Change PE and amplitude definition for RecHits

[cmantill]

This PR changes the definition for a RecHit's number of PEs and amplitude - for a double-ended readout bar. It solves #16.
I also included a note on the expected translation of recHit energy <=> incident particle energy with a rough estimate of the sampling fraction - as derived from @therwig . We should follow up with a calibration.

[therwig]

Looks good to me! (And I guess for now we can actually apply the calibration in the analysis step, still good to document.)

[tomeichlersmith]

I just have one big question that is scatter across my comments.

Why don't you divide by the approximate sampling fraction in the rec producer? Or, if you don't want to include it now, why do you multiply by the sampling fraction in the test (to undo a division by it)?

Otherwise, this looks good.

[cmantill]

@tomeichlersmith, @mrsolt I have decided to:

• Keep the sampling fraction out of the reconstructed energy (since we will likely have to include other calibrations, and these should go after the improvement on the digis - simulation of photon arrival time - that we are working on)

• This PR still changes the voltage estimate, from:

  • an average voltage of both ends of the bar, where at each end the attenuation is reversed with an approximate estimate of the position, to:
  • the sum of voltages of both ends of the bar

• This modifies both the number of PEs and the hit energy

• To help calibration/debugging in later stages, I have included in Amplitude, the average of the energy estimated at each of the bar after reversing the attenuation (with that approximate estimate of the position).

For reference, here is how the number of "reconstructed" PEs varies in different averaging/attenuation scenarios in double-readout, for one single SimHit with 4.66 MeV (~MIP), ~68 "simulated" PEs:

• when not considering attenuation and summing voltage: 91 PEs (this PR)
• when considering attenuation and averaging voltage: 62 PEs (old)
• when not considering attenuation and averaging voltage: 45 PEs
• when considering attenuation and summing voltage: 124 PEs