Muon Displacement Not Simulated Properly
Dear MG5 experts,
I was recently checking the simulation of the events from the LHE file [1] produced from MadGraph5. In each event, we have two light boson (PDG ID =3000022) each decays to a pair of oppositely charged muons. We also manually added lifetime (using a python script and change the lifetime column) for the boson in the LHE events so that it can travel some distance before decaying to muons. In such cases, the muons are expected to be displaced from the interaction point/ beam line.
We simulate the events all the way to the event reconstruction in the CMS detector. From the CMS event display in [2], I can see the GEN level muons are displaced as expected (The white curves in the main RhoPhi view). But things are a bit more complicated for the reconstructed muons (red curves). In this specific event, we see two close-by muons reconstructed for the same GEN displaced muon. One of the two reconstructed muons is displaced as we expected, the other is prompt (easier to see in the zoomin plot in [2]). But both has almost equal pT, eta and phi. More often, in many other events where GEN muon is displaced, the reconstructed muon is not displaced at all.
We also went back to the beginning of simulation chain for the specific event in [2], where we found there are duplicate close-by simulation hits in the muon detector for the same GEN displaced muon[3]( red dots indicate simulated hits in the CMS DT muon detector; purple dots indicate simulated hits in the CMS RPC muon detecor). This result in the downstream reconstructed close-by muons.
So it seems the generator level muon displacement information is not well simulated/
Cheers,
Wei
[1]
Boson (PDG id=3000022) mass 5GeV, average lifetime cTau=50mm:
https:/
[2]
https:/
Zoomin:
https:/
[3]
https:/
https:/
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