Explore efficacy of recoil electron selection

[oscarplewis]

Issue description

At present, the relevant function ecal::trackProp picks out the recoil electron track to propagate forward into the ECal by simply returning the first valid track state. But this has the potential to erroneously select a track that is not the interacting recoil electron (for instance, the abundance of low pT recoil electrons here), especially in the case of multi-electron events. Moreover, how effective is this existing strategy to accurately find the recoil electron, and how does it compare to the simulation scoring plane selection (which should be the "truth")?

Tasks

• Evaluate efficacy of existing selection function
• Compare to selecting the maximal pT track as the recoil track
• How does discriminating against positive QoP values turn out? Is it worth selecting only negative QoP tracks for picking the electron? (this will require checking the error rate in the tracking algorithm at which the electron tracks are mischaracterized and assigned positive QoP)
• ... and other questions that have yet to be thought of ...

Existing material to start off

• ecal::trackProp function at HEAD
• Possible pT-max-finding function with QoP discrimination

[oscarplewis]

I've run some preliminary studies on certain track finding functions here, but I haven't gone much into depth about which function is best or how they can be optimized, nor have I touched 2e stuff, so there's still good work to do here. trackProp is the existing function that gets the first valid track state with values in the Ecal; pTTrackProp selects the track with the greatest transverse momentum; pTrackProp picks the track with greatest total momentum; chi2TrackProp picks the one with the minimum track fitting chi^2 / ndf.

WABs:

Signal 1 GeV:

Signal 100 MeV:

Signal 10 MeV:

Signal 1 MeV:

Ecal PN: