFL(1),KDUMP) KFL(2)=-KFL(1) IF(IABS(KFL(1)).GT.10.AND.RLU_HIJING(0).GT.0.5) THEN KFL(2)=-(KFL(1)+ISIGN(10000,KFL(1))) ELSEIF(IABS(KFL(1)).GT.10) THEN KFL(1)=-(KFL(2)+ISIGN(10000,KFL(2))) ENDIF CALL LUPTDI_HIJING(KFL(1),PX(1),PY(1)) PX(2)=-PX(1) PY(2)=-PY(1) PR3=MIN(25.,0.1*P(N+NR+1,5)**2) 590 CALL LUZDIS_HIJING(KFL(1),KFL(2),PR3,Z) ZR=PR3/(Z*P(N+NR+1,5)**2) IF(ZR.GE.1.) GOTO 590 DO 600 JT=1,2 MSTJ(93)=1 PMQ(JT)=ULMASS_HIJING(KFL(JT)) GAM(JT)=PR3*(1.-Z)/Z IN1=N+NR+3+4*(JT/2)*(NS-1) P(IN1,JT)=1.-Z P(IN1,3-JT)=JT-1 P(IN1,3)=(2-JT)*(1.-Z)+(JT-1)*Z P(IN1+1,JT)=ZR P(IN1+1,3-JT)=2-JT 600 P(IN1+1,3)=(2-JT)*(1.-ZR)+(JT-1)*ZR ENDIF C...Find initial transverse directions (i.e. spacelike four-vectors). DO 640 JT=1,2 IF(JT.EQ.1.OR.NS.EQ.NR-1) THEN IN1=IN(3*JT+1) IN3=IN(3*JT+3) DO 610 J=1,4 DP(1,J)=P(IN1,J) DP(2,J)=P(IN1+1,J) DP(3,J)=0. 610 DP(4,J)=0. DP(1,4)=SQRT(DP(1,1)**2+DP(1,2)**2+DP(1,3)**2) DP(2,4)=SQRT(DP(2,1)**2+DP(2,2)**2+DP(2,3)**2) DP(5,1)=DP(1,1)/DP(1,4)-DP(2,1)/DP(2,4) DP(5,2)=DP(1,2)/DP(1,4)-DP(2,2)/DP(2,4) DP(5,3)=DP(1,3)/DP(1,4)-DP(2,3)/DP(2,4) IF(DP(5,1)**2.LE.DP(5,2)**2+DP(5,3)**2) DP(3,1)=1. IF(DP(5,1)**2.GT.DP(5,2)**2+DP(5,3)**2) DP(3,3)=1. IF(DP(5,2)**2.LE.DP(5,1)**2+DP(5,3)**2) DP(4,2)=1. IF(DP(5,2)**2.GT.DP(5,1)**2+DP(5,3)**2) DP(4,3)=1. DHC12=DFOUR(1,2) DHCX1=DFOUR(3,1)/DHC12 DHCX2=DFOUR(3,2)/DHC12 DHCXX=1D0/SQRT(1D0+2D0*DHCX1*DHCX2*DHC12) DHCY1=DFOUR(4,1)/DHC12 DHCY2=DFOUR(4,2)/DHC12 DHCYX=DHCXX*(DHCX1*DHCY2+DHCX2*DHCY1)*DHC12 DHCYY=1D0/SQRT(1D0+2D0*DHCY1*DHCY2*DHC12-DHCYX**2) DO 620 J=1,4 DP(3,J)=DHCXX*(DP(3,J)-DHCX2*DP(1,J)-DHCX1*DP(2,J)) P(IN3,J)=DP(3,J) 620 P(IN3+1,J)=DHCYY*(DP(4,J)-DHCY2*DP(1,J)-DHCY1*DP(2,J)- & DHCYX*DP(3,J)) ELSE DO 630 J=1,4 P(IN3+2,J)=P(IN3,J) 630 P(IN3+3,J)=P(IN3+1,J) ENDIF 640 CONTINUE C...Remove energy used up in junction string fragmentation. IF(MJU(1)+MJU(2).GT.0) THEN DO 660 JT=1,2 IF(NJS(JT).EQ.0) GOTO 660 DO 650 J=1,4 650 P(N+NRS,J)=P(N+NRS,J)-PJS(JT+2,J) 660 CONTINUE ENDIF C...Produce new particle: side, origin. 670 I=I+1 IF(2*I-NSAV.GE.MSTU(4)-MSTU(32)-5) THEN CALL LUERRM_HIJING(11 $ ,'(LUSTRF_HIJING:) no more memory left in LUJETS_HIJING') IF(MSTU(21).GE.1) RETURN ENDIF JT=1.5+RLU_HIJING(0) IF(IABS(KFL(3-JT)).GT.10) JT=3-JT JR=3-JT JS=3-2*JT IRANK(JT)=IRANK(JT)+1 K(I,1)=1 K(I,3)=IE(JT) K(I,4)=0 K(I,5)=0 C...Generate flavour, hadron and pT. 680 CALL LUKFDI_HIJING(KFL(JT),0,KFL(3),K(I,2)) IF(K(I,2).EQ.0) GOTO 550 IF(MSTJ(12).GE.3.AND.IRANK(JT).EQ.1.AND.IABS(KFL(JT)).LE.10.AND. &IABS(KFL(3)).GT.10) THEN IF(RLU_HIJING(0).GT.PARJ(19)) GOTO 680 ENDIF P(I,5)=ULMASS_HIJING(K(I,2)) CALL LUPTDI_HIJING(KFL(JT),PX(3),PY(3)) PR(JT)=P(I,5)**2+(PX(JT)+PX(3))**2+(PY(JT)+PY(3))**2 C...Final hadrons for small invariant mass. MSTJ(93)=1 PMQ(3)=ULMASS_HIJING(KFL(3)) WMIN=PARJ(32+MSTJ(11))+PMQ(1)+PMQ(2)+PARJ(36)*PMQ(3) IF(IABS(KFL(JT)).GT.10.AND.IABS(KFL(3)).GT.10) WMIN= &WMIN-0.5*PARJ(36)*PMQ(3) WREM2=FOUR(N+NRS,N+NRS) IF(WREM2.LT.0.10) GOTO 550 IF(WREM2.LT.MAX(WMIN*(1.+(2.*RLU_HIJING(0)-1.)*PARJ(37)), &PARJ(32)+PMQ(1)+PMQ(2))**2) GOTO 810 C...Choose z, which gives Gamma. Shift z for heavy flavours. CALL LUZDIS_HIJING(KFL(JT),KFL(3),PR(JT),Z) KFL1A=IABS(KFL(1)) KFL2A=IABS(KFL(2)) IF(MAX(MOD(KFL1A,10),MOD(KFL1A/1000,10),MOD(KFL2A,10), &MOD(KFL2A/1000,10)).GE.4) THEN PR(JR)=(PMQ(JR)+PMQ(3))**2+(PX(JR)-PX(3))**2+(PY(JR)-PY(3))**2 PW12=SQRT(MAX(0.,(WREM2-PR(1)-PR(2))**2-4.*PR(1)*PR(2))) Z=(WREM2+PR(JT)-PR(JR)+PW12*(2.*Z-1.))/(2.*WREM2) PR(JR)=(PMQ(JR)+PARJ(32+MSTJ(11)))**2+(PX(JR)-PX(3))**2+ & (PY(JR)-PY(3))**2 IF((1.-Z)*(WREM2-PR(JT)/Z).LT.PR(JR)) GOTO 810 ENDIF GAM(3)=(1.-Z)*(GAM(JT)+PR(JT)/Z) DO 690 J=1,3 690 IN(J)=IN(3*JT+J) C...Stepping within or from 'low' string region easy. IF(IN(1)+1.EQ.IN(2).AND.Z*P(IN(1)+2,3)*P(IN(2)+2,3)* &P(IN(1),5)**2.GE.PR(JT)) THEN P(IN(JT)+2,4)=Z*P(IN(JT)+2,3) P(IN(JR)+2,4)=PR(JT)/(P(IN(JT)+2,4)*P(IN(1),5)**2) DO 700 J=1,4 700 P(I,J)=(PX(JT)+PX(3))*P(IN(3),J)+(PY(JT)+PY(3))*P(IN(3)+1,J) GOTO 770 ELSEIF(IN(1)+1.EQ.IN(2)) THEN P(IN(JR)+2,4)=P(IN(JR)+2,3) P(IN(JR)+2,JT)=1. IN(JR)=IN(JR)+4*JS IF(JS*IN(JR).GT.JS*IN(4*JR)) GOTO 550 IF(FOUR(IN(1),IN(2)).LE.1E-2) THEN P(IN(JT)+2,4)=P(IN(JT)+2,3) P(IN(JT)+2,JT)=0. IN(JT)=IN(JT)+4*JS ENDIF ENDIF C...Find new transverse directions (i.e. spacelike string vectors). 710 IF(JS*IN(1).GT.JS*IN(3*JR+1).OR.JS*IN(2).GT.JS*IN(3*JR+2).OR. &IN(1).GT.IN(2)) GOTO 550 IF(IN(1).NE.IN(3*JT+1).OR.IN(2).NE.IN(3*JT+2)) THEN DO 720 J=1,4 DP(1,J)=P(IN(1),J) DP(2,J)=P(IN(2),J) DP(3,J)=0. 720 DP(4,J)=0. DP(1,4)=SQRT(DP(1,1)**2+DP(1,2)**2+DP(1,3)**2) DP(2,4)=SQRT(DP(2,1)**2+DP(2,2)**2+DP(2,3)**2) DHC12=DFOUR(1,2) IF(DHC12.LE.1E-2) THEN P(IN(JT)+2,4)=P(IN(JT)+2,3) P(IN(JT)+2,JT)=0. IN(JT)=IN(JT)+4*JS GOTO 710 ENDIF IN(3)=N+NR+4*NS+5 DP(5,1)=DP(1,1)/DP(1,4)-DP(2,1)/DP(2,4) DP(5,2)=DP(1,2)/DP(1,4)-DP(2,2)/DP(2,4) DP(5,3)=DP(1,3)/DP(1,4)-DP(2,3)/DP(2,4) IF(DP(5,1)**2.LE.DP(5,2)**2+DP(5,3)**2) DP(3,1)=1. IF(DP(5,1)**2.GT.DP(5,2)**2+DP(5,3)**2) DP(3,3)=1. IF(DP(5,2)**2.LE.DP(5,1)**2+DP(5,3)**2) DP(4,2)=1. IF(DP(5,2)**2.GT.DP(5,1)**2+DP(5,3)**2) DP(4,3)=1. DHCX1=DFOUR(3,1)/DHC12 DHCX2=DFOUR(3,2)/DHC12 DHCXX=1D0/SQRT(1D0+2D0*DHCX1*DHCX2*DHC12) DHCY1=DFOUR(4,1)/DHC12 DHCY2=DFOUR(4,2)/DHC12 DHCYX=DHCXX*(DHCX1*DHCY2+DHCX2*DHCY1)*DHC12 DHCYY=1D0/SQRT(1D0+2D0*DHCY1*DHCY2*DHC12-DHCYX**2) DO 730 J=1,4 DP(3,J)=DHCXX*(DP(3,J)-DHCX2*DP(1,J)-DHCX1*DP(2,J)) P(IN(3),J)=DP(3,J) 730 P(IN(3)+1,J)=DHCYY*(DP(4,J)-DHCY2*DP(1,J)-DHCY1*DP(2,J)- & DHCYX*DP(3,J)) C...Express pT with respect to new axes, if sensible. PXP=-(PX(3)*FOUR(IN(3*JT+3),IN(3))+PY(3)* & FOUR(IN(3*JT+3)+1,IN(3))) PYP=-(PX(3)*FOUR(IN(3*JT+3),IN(3)+1)+PY(3)* & FOUR(IN(3*JT+3)+1,IN(3)+1)) IF(ABS(PXP**2+PYP**2-PX(3)**2-PY(3)**2).LT.0.01) THEN PX(3)=PXP PY(3)=PYP ENDIF ENDIF C...Sum up known four-momentum. Gives coefficients for m2 expression. DO 750 J=1,4 DHG(J)=0. P(I,J)=PX(JT)*P(IN(3*JT+3),J)+PY(JT)*P(IN(3*JT+3)+1,J)+ &PX(3)*P(IN(3),J)+PY(3)*P(IN(3)+1,J) DO 740 IN1=IN(3*JT+1),IN(1)-4*JS,4*JS 740 P(I,J)=P(I,J)+P(IN1+2,3)*P(IN1,J) DO 750 IN2=IN(3*JT+2),IN(2)-4*JS,4*JS 750 P(I,J)=P(I,J)+P(IN2+2,3)*P(IN2,J) DHM(1)=FOUR(I,I) DHM(2)=2.*FOUR(I,IN(1)) DHM(3)=2.*FOUR(I,IN(2)) DHM(4)=2.*FOUR(IN(1),IN(2)) C...Find coefficients for Gamma expression. DO 760 IN2=IN(1)+1,IN(2),4 DO 760 IN1=IN(1),IN2-1,4 DHC=2.*FOUR(IN1,IN2) DHG(1)=DHG(1)+P(IN1+2,JT)*P(IN2+2,JT)*DHC IF(IN1.EQ.IN(1)) DHG(2)=DHG(2)-JS*P(IN2+2,JT)*DHC IF(IN2.EQ.IN(2)) DHG(3)=DHG(3)+JS*P(IN1+2,JT)*DHC 760 IF(IN1.EQ.IN(1).AND.IN2.EQ.IN(2)) DHG(4)=DHG(4)-DHC C...Solve (m2, Gamma) equation system for energies taken. DHS1=DHM(JR+1)*DHG(4)-DHM(4)*DHG(JR+1) IF(ABS(DHS1).LT.1E-4) GOTO 550 DHS2=DHM(4)*(GAM(3)-DHG(1))-DHM(JT+1)*DHG(JR+1)-DHG(4)* &(P(I,5)**2-DHM(1))+DHG(JT+1)*DHM(JR+1) DHS3=DHM(JT+1)*(GAM(3)-DHG(1))-DHG(JT+1)*(P(I,5)**2-DHM(1)) P(IN(JR)+2,4)=0.5*(SQRT(MAX(0D0,DHS2**2-4.*DHS1*DHS3))/ABS(DHS1)- &DHS2/DHS1) IF(DHM(JT+1)+DHM(4)*P(IN(JR)+2,4).LE.0.) GOTO 550 P(IN(JT)+2,4)=(P(I,5)**2-DHM(1)-DHM(JR+1)*P(IN(JR)+2,4))/ &(DHM(JT+1)+DHM(4)*P(IN(JR)+2,4)) C...Step to new region if necessary. IF(P(IN(JR)+2,4).GT.P(IN(JR)+2,3)) THEN P(IN(JR)+2,4)=P(IN(JR)+2,3) P(IN(JR)+2,JT)=1. IN(JR)=IN(JR)+4*JS IF(JS*IN(JR).GT.JS*IN(4*JR)) GOTO 550 IF(FOUR(IN(1),IN(2)).LE.1E-2) THEN P(IN(JT)+2,4)=P(IN(JT)+2,3) P(IN(JT)+2,JT)=0. IN(JT)=IN(JT)+4*JS ENDIF GOTO 710 ELSEIF(P(IN(JT)+2,4).GT.P(IN(JT)+2,3)) THEN P(IN(JT)+2,4)=P(IN(JT)+2,3) P(IN(JT)+2,JT)=0. IN(JT)=IN(JT)+4*JS GOTO 710 ENDIF C...Four-momentum of particle. Remaining quantities. Loop back. 770 DO 780 J=1,4 P(I,J)=P(I,J)+P(IN(1)+2,4)*P(IN(1),J)+P(IN(2)+2,4)*P(IN(2),J) 780 P(N+NRS,J)=P(N+NRS,J)-P(I,J) IF(P(I,4).LE.0.) GOTO 550 KFL(JT)=-KFL(3) PMQ(JT)=PMQ(3) PX(JT)=-PX(3) PY(JT)=-PY(3) GAM(JT)=GAM(3) IF(IN(3).NE.IN(3*JT+3)) THEN DO 790 J=1,4 P(IN(3*JT+3),J)=P(IN(3),J) 790 P(IN(3*JT+3)+1,J)=P(IN(3)+1,J) ENDIF DO 800 JQ=1,2 IN(3*JT+JQ)=IN(JQ) P(IN(JQ)+2,3)=P(IN(JQ)+2,3)-P(IN(JQ)+2,4) 800 P(IN(JQ)+2,JT)=P(IN(JQ)+2,JT)-JS*(3-2*JQ)*P(IN(JQ)+2,4) GOTO 670 C...Final hadron: side, flavour, hadron, mass. 810 I=I+1 K(I,1)=1 K(I,3)=IE(JR) K(I,4)=0 K(I,5)=0 CALL LUKFDI_HIJING(KFL(JR),-KFL(3),KFLDMP,K(I,2)) IF(K(I,2).EQ.0) GOTO 550 P(I,5)=ULMASS_HIJING(K(I,2)) PR(JR)=P(I,5)**2+(PX(JR)-PX(3))**2+(PY(JR)-PY(3))**2 C...Final two hadrons: find common setup of four-vectors. JQ=1 IF(P(IN(4)+2,3)*P(IN(5)+2,3)*FOUR(IN(4),IN(5)).LT.P(IN(7),3)* &P(IN(8),3)*FOUR(IN(7),IN(8))) JQ=2 DHC12=FOUR(IN(3*JQ+1),IN(3*JQ+2)) DHR1=FOUR(N+NRS,IN(3*JQ+2))/DHC12 DHR2=FOUR(N+NRS,IN(3*JQ+1))/DHC12 IF(IN(4).NE.IN(7).OR.IN(5).NE.IN(8)) THEN PX(3-JQ)=-FOUR(N+NRS,IN(3*JQ+3))-PX(JQ) PY(3-JQ)=-FOUR(N+NRS,IN(3*JQ+3)+1)-PY(JQ) PR(3-JQ)=P(I+(JT+JQ-3)**2-1,5)**2+(PX(3-JQ)+(2*JQ-3)*JS* & PX(3))**2+(PY(3-JQ)+(2*JQ-3)*JS*PY(3))**2 ENDIF C...Solve kinematics for final two hadrons, if possible. WREM2=WREM2+(PX(1)+PX(2))**2+(PY(1)+PY(2))**2 FD=(SQRT(PR(1))+SQRT(PR(2)))/SQRT(WREM2) IF(MJU(1)+MJU(2).NE.0.AND.I.EQ.ISAV+2.AND.FD.GE.1.) GOTO 180 IF(FD.GE.1.) GOTO 550 FA=WREM2+PR(JT)-PR(JR) IF(MSTJ(11).EQ.2) PREV=0.5*FD**PARJ(37+MSTJ(11)) IF(MSTJ(11).NE.2) PREV=0.5*EXP(MAX(-100.,LOG(FD)* &PARJ(37+MSTJ(11))*(PR(1)+PR(2))**2)) FB=SIGN(SQRT(MAX(0.,FA**2-4.*WREM2*PR(JT))),JS*(RLU_HIJING(0)-PREV $ )) KFL1A=IABS(KFL(1)) KFL2A=IABS(KFL(2)) IF(MAX(MOD(KFL1A,10),MOD(KFL1A/1000,10),MOD(KFL2A,10), &MOD(KFL2A/1000,10)).GE.6) FB=SIGN(SQRT(MAX(0.,FA**2- &4.*WREM2*PR(JT))),FLOAT(JS)) DO 820 J=1,4 P(I-1,J)=(PX(JT)+PX(3))*P(IN(3*JQ+3),J)+(PY(JT)+PY(3))* &P(IN(3*JQ+3)+1,J)+0.5*(DHR1*(FA+FB)*P(IN(3*JQ+1),J)+ &DHR2*(FA-FB)*P(IN(3*JQ+2),J))/WREM2 820 P(I,J)=P(N+NRS,J)-P(I-1,J) C...Mark jets as fragmented and give daughter pointers. N=I-NRS+1 DO 830 I=NSAV+1,NSAV+NP IM=K(I,3) K(IM,1)=K(IM,1)+10 IF(MSTU(16).NE.2) THEN K(IM,4)=NSAV+1 K(IM,5)=NSAV+1 ELSE K(IM,4)=NSAV+2 K(IM,5)=N ENDIF 830 CONTINUE C...Document string system. Move up particles. NSAV=NSAV+1 K(NSAV,1)=11 K(NSAV,2)=92 K(NSAV,3)=IP K(NSAV,4)=NSAV+1 K(NSAV,5)=N DO 840 J=1,4 P(NSAV,J)=DPS(J) 840 V(NSAV,J)=V(IP,J) P(NSAV,5)=SQRT(MAX(0D0,DPS(4)**2-DPS(1)**2-DPS(2)**2-DPS(3)**2)) V(NSAV,5)=0. DO 850 I=NSAV+1,N DO 850 J=1,5 K(I,J)=K(I+NRS-1,J) P(I,J)=P(I+NRS-1,J) 850 V(I,J)=0. C...Order particles in rank along the chain. Update mother pointer. DO 860 I=NSAV+1,N DO 860 J=1,5 K(I-NSAV+N,J)=K(I,J) 860 P(I-NSAV+N,J)=P(I,J) I1=NSAV DO 880 I=N+1,2*N-NSAV IF(K(I,3).NE.IE(1)) GOTO 880 I1=I1+1 DO 870 J=1,5 K(I1,J)=K(I,J) 870 P(I1,J)=P(I,J) IF(MSTU(16).NE.2) K(I1,3)=NSAV 880 CONTINUE DO 900 I=2*N-NSAV,N+1,-1 IF(K(I,3).EQ.IE(1)) GOTO 900 I1=I1+1 DO 890 J=1,5 K(I1,J)=K(I,J) 890 P(I1,J)=P(I,J) IF(MSTU(16).NE.2) K(I1,3)=NSAV 900 CONTINUE C...Boost back particle system. Set production vertices. CALL LUDBRB_HIJING(NSAV+1,N,0.,0.,DPS(1)/DPS(4),DPS(2)/DPS(4), &DPS(3)/DPS(4)) DO 910 I=NSAV+1,N DO 910 J=1,4 910 V(I,J)=V(IP,J) RETURN END