multileptonic signature from ttbar

[luigidr]

Dear Delphes experts,

I'm interested in a 3 leptonic signature coming from a t tbar, where two leptons originate from the Ws decays (from t and anti-t) and a further lepton comes from a semi-leptonic B meson decay (from the b quark).
I simulate the process using MadGraph+Pythia+Delphes but I'm not able to find any multi-leptonic event in the root file generated by Delphes.
I've checked that these events are instead present in the .hep file generated by Pythia.
I've built my analysis code working on the Example1.C that you provide with the Delphes package and I've run Delphes, through the MadGraph interface, using the default Delphes card (which I have attached).

Could you please help me to understand this behaviour? Unfortunately my knowledge of the Delphes package is still not deep.

Many thanks,
Luigi

[luigidr]

delphes card

[Michele Selvaggi]

By default Delphes will produce isolated objects. Muons originating from semi-leptonic B decays are typically not isolated.
To relax the isolation criterion you can:

set PTRatioMax 9999

in the MuonIsolation section of the card. At the analysis level you can then select two isolated muons (by requiring the !Isolationvar < 0.1)

[luigidr]

Thanks very much!
From the physical point of view, could I relax the isolation criterion also for electrons? Concerning the isolation, do they behave as the muons?
Thanks,
Luigi

[Michele Selvaggi]

Usually one sets tighter isolation criteria for electrons, because they have higher chance of being due to fake. I would use 0.2 for muons and 0.1 for electrons as a starting point.

[luigidr]

Thanks a lot!