sPHENIX discussion of physics

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

Hi sPHENIX colleagues,

With so many interesting measurements presented at the Quark Matter conference, it is difficult to choose just one or two per month. But for this month, I’d like to take a look at the recent observation by CMS of the Upsilon(3S) in Pb+Pb collisions.

You may know that some experiments at CERN have been pausing paper submissions to the arXiv, so the best reference at the moment is the following Preliminary writeup:

CMS, Observation of the Y(3S) meson and sequential suppression of Y states in PbPb collisions at sqrt(sNN) = 5.02 TeV, https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/HIN-21-007/index.html 

CMS measures the RAA for the Y(3S) to be on the order of half of what it is for the Y(2S). Interestingly, the theoretical predictions were all over the map with, e.g., one calculation greatly over-predicting the Y(3S) suppression despite matching the Y(1S) and Y(2S) results in detail. So the data are really informing theory.

For us in sPHENIX, a natural question is - given the assumption that the relationship between the 2S and 3S is similar at RHIC as at the LHC - what would be our prospects for making a statistically significant measurement? We discussed this in the HF TG group, and we will try to include such a projection in the Beam Use Proposal. For reference, the latest STAR measurement on Upsilon suppression at RHIC is a Preliminary result first shown in 2018 [1].

As another interesting technical note, the measurement was performed using a BDT on the candidate di-muon vertex properties to increase the significance of the signal, and with some significant fixing of line shape parameters.

Dennis 

[1] https://drupal.star.bnl.gov/STAR/files/Upsilon_draft_QM2018v13_0.pdf