Include Muon-Conversion in Midshower Enriched Background Sample

[tomeichlersmith]

While the ECal as Target analysis was able to investigate up to 1E13 EoT equivalent using the "enriched nuclear" background (i.e. background events where photo-nuclear and electro-nuclear interactions lead to mis-measured energy in the ECal), the photon conversion to muons background is expected to grow in importance as we scale up to higher EoT. For this reason, it should be included in the midshower backgrounds alongside EN and PN.

[tomeichlersmith]

I am not planning on including "Muon-Conversion" (a.k.a. Dimuon) events in the Midshower Enriched Nuclear sample generation. I think it is too confusing for two reasons.

1. The absolute rates of these types of interactions are different by a few orders of magnitude so we would need to manually skim out the dimuon subsample anyways to make it easier to analyze.
2. I've already generated a large enriched nuclear sample for 4GeV and I am 3/4 of the way through generating one for 8GeV and I don't want to have to re-generate these large and CPU-intensive samples.

Therefore, I am starting a new filter that will be very similar to the MidshowerNuclearBkgdFilter but focused on DiMuon rather than Nuclear process(es). I've linked the branch I'm working on and it looks good so far, just need to generate a full file and see how the distributions look.

[tomeichlersmith]

In the current implementation of Dimuon production, there are four different simulation parameters.

• Sorting Threshold The energy threshold that defines "high" and "low" energy particles for the sorting. All "high" energy particles are processed first.
• Biasing Threshold The energy threshold above which photons need to be to be biased.
• Biasing Factor The factor that is multiplied into the cross section to artificially increase the rate of dimuon production.
• Filter Threshold The minimum total energy given to muons in order for the event to be kept.

In order to simplify the parameter space, I've set the Sorting Threshold equal to the Biasing Threshold basically meaning all biased, high-energy photons will be processed, then we check if the event should be kept, and then we only process the rest of the shower if we are keeping the event.

Initially, I am keeping the Biasing Factor set to its target-dimuon value of $10^4$. This produces some events where multiple muon-conversions occur, but these are also down-weighted and so can be neglected for now. This leaves the Biasing (and Sorting) Threshold $E_B$ and the Filter Threshold $E_\mu$ to be studied.

First, we can generate a few different samples to check that the filtering threshold is operating as expected. We see that it is -- the distributions are cut that the filtering threshold and are otherwise not distorted relative to each other.