sPHENIX discussion of physics

["Sickles, Anne M" <sickles AT illinois.edu>]

Hi all,

Thanks Dennis for starting this and Ming for chiming in.  I had a few thoughts…

 

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!)

 

I agree this is both important and very impactful.  I went hunting for existing measurements at RHIC and found this PHENIX paper:

https://inspirehep.net/literature/1116179 but nothing more recent (please let me know if I missed something).  

Even with the 2023 AuAu data alone we should have a big improvement in statistics (and acceptance) than the PHENIX measurement.  Do we have a projection plot of the photon RAA as a function of centrality?  That would be great to see.  Since we’re interested in the modeling, perhaps just Ncoll scaled yields would be interesting as well (since we won’t have pp data until 2024).

With regard to the jet measurements brought up by Dennis and Ming, I think in general we should be pushing the theory community provide predictions for sPHENIX jets so that we can understand where we might have a particularly different sensitivity than at the LHC.  This can help us target our resources most effectively.

Best,

Anne

---------------------------------------------------------

Anne Sickles

Associate Professor

University of Illinois at Urbana Champaign

sickles AT illinois.edu

---------------------------------------------------------

On Sep 7, 2021, at 11:32 AM, Perepelitsa, Dennis <dvp AT bnl.gov> wrote:

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>

-- 

 

 

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?

 

_______________________________________________ sPHENIX-physics-l mailing list sPHENIX-physics-l AT lists.bnl.govhttps://lists.bnl.gov/mailman/listinfo/sphenix-physics-l

Dennis V. Perepelitsa

Assistant Professor, Physics Department

University of Colorado Boulder

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