FastSim track momentum resolution of high-pT muons

[sbein]

Charged gen particles with pT>1150 GeV have a suddenly poor track pT resolution in FastSim. This was identified in muons with W' MC events and confirmed with a muon gun (attached slides). This was originally discussed in the simulation meeting https://indico.cern.ch/event/1007716/contributions/4231234/attachments/2189371/3700030/FastSimBugsFeb2021b.pdf

The problem began with the jump from CMSSW_9_4_10 to CMSSW_9_4_11, when the package FastSimulation/SimplifiedGeometryPropagator/ was added. The relevant slides are posted here BadMuonSlides.pdf,

which show

• stand-alone muons are fine for pT>1150 GeV
• generalTracks matched to the high-pT muons have a completely blown up pT
• reco::muon or pat::muon "muons" get a pT that is ~2x higher than it should be.

[cmsbuild]

A new Issue was created by @sbein Sam Bein.

@Dr15Jones, @dpiparo, @silviodonato, @smuzaffar, @makortel, @qliphy can you please review it and eventually sign/assign? Thanks.

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[makortel]

Assign fastsim

[cmsbuild]

New categories assigned: fastsim

@mdhildreth,@sbein,@ssekmen,@lveldere,@civanch you have been requested to review this Pull request/Issue and eventually sign? Thanks