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- void DecayConfig() {
-
- // This script uses the external decayer TPythia6Decayer in place of the
- // concrete Monte Carlo native decay mechanisms only for the
- // specific types of decays defined below.
-
- // Access the external decayer singleton and initialize it
- TPythia6Decayer* decayer = TPythia6Decayer::Instance();
- // The following just tells pythia6 to not decay particles only to
- // certain channels.
-
- decayer->SetForceDecay(TPythia6Decayer::kAll);
- //example: Force the J/PSI decay channel e+e-
- // Int_t products[2];
- // Int_t mult[2];
- // Int_t npart=2;
- //decay products
- // products[0]=11;
- // products[1]=-11;
- //multiplicity
- // mult[0]=1;
- // mult[1]=1;
- // force the decay channel
- // decayer->ForceParticleDecay(443,products,mult,npart);
- decayer->Init();
-
- // Tell the concrete monte carlo to use the external decayer. The
- // external decayer will be used for:
- // i)particle decays not defined in concrete monte carlo, or
- //ii)particles for which the concrete monte carlo is told
- // to use the external decayer for its type via:
- // gMC->SetUserDecay(pdgId);
- // If this is invoked, the external decayer will be used for particles
- // of type pdgId even if the concrete monte carlo has a decay mode
- // already defined for that particle type.
- gMC->SetExternalDecayer(decayer);
-
- TPythia6& pythia6 = *(TPythia6::Instance());
-
- // The pythia6 decayer is used in place of the concrete Monte Carlo
- // decay for the particles type mu+/-,pi+/-, K+/-, K0L in order to preserve
- // the decay product neutrino flavor, which is otherwise not preserved in
- // Geant3 decays.
- const Int_t npartnf = 9;
- // mu-,mu+,pi+,pi-,K+,K-,K0L, Xi-
- Int_t pdgnf[npartnf] = {13,-13,211,-211,321,-321,130, 3312, 443};
- for ( Int_t ipartnf = 0; ipartnf < npartnf; ipartnf++ ) {
- Int_t ipdg = pdgnf[ipartnf];
-
- if (TString(gMC->GetName()) == "TGeant3") gMC->SetUserDecay(ipdg);// Force the decay to be done w/external decayer
-
- pythia6.SetMDCY(pythia6.Pycomp(ipdg),1,1); // Activate decay in pythia
- }
-
-
- // The following will print the decay modes
- pythia6.Pyupda(1,6);
-
- // rho0 (113), rho+ (213), rho- (-213) and
- // D+(411) ,D-(-411),D0(421),D0bar(-421) have decay modes defined in
- // TGeant3::DefineParticles, but for these particles
- // those decay modes are overridden to make use of pythia6.
- const Int_t nparthq = 3;
- // rho0,rho+,rho-,D+,D-,D0,D0bar
- //Int_t pdghq[nparthq] = {113,213,-213,411,-411,421,-421};
- Int_t pdghq[nparthq] = {421,3122,-3122};
- for ( Int_t iparthq = 0; iparthq < nparthq; iparthq++ ) {
- Int_t ipdg = pdghq[iparthq];
- if (TString(gMC->GetName()) == "TGeant3") gMC->SetUserDecay(ipdg); // Force the decay to be done w/external decayer
- pythia6.SetMDCY(pythia6.Pycomp(ipdg),1,1); // Activate decay in pythia
- }
- // Set pi0 to be stable in pythia6 so that Geant3 can handle decay.
- // In general, TGeant3 is set up through TGeant3gu::gudcay to pass
- // all pythia6 decay products back to the G3 transport mechanism if they
- // have a lifetime > 1.E-15 sec for further transport.
- // Since the pi0 lifetime is less than this, if pi0 is produced as a decay
- // product in pythia6, e.g. KL0 -> pi0 pi+ pi-, the pi0 will be immediately
- // decayed by pythia6 to 2 gammas, and the KL0 decay product list passed
- // back to the transport mechanism will be "gamma gamma pi+ pi-", i.e.
- // the pi0 will not be visible in the list of secondaries passed back to
- // the transport mechanism and will not be pushed to the stack for possible
- // storage to the stdhep output array.
- // To avoid this, the pi0 is set to stable in pythia6, and its decay
- // will be handled by Geant3.
- //pythia6.SetMDCY(pythia6.Pycomp(111),1,0);
- //}
- }
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