mother daughter relations

[Sadia Khalil]

Dear all,

Is the class DelphesHepMCReader up to date w.r.t pythia8 parameters? Using the standard CMS configuration file (CMS_PhaseII_Substructure_200PU.tcl) to Delphes trees, and following the example Example5.C, I do not understand as how can I access the PDGID of mother and daughters of a particular decay, say top -> b W.

Thanks,
Sadia

[Pavel Demin]

As far as I know there is nothing Pythia8 specific in the HepMC file format. However, it's possible that when converting from the HepMC vertices to the M1/M2 and D1/D2 indices some of them aren't calculated correctly.

Could you please provide more details about your problem?

[Pavel Demin]

I've checked CMS_PhaseII_Substructure_200PU.tcl and I think that I've found the source of the problem. This card has the GenParticleFilter module enabled. This module removes some generated particles. In this case, the mother and daughter indices become unusable.

The easiest solution is to replace

add Branch GenParticleFilter/filteredParticles Particle GenParticle

with

add Branch Delphes/allParticles Particle GenParticle

If M2 (or D2) is -1, then M1 (or D1) is the index of the mother (daughter). Otherwise M1 (or D1) is the index of the first mother (or daughter) and M2 (or D2) is the index of the last mother.