Increase the number of processes in the process map

[EinarElen]

By default, we are only including entries that are interesting for electrons and photons. This leads to most entries in the particle tables to be marked as "unkown" which has caused confusion for some users. When working on #106, I needed to be able to check that the daughters of a primary kaon were from its decay or not so I needed an entry for at least the Geant4 "Decay" process.

Adding more entries to the process map will increase the runtime for SimParticle::findProcessType which will have to search a larger map. I would argue that if we are running into performance issues because of this, we should look at the datastructure and algorithm we are using (map + string comparison) first.

We should think through what particle + process combinations we are especially interested in, off the top of my head

• Kaons
• Neutrons

[tomeichlersmith]

I forget where my previous comments went (maybe they were just on slack), but I would like to add a Primary category so that primaries have a different process type than unknowns. The offending lines of code are

SimCore/src/SimCore/TrackMap.cxx

Lines 68 to 74 in f1988b5

	const G4VProcess* process{track->GetCreatorProcess()};
	if (process) {
	const G4String& name{process->GetProcessName()};
	particle.setProcessType(ldmx::SimParticle::findProcessType(name));
	} else {
	particle.setProcessType(ldmx::SimParticle::ProcessType::unknown);
	}

This means a particle has the "unknown" type if it is either a primary (no creator process) or the creator process does not exist in the mapping. Maybe this motivates a more direct naming scheme for unknown? Split it into NoCreator (which is just primaries unless something really customized is happening) or Unknown (which is the creator exists but it isn't in the map).

[EinarElen]

I think no creator would lead people unfamiliar with Geant4/ldmx-sw internals to get confused. If we add a primary type and some more that we think are relevant for other analyses & particles, that should make unknown more reliable. Maybe we could call it something more like unspecified?

[tomeichlersmith]

Good point, keeping it Primary helps a larger number of users, folks worrying about NoCreator distinction would already be deep in the weeds.

The other names for the unknown category I can think of are NotListed or if we want to get really fun NotListedInSimParticleProcessMap to really convey to any user that it is just a choice we make.

[EinarElen]

I think having primary be a distinct category also lets people write simple validation things like "what's the X or the primary/primaries daughter" a lot easier for new folks so getting this in would be valuable

[EinarElen]

One type of process that I think would be valuable to track is inelastic hadronic interactions. This could be one "hadronInelastic" or a couple like "neutronInelastic" "kaonInelastic", "otherInelastic" etc.

[tomeichlersmith]

As far as running into performance issues, I don't think that's a concern. findProcessType is only called on the saved tracks after they are full simulated. This means it is only called a few dozen times during an event meaning performance will still be dominated by other affects in the simulation.

That being said, I don't have any quantitative measurements to back this up.