Geant4 Physics List

[marcodeltutto]

With PR #435 we switched to a new high-precision (HP) physics list. We should make the old and new ones both available so we can switch between the two as needed.

Plan is to keep SBN_QGSP_BERT_NNC to be the old one (so would need to be reverted) and create a new one with name SBN_QGSP_BERT_HP_NNC which contains the HP one.

This will require both SBND and ICARUS to point to the new list here:

• SBND: https://github.com/SBNSoftware/sbndcode/blob/252d833fd3849b82fcbbe7879870daecffe193a2/sbndcode/LArG4/larg4_services_sbnd.fcl#L11
• ICARUS: https://github.com/SBNSoftware/icaruscode/blob/ffa6d4167b9d44f86c1e79300e1c646c4eb730ce/fcl/g4/larg4_services_icarus.fcl#L11

[marcodeltutto]

Looking into this, I had the following question: why are we not using Geant4's official QGSP_BERT_HP instead of creating our own? I think it would be better to use an official Geant4 physics unless there is motivation for changing it. @linyan-w do you think it's okay if we use QGSP_BERT_HP?

I see that QGSP_BERT_HP differs from the current list in the following:

• has the additional G4RadioactiveDecayPhysics
• has the additional G4IonElasticPhysics
• used G4HadronElasticPhysicsVI instead of G4HadronElasticPhysicsHP

[linyan-w]

I was following the convention in SBN_QGSP_BERT_NNC. I have no objection to the official QGSP_BERT_HP physics list. @sjgardiner may have more thoughts there?

[marcodeltutto]

Then @Li-Jiaoyang97 I think we should revert SBN_QGSP_BERT_NNC to what it was originally, and then switch sbndcode and icaruscode to use QGSP_BERT_HP in the two places I mentioned above. Thanks!

[Li-Jiaoyang97]

Hi @marcodeltutto, sorry I think I completely missed this message last week. I will start to restore SBN_QGSP_BERT_NNC to what it was originally. Moerover, related to the usage QGSP_BERT_HP as default, do we need to do more test to confirm the CPU and wall time to confirm it is not too time-consuming? for both SBND and ICARUS case? Thank you!

[marcodeltutto]

Sounds good @Li-Jiaoyang97. Yes, I think including a CPU and time performances from a standard g4 job is useful! You can still make the PR to switch to QGSP_BERT_HP as this physics list is the preferred one and we should assume we are switching to this list. You can include the performances in the PR. If later on we think this is unbearable, we can consider switching back to SBN_QGSP_BERT_NNC.