sPHENIX discussion of software

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

Hi all,

As promised in the Jet Structure meeting on Monday, please find some slides 
with a mid-week update.

Key points: 

1. The strange JER in pp collisions arises from an aspect of the HI-style jet 
reconstruction. The minimum seed jet pT, which essentially sets how 
permissive is the identification of jet-like regions to exclude from the 
background determination, was chosen to be quite large. This can result in a 
“self-energy” bias for low-pT jets, in which their energies are included in 
the background determination, causing a systematically low response. This 
resulted in a double-peak structure in the response distributions, first 
noticed by Jeff, arising from jets which do / do not have a seed jet nearby. 

While in Au+Au events, it makes sense to have a somewhat high minimum seed 
jet pT (so that one does not accidentally exclude background fluctuations — 
although just where to set it is still an open question), this is clearly too 
high for p+p collisions. I will rerun some p+p MC with a lower seed jet pT 
threshold, although that will mean that we SHOULD expect some difference in 
the mean pT response between pp and Au+Au at low-jet-pT.

I’d be particularly happy for input on this point.

2. I have updated the dijet xJ plot with full statistics, and I have made two 
versions: one with small cone size and high-pT where there is no appreciable 
centrality-dependence in the reco-level distribution, and one with large cone 
size / small-pT where there is. This followed from a nice suggestion by Aaron 
(who also had other suggestions I have not yet gotten to).

3. The photon+jet simulations have finished and Kurt Hill, a student at 
Colorado, has made some xJg distributions in the same spirit as the dijet xJ 
distributions, again showing a case where one can / cannot observe a 
centrality-dependence in the reco-level distribution.

Happy for any feedback — will keep working towards the presentation of these 
at the General Meeting,

Dennis 

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

Attachment: dvp-sPHENIX-update-4-18-18.pdf
Description: dvp-sPHENIX-update-4-18-18.pdf