sPHENIX discussion of physics

[Kolja Kauder <kkauder AT gmail.com>]

Hi Jörn, Dennis,

Just a side note: I _think_ pythia6's shower ordering changed from Q to pT during the life of pythia6, although it has of course evolved further since in Pythia8 and now DIRE and VINCIA are options. Peter Skands has a (somewhat cryptic) overview here starting in the Backups, officially slide 37, in practice 57

http://skands.physics.monash.edu/slides/files/12-apr-atlas.pdf

Best,

Kolja

On Wed, Jun 22, 2022 at 2:11 PM Joern Putschke <joern.putschke AT wayne.edu> wrote:

Hi Dennis,

 

If you one looks into more detail of PYTHIA8 Rg, zg vs RHIC data, please have a look at this paper: https://inspirehep.net/literature/1783875

One notices that for larger R jets and/or higher pT Pythia8 becomes better in describing Rg (and also Mg,M see other paper).

Why PYTHIA6 is in general better, in particular at lower pT than PYTHIA8 I am not sure, the default shower ordering changed from 6 to 8 (at least as far as I know) for example. It might worthwhile to consider inviting the Pythia8 people for a discussion to get a better understanding and maybe spark their interest for 200 GeV data with sPhenix data around the corner …

 

Thanks

 

Joern

 

From: Perepelitsa, Dennis <dvp AT bnl.gov>
Date: Wednesday, June 22, 2022 at 10:25 AM
To: Joern Putschke <joern.putschke AT wayne.edu>, Liu, Ming <ming AT bnl.gov>
Cc: sphenix-physics-l AT lists.bnl.gov <sphenix-physics-l AT lists.bnl.gov>
Subject: Re: Physics Roundup - June 2022

Hi Ming and Joern,

 

Thanks - this is exactly the kind of discussion I was hoping to spark.

 

Ming, I would be curious if there is a publicly-shareable plot you can show of how the different tunes compare to J/psi vs. multiplicity data. That sounds like exactly like the kind of measurement where this would have a big impact.

 

Joern, I appreciate your point that the impact is much larger for the mass observables. (I guess the right-hand side of Fig 3 and the bottom of Fig 15 are groomed and ungroomed, respectively.) On a related note, do you know why Pythia8 (no matter the tune) seems to do an OK job describing z_g but less so R_g? 

 

Dennis

On Jun 22, 2022, at 7:37 AM, Joern Putschke <joern.putschke AT wayne.edu> wrote:

 

Dear Dennis/All,

 

Thanks for starting the discussion on PYTHIA tunes. That RHIC energies requires different parameters and that somehow the extrapolation to lower energies (the assumed energy dep of, in particular, the MPI/CR parameters)( does not seem to work very well, was also observed back in the days with Pythia6, which was also tuned, but a bit more adhoc than the current PYTHIA8 tune. So, with that in mind it is not too surprising that the same held up for PYTHIA8.

Concerning the groomed observables, maybe I am missing something, but zg and Rg (Fig 15) seem pretty insensitive to the soft tuning, however the groomed mass and mass in general is more sensitive o the soft physics. For the mass that is certainly not too surprising, for the groomed mass, since you still take all particles of the groomed jet as supposed to quantities derived from the two prongs, I would have expected some influence of the soft physics with the 0.1 cut, which given the kinematics of RHIC jets (a couple of GeV) could be affected to some degree by the soft UE more than at the LHC.

What I found interesting is that PYTHIA8 seems to have more trouble describing the jet mass, Mg and Rg , than the old PYTHIA6 tune (see comparisons, not to the Detroit tune in https://inspirehep.net/literature/1853218 ). If this is only due to changes in the soft part or if the different parton shower ordering matters too would be interesting to follow up.

 

Thanks

 

Joern

 

 

From: sPHENIX-physics-l <sphenix-physics-l-bounces AT lists.bnl.gov> on behalf of Perepelitsa, Dennis <dvp AT bnl.gov>
Date: Monday, June 20, 2022 at 5:31 PM
To: sphenix-physics-l AT lists.bnl.gov <sphenix-physics-l AT lists.bnl.gov>
Subject: [Sphenix-physics-l] Physics Roundup - June 2022

[EXTERNAL]

Dear sPHENIX colleagues, 

 

This month, I’ve been reading a paper which does not contain a physics measurement, but is rather focused on modeling for jet physics:

 

Aguilar et al, PYTHIA8 underlying event tune for RHIC energies, INSPIRE link, pub. PRD

 

This paper tunes parameters in Pythia related to how the generator deals with multi-patron interactions (MPIs) and color reconnection (CR) to a variety of STAR and PHENIX data. The data include charged pion and Drell-Yan cross-sections, properties of the underlying event properties, and groomed jet observables.

 

The RHIC data appear to favor rather different values for these MPI/CR parameters than those used by some existing popular tunes which are largely driven by LHC data. In the end, the authors produce a new “Detroit” tune for RHIC energies.

 

For me personally, I was surprised to see that Pythia parameters related to “soft physics” (UE production, hadronization) have as big an effect as they do on groomed jet observables - which are designed to be less sensitive to the details of the soft processes.

 

As we move closer to producing simulations to support real physics analyses in data, we may want to look more closely at their tuning. Any thoughts?

 

Dennis

 

Dennis V. Perepelitsa

Assistant Professor, Physics Department

University of Colorado Boulder

 

 

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Kolja Kauder, Ph.D.
NPPS, EIC
Brookhaven National Lab, Upton, NY
+1 (631) 344-5935

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