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Fixed muon stopping #33

Closed civanch closed 6 years ago

civanch commented 6 years ago

In production with CMSSW_9_4_0_patch1 https://hypernews.cern.ch/HyperNews/CMS/get/prep-ops/5409.html a problem in Geant4 was reported. After investigation it turn out that there is rare problem in simulation of mu- absorption at rest by the Bertini cascade, when kinematics of final state may be broken. The fix preserves the same method of sampling, so simulation history will not be changed until such rare event, for which the problem was observed. After such event the simulation history will diverse. So, in standard jenkins tests results should agree with the baseline due to limited statistic. No change of any physics observable is expected. The fix should be back ported to Geant4 10.2, whihc is used in CMSW_9_3_X and 9_4_X.

cmsbuild commented 6 years ago

A new Pull Request was created by @civanch (Vladimir Ivantchenko) for branch cms/4.10.04.

@cmsbuild, @smuzaffar, @gudrutis, @mrodozov can you please review it and eventually sign? Thanks. You can sign-off by replying to this message having '+1' in the first line of your reply. You can reject by replying to this message having '-1' in the first line of your reply.

external issue cms-sw/cmsdist#4140

fabiocos commented 6 years ago

@civanch I assume that this fix is going to be applied also to the official Geant4 distribution, am I correct?

civanch commented 6 years ago

@fabiocos , definitely yes for the development version but not sure about official patches, moreover, we in CMS will likely do not take any new Geant4 patch for Geant4 10.2. Also am not sure if we will consider Geant4 official patches for 10.4. So, Geant4 internally will validate the fix independently of us.