sPHENIX discussion of physics

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

Hi Ming,

Thanks for sending that link - I agree, that’s a very interesting recent paper, which combines both HF capability + low-pT jets as you say. In p+p collisions, I should think sPHENIX can also explore this physics.

For me, the big question is what kind of control one can have for this in AA collisions. For these sub-structure observables, the background from the UE is often not “additive” (like it might be for a fragmentation function or a jet shape - where you can just statistically subtract it). This is because the UE particles may change the way the (de-)clustering proceeds. I know of some efforts to specifically develop techniques for this in AA, for example this work from last year: https://arxiv.org/abs/2006.01812 

I would be curious if there are jet experts from ALICE on this list who have some comment!

Dennis

On Sep 3, 2021, at 12:48 PM, Ming Liu <ming AT bnl.gov> wrote:

Dennis and all,

Very good idea, and I like your brief summaries.

 

Along the same theme -  here is a very interesting recent publication from ALICE (NATUTRE?),  https://arxiv.org/abs/2106.05713

Direct observation of the dead-cone effect in QCD

Love to further explore the physics in sPHENIX, with HF + Jet.

 

Cheers,

Ming

 

 

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Dr. Ming Xiong Liu P-3, MS H846 Physics Division   Office: 505.667.7125 Mobile: 505.412.7396 Los Alamos National Laboratory lanl.gov   <image002.png><image003.png><image004.png><image005.png>

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From: sPHENIX-physics-l <sphenix-physics-l-bounces AT lists.bnl.gov> on behalf of "Perepelitsa, Dennis" <dvp AT bnl.gov>
Date: Thursday, September 2, 2021 at 6:57 PM
To: "sphenix-physics-l AT lists.bnl.gov" <sphenix-physics-l AT lists.bnl.gov>
Subject: [Sphenix-physics-l] Physics Roundup - September 2021

 

Dear sPHENIX colleagues,

 

Since we are less than a mere 18 months from the start of first data-taking, I thought it would be fun to try to drive more “physics-focused” discussions within the Collaboration. To this end, I’d like to start a tradition, around the beginning of every month, of sending around a Physics Roundup of a few selected, recent papers along with brief considerations for sPHENIX.

 

Please feel free to reply to the thread with your thoughts - we could also set up a Mattermost channel if there is enough interest! 

 

I'll start with just two papers from earlier this year, from our friends at the LHC.

 

Dennis

 

— 

 

CMS, High precision measurements of Z boson production in PbPb collisions at sqrt(sNN) = 5.02 TeV, INSPIRE link, pub. PRL

 

Summary: CMS analyzes the 1/TAA-scaled yields of Z bosons as a function of centrality, and report a systematic dip in peripheral events, which they argue indicates the presence of geometric & selection effects. This would have implications for interpreting the measured charged particle RAA (for example) in very peripheral events.

 

Considerations for sPHENIX: The HI community is quite interested in validating the collision geometry & centrality selection using EW boson probes. Should we add “prompt photon RAA, out to as peripheral as we can go” to our list of high-priority, early analyses? That would be a nice way to crisply demonstrate that sPHENIX has control over centrality selection & modeling. (And it will be easier to calibrate photons than jets early in the program!)

 

— 

 

ALICE, Measurement of the groomed jet radius and momentum splitting fraction in pp and Pb–Pb collisions at sqrt(sNN) = 5.02 TeV, INSPIRE link  sub. PRL

 

Summary: ALICE analyzes ~60 GeV track-jets, R=0.2 in central events, R=0.4 in semi-central ones, with a particular choice of SoftDrop parameters. They report that z_g is not modified in Pb+Pb collisions, but that theta_g peaks at lower values, and thus claim this demonstrates that the QGP medium modifies the angular structure of the parton shower.

 

Considerations for sPHENIX: We should strive to be doing this kind of physics, but with sufficient systematic control to push to significantly lower jet pT and/or larger R. I personally think it would be quite interesting to go so low that typical sub-jet pT scales begin to be similar to QGP medium scales. For the sPHENIX scientific case, we have argued that jet evolution at RHIC is significantly more medium-dominated than at the LHC - should we thus expect to see strong modifications in the parton shower structure?

 

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Dennis V. Perepelitsa

Assistant Professor, Physics Department

University of Colorado Boulder