Fix to allow G4 simulation of the long-lived susy-tau (1000015) decay products

[shedprog]

PR description:

The issue is described under the following link: #36706
And related to the following dicussion: https://hypernews.cern.ch/HyperNews/CMS/get/simDevelopment/1997/1/1/1.html

In the corresponding PR we add fix in order to prevent the duplication of the decay products of the long-lived charged stau (1000015), the gen particles are generated by the Pythia:

In order to add the whole decay chain of stau using the following function without chain break

cmssw/SimG4Core/Generators/src/Generator.cc

Line 396 in df76a09

particleAssignDaughters(g4prim, (HepMC::GenParticle *)*pitr, decay_length);

we need to prevent iterations from stopping at the particle with intermediate status=23 which highlighted on the picture above.

The check of the mother pdgId == 1000015 is added to apply the fix only specifically for stau MC.

PR validation:

• the basic style tests specified on the following page are performed http://cms-sw.github.io/PRWorkflow.html

• runTheMatrix tests results:
  runTheMatrix.log

• the visual inspection shows that after corresponding fix, SimTracks are not duplicated
  before the fix
  
  after the fix
  

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-36772/27907

• This PR adds an extra 16KB to repository

[cmsbuild]

A new Pull Request was created by @shedprog (Mykyta Shchedrolosiev) for master.

It involves the following packages:

• SimG4Core/Generators (simulation)

@cmsbuild, @civanch, @mdhildreth can you please review it and eventually sign? Thanks.
@makortel, @cvuosalo, @rovere, @bsunanda, @fabiocos, @slomeo this is something you requested to watch as well.
@perrotta, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

[civanch]

please test

[civanch]

@shedprog, let us remove "draft" from this PR. This minimal fix do not affect any other analysis, because is active for exclusive vertex. It is safe.

Do you check independently two cases: stau decay inside beam pipe and outside beam pipe?

[cmsbuild]

-1

Failed Tests: RelVals-INPUT
Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-cf940b/21915/summary.html
COMMIT: 5f4cdfc
CMSSW: CMSSW_12_3_X_2022-01-21-2300/slc7_amd64_gcc10
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/36772/21915/install.sh to create a dev area with all the needed externals and cmssw changes.

RelVals-INPUT

• 4.764.76_ZMuSkim2012D+ZMuSkim2012D+HLTDSKIM2+RECODR1reHLT2+HARVESTDR1reHLT/step2_ZMuSkim2012D+ZMuSkim2012D+HLTDSKIM2+RECODR1reHLT2+HARVESTDR1reHLT.log

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 43
• DQMHistoTests: Total histograms compared: 3465668
• DQMHistoTests: Total failures: 0
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3465646
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 42 files compared)
• Checked 181 log files, 42 edm output root files, 43 DQM output files
• TriggerResults: no differences found

[civanch]

This PR is fine, failed WF does not mean that there is a problem.

[shedprog]

@shedprog, let us remove "draft" from this PR. This minimal fix do not affect any other analysis, because is active for exclusive vertex. It is safe.

Do you check independently two cases: stau decay inside beam pipe and outside beam pipe?

Yes, in our MC we have all the cases,

1) for the cases of decay inside the beam pipe (<theDecRCut2) no SimVertexes are created for the stau and tau (matched SimVertexes/SimTracks are in red)

2) for the cases with long-lived stau it looks the following

[civanch]

+1

@shedprog , please, make backport of this PR to CMSSW_10_6_X - legacy Run-2 branch.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next master IBs (but tests are reportedly failing). This pull request will now be reviewed by the release team before it's merged. @perrotta, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[perrotta]

+1

[perrotta]

merge