S2 bottom pattern hit map not used in fax

[mcfatelin]

After a more close look at code:

• I found that currently the S2 bottom pattern hit map is not used in simulating the S2 hits. See L637 of pax.simulation. The bottom S2 pattern is assumed to be uniform.
• In the mean time, fax uses a constant value of s2-top-fraction to allocate photons for a simulated S2 on top/bottom PMTs (See L245 of XENON1T.ini ). And the value is not updated to the latest value got from new MC simulation (See here ). This is the reason we see discrepancy of AFT between data and MC in Joey's note Fig.3

Suggest to:

• Update the s2_mean_area_fraction_top of L245 of XENON1T.ini to the latest value from MC simulation
• Or in long term to include also bottom PMTs in S2 hit pattern map so that we get rid of the separate treat of S2 hit on top/bottom PMTs. L637 of pax.simulation

[JelleAalbers]

Yes, this is correct. I agree changing the value in the ini would be the easy solution for now, including the bottom PMT hit map would be the best solution long-term.

[JelleAalbers]

I'll change the title since I understand you've resolved the second part of the issue. Once a top+bottom S2 map is made, we'll still have to change fax to support it (and still support top-only maps ideally).

[l-althueser]

Fyi: The latest S2 map is extracted from MC for top+bottom PMTs. Changes in PAX/FAX are still missing.