Strange behavior of muon pairs photoproduction cross section in Geant4 11.2 version


I am trying to produce muon pairs from photons (photon energies of 4.4 GeV) using latest version of GEANT4 11.2 on lxplus. I use the standard “FTFP_BERT” physics list. I used the following commands for activating the muon photoproduction process

/physics_lists/em/GammaToMuons true
/physics_lists/em/GammaToMuonsFactor 1000 (or 1 or 100)

1. Changing the factor did not give any change in muon pair yield. It seems the factor is not doing anything?
2. For low 300 MeV photons I get much more muon pairs without biasing (using Factor =1).

I have done similar simulations few years ago with GEANT4 10.6 and the behavior with this version was as expected. With the 10.6 version I had to use Factor=1000 to see muon pairs ( photons energy=300 MeV, target 1cm graphite).

Could you please let me know if something in the behavior has changed?


Thank you Armen for this report. In new patches the fix will be introduced.


Hi Vladimir,
Thank you very much.