15_0_X Added Pythia-based Rhadron decays during Geant simulation

[ctdax]

PR description:

PR validation:

If this PR is a backport please specify the original PR and why you need to backport that PR. If this PR will be backported please specify to which release cycle the backport is meant for:

Backport of #49414 to CMSSW_15_0_X for intermediate release cycle.

[cmsbuild]

A new Pull Request was created by @ctdax for CMSSW_15_0_X.

It involves the following packages:

• PhysicsTools/HepMCCandAlgos (analysis)
• SimG4Core/CustomPhysics (simulation)

@civanch, @cmsbuild, @kpedro88, @mdhildreth, @tvami can you please review it and eventually sign? Thanks.
@bsunanda, @fabiocos, @makortel, @martinamalberti, @rovere, @slomeo this is something you requested to watch as well.
@ftenchini, @mandrenguyen, @sextonkennedy you are the release manager for this.

cms-bot commands are listed here

[cmsbuild]

cms-bot internal usage

[tvami]

@cmsbuild please test

[cmsbuild]

+1

Size: This PR adds an extra 24KB to repository
Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-b0de44/52418/summary.html
COMMIT: 13a9c60
CMSSW: CMSSW_15_0_X_2026-04-01-2300/el8_amd64_gcc12
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week1/cms-sw/cmssw/50629/52418/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• You potentially removed 4 lines from the logs
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 50
• DQMHistoTests: Total histograms compared: 4032954
• DQMHistoTests: Total failures: 23
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 4032911
• DQMHistoTests: Total skipped: 20
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 49 files compared)
• Checked 218 log files, 189 edm output root files, 50 DQM output files
• TriggerResults: no differences found

[tvami]

+1