C...Interface from 4-fermion generator at LEP 2 to Jetset showers and C...fragmentation. C...First comes very stupid main program to test interface below. PARAMETER (NMXHEP=2000) COMMON/HEPEVT/NEVHEP,NHEP,ISTHEP(NMXHEP),IDHEP(NMXHEP), &JMOHEP(2,NMXHEP),JDAHEP(2,NMXHEP),PHEP(5,NMXHEP),VHEP(4,NMXHEP) DOUBLE PRECISION PHEP, VHEP COMMON/LUDAT3/MDCY(500,3),MDME(2000,2),BRAT(2000),KFDP(2000,5) C...Loop over events. Decide how many entries. Reset. DO 200 IEV=1,1000 NEVHEP=IEV NHEP=6+INT(4.*RLU(0)) DO 110 I=1,NHEP ISTHEP(I)=1 IDHEP(I)=22 JMOHEP(1,I)=0 JMOHEP(2,I)=0 JDAHEP(1,I)=0 JDAHEP(2,I)=0 DO 100 J=1,5 100 PHEP(J,I)=0. DO 110 J=1,4 110 VHEP(J,I)=0. C...Generate flavours at random. ISTHEP(1)=3 IDHEP(1)=-11 ISTHEP(2)=3 IDHEP(2)=11 DO 120 IDL=MDCY(24,2),MDCY(24,2)+MDCY(24,3)-1 BRSU=BRSU+BRAT(IDL) 120 CONTINUE DO 150 I=3,5,2 130 RBR=BRSU*RLU(0) IDL=MDCY(24,2)-1 140 IDL=IDL+1 IDC=IDL RBR=RBR-BRAT(IDL) IF(IDL.LT.MDCY(24,2)+MDCY(24,3)-1.AND.RBR.GT.0.) GOTO 140 IF(I.EQ.3) THEN IDHEP(I)=KFDP(IDC,2) IDHEP(I+1)=KFDP(IDC,1) ELSE IDHEP(I)=-KFDP(IDC,1) IDHEP(I+1)=-KFDP(IDC,2) ENDIF PHEP(5,I)=ULMASS(IDHEP(I)) PHEP(5,I+1)=ULMASS(IDHEP(I+1)) IF(PHEP(5,I)+PHEP(5,I+1).GT.20.) GOTO 130 150 CONTINUE C...Generate momenta at random. DO 160 I=3,NHEP PLEN=50. IF(I.GE.5) PLEN=5. PHEP(1,I)=PLEN*(2.*RLU(0)-1.) PHEP(2,I)=PLEN*(2.*RLU(0)-1.) PHEP(3,I)=PLEN*(2.*RLU(0)-1.) 160 PHEP(4,I)=SQRT(PHEP(1,I)**2+PHEP(2,I)**2+PHEP(3,I)**2+ &PHEP(5,I)**2) C....Call interface to JETSET. List generated event. IERR=0 CALL LU4FRM(1.,0.5,0.5,2,0,0,IERR) IF(IEV.LE.10) CALL LULIST(1) 200 CONTINUE END C******************************************************************* C...The following subroutine illustrates how to write a generic C...interface between electroweak generators and QCD generators C...for LEP 2 applications. C... C...In this particular case, an electroweak generator is supposed to C...have produced two fermions, two antifermions and an arbitrary C...number of photons. These particles are stored in the HEPEVT C...common block. The allowed order is specified by a standard. C...In brief, the final fermions should appear in the order C...fermion (1) - antifermion (2) - fermion (3) - antifermion (4). C...The flavour pairs should be arranged so that, if possible, the C...first two could come from a W+ and the second two from a W-; C...else each pair should have flavours consistent with a Z0. C...The subroutine LU4FRM is supposed to read the configuration, C...and call JETSET to do parton showers and fragmentation. C... C...Since the colour flow need not be unique, three real numbers C...should be given when LU4FRM is called: C...ATOTSQ = total squared amplitude for the event, irrespective of C... colour flow; C...A1SQ = squared amplitude for the configuration with 1 + 2 and C... 3 + 4 as the two colour singlets; and C...A2SQ = squared amplitude for the configuration with 1 + 4 and C... 3 + 2 as the two colour singlets. C... C...The choice of strategy is determined by an integer input: C...ISTRAT = 0 : pick configurations according to A1SQ : A2SQ; C... = 1 : assign interference to maximize 1 + 2 and 3 + 4; or C... = 2 : assign interference to maximize 1 + 4 and 3 + 2. C... C...Final-state QED radiation may be allowed or inhibited: C...IRAD = 0 : no final-state photon radiation. C... = 1 : photon radiation inside each final fermion pair. C... C...tau lepton decay may be handled by QCD generator or not. C...ITAU = 0 : taus are considered stable by QCD generator. C... = 1 : taus are allowed to decay by QCD generator. C... C...IERR is an error flag, used both as input and output. C...At input, 0 means leave routine in case of error, C... nonzero means stop program execution. C...At output, 0 means acceptable fermion configuration, C... nonzero means treatment aborted for some reason. C...It is up to the writer of the main program to pick error strategy, C...i.e. to let the program crash or try to fix errors. C...Program changed 20 December 1996: add QED radiation off C...lepton-neutrino pair for IRAD=1; previously IRAD=1 only C...affected photon radiation off quark-antiquark. C...Program changed 6 August 1998: tau's that had radiated photons C...were not correctly picked up and forbidden to decay in the C...ITAU=0 option. SUBROUTINE LU4FRM(ATOTSQ,A1SQ,A2SQ,ISTRAT,IRAD,ITAU,IERR) COMMON/LUJETS/N,K(4000,5),P(4000,5),V(4000,5) COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200) DIMENSION IJOIN(2),INTAU(4) C...Call LUHEPC to convert from HEPEVT to LUJETS common. INERR=0 MSTU(28)=0 CALL LUHEPC(2) IF(MSTU(28).EQ.8) INERR=1 C...Loop through entries and pick up all final fermions/antifermions. I1=0 I2=0 I3=0 I4=0 DO 100 I=1,N IF(K(I,1).LE.0.OR.K(I,1).GT.10) GOTO 100 KFA=IABS(K(I,2)) IF((KFA.GE.1.AND.KFA.LE.6).OR.(KFA.GE.11.AND.KFA.LE.16)) THEN IF(K(I,2).GT.0) THEN IF(I1.EQ.0) THEN I1=I ELSEIF(I3.EQ.0) THEN I3=I ELSE INERR=2 CALL LUERRM(6,'(LU4FRM:) more than two fermions') ENDIF ELSE IF(I2.EQ.0) THEN I2=I ELSEIF(I4.EQ.0) THEN I4=I ELSE INERR=3 CALL LUERRM(6,'(LU4FRM:) more than two antifermions') ENDIF ENDIF ENDIF 100 CONTINUE C...Check that event is arranged according to conventions. IF(I1.EQ.0.OR.I2.EQ.0.OR.I3.EQ.0.OR.I4.EQ.0) THEN INERR=4 CALL LUERRM(6,'(LU4FRM:) event contains too few fermions') ENDIF IF(I2.LT.I1.OR.I3.LT.I2.OR.I4.LT.I3) THEN INERR=5 CALL LUERRM(6,'(LU4FRM:) fermions arranged in wrong order') ENDIF C...Check which fermion pairs are quarks and which leptons. IF(IABS(K(I1,2)).LT.10.AND.IABS(K(I2,2)).LT.10) THEN IQL12=1 ELSEIF(IABS(K(I1,2)).GT.10.AND.IABS(K(I2,2)).GT.10) THEN IQL12=2 ELSE INERR=6 CALL LUERRM(6,'(LU4FRM:) first fermion pair inconsistent') ENDIF IF(IABS(K(I3,2)).LT.10.AND.IABS(K(I4,2)).LT.10) THEN IQL34=1 ELSEIF(IABS(K(I3,2)).GT.10.AND.IABS(K(I4,2)).GT.10) THEN IQL34=2 ELSE INERR=7 CALL LUERRM(6,'(LU4FRM:) second fermion pair inconsistent') ENDIF C...Return or stop program in case of problems. IF(INERR.EQ.0) THEN IERR=0 ELSEIF(IERR.EQ.0) THEN IERR=INERR RETURN ELSE WRITE(6,*) ' ERROR: listing of faulty event follows:' CALL LULIST(2) WRITE(6,*) ' Fermions found in lines ',I1,I2,I3,I4 WRITE(6,*) ' Error type in event above is ',INERR WRITE(6,*) ' Program execution will be stopped now' WRITE(6,*) ' since main program does not correct errors!' STOP ENDIF C...Decide whether to allow or not photon radiation in showers. MSTJ(41)=2 IF(IRAD.EQ.0) MSTJ(41)=1 C...Decide on colour pairing. IF(IQL12.EQ.2.AND.IQL34.EQ.2) THEN NPAIR=0 ELSEIF(IQL12.EQ.1.AND.IQL34.EQ.2) THEN NPAIR=1 IP1=I1 IP2=I2 ELSEIF(IQL12.EQ.2.AND.IQL34.EQ.1) THEN NPAIR=1 IP1=I3 IP2=I4 ELSE NPAIR=2 IP1=I1 IP3=I3 R1SQ=A1SQ R2SQ=A2SQ DELTA=ATOTSQ-A1SQ-A2SQ IF(ISTRAT.EQ.1) THEN IF(DELTA.GT.0.) R1SQ=R1SQ+DELTA IF(DELTA.LT.0.) R2SQ=MAX(0.,R2SQ+DELTA) ELSEIF(ISTRAT.EQ.2) THEN IF(DELTA.GT.0.) R2SQ=R2SQ+DELTA IF(DELTA.LT.0.) R1SQ=MAX(0.,R1SQ+DELTA) ENDIF IF(R2SQ.LT.RLU(0)*(R1SQ+R2SQ)) THEN IP2=I2 IP4=I4 ELSE IP2=I4 IP4=I2 ENDIF ENDIF C...Do colour joining and parton showers. IF(NPAIR.GE.1) THEN IJOIN(1)=IP1 IJOIN(2)=IP2 CALL LUJOIN(2,IJOIN) PM12S=(P(IP1,4)+P(IP2,4))**2-(P(IP1,1)+P(IP2,1))**2- & (P(IP1,2)+P(IP2,2))**2-(P(IP1,3)+P(IP2,3))**2 CALL LUSHOW(IP1,IP2,SQRT(MAX(0.,PM12S))) ENDIF IF(NPAIR.EQ.2) THEN IJOIN(1)=IP3 IJOIN(2)=IP4 CALL LUJOIN(2,IJOIN) PM34S=(P(IP3,4)+P(IP4,4))**2-(P(IP3,1)+P(IP4,1))**2- & (P(IP3,2)+P(IP4,2))**2-(P(IP3,3)+P(IP4,3))**2 CALL LUSHOW(IP3,IP4,SQRT(MAX(0.,PM34S))) ENDIF C...Do optional QED showers for lepton/neutrino pairs. C...(Inserted 20 December 1996.) IF(IRAD.EQ.1) THEN IF(IQL12.EQ.2) THEN PM12S=(P(I1,4)+P(I2,4))**2-(P(I1,1)+P(I2,1))**2- & (P(I1,2)+P(I2,2))**2-(P(I1,3)+P(I2,3))**2 CALL LUSHOW(I1,I2,SQRT(MAX(0.,PM12S))) ENDIF IF(IQL34.EQ.2) THEN PM34S=(P(I3,4)+P(I4,4))**2-(P(I3,1)+P(I4,1))**2- & (P(I3,2)+P(I4,2))**2-(P(I3,3)+P(I4,3))**2 CALL LUSHOW(I3,I4,SQRT(MAX(0.,PM34S))) ENDIF ENDIF C...Do fragmentation and decays. Possibly except tau decay. C...(Modified 6 August 1998.) IF(ITAU.EQ.0) THEN NTAU=0 DO 110 I=1,N IF(IABS(K(I,2)).EQ.15.AND.K(I,1).EQ.1) THEN NTAU=NTAU+1 INTAU(NTAU)=I K(I,1)=11 ENDIF 110 CONTINUE ENDIF CALL LUEXEC IF(ITAU.EQ.0) THEN DO 120 I=1,NTAU K(INTAU(I),1)=1 120 CONTINUE ENDIF END