sPHENIX HCal discussion

["Perepelitsa, Dennis" <dvp AT bnl.gov>]

Dear Inner HCal team (CC: Jet Structure TG),

At the Collaboration Meeting, I promised you a fast look at the SoftDrop performance with and without reading out the IHCal to see if this could be a good contribution to the physics-driven motivation for the IHCal. I attach some slides characterizing the pT, zg (subjet energy fraction), and Rg (subjet angular separation) “response” for 30-40 GeV truth jets at mid-rapidity, using an Al IHCal with and without instrumentation. 

(Incidentally, this is our first look at these quantities within sPHENIX — if people are interested I can initiate a PR for configuring SoftDrop to run as part of our jet finding within sPHENIX and adding these quantities as “properties” of jet objects).

We have some ability to reconstruct Rg (angular separation between subjets), but the detector effects are non-trivial.

Unfortunately, with a purely calorimetric reconstruction, our ability to reconstruct zg is very small. I suspect this is because, if one is looking at ~30 GeV jets and the z_g distribution is peaked at ~0.1, one is asking the calorimeter to measure the energy of 3 GeV (!) subjects. A layer-by-layer calibration could help modestly (my study is pure EM-scale), but one probably really wants assistance from tracking information. 

In both cases, the differences between using and not using the IHCal are quite small. So this is not going to be a good argument for the NSF MRI. 

Happy for any comments, or to help people get set up with their own more detailed study. Sorry this was not a slam dunk, 

Dennis

Dennis V. Perepelitsa
Assistant Professor, Physics Department
University of Colorado Boulder

Attachment: dvp-sPHENIX-IHCalSoftDropStudy-12-12-18.pdf
Description: dvp-sPHENIX-IHCalSoftDropStudy-12-12-18.pdf