STAR Flow, Chirality and Vorticity PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 11/13/2020

Participants: Shaowei Lan, Shusu Shi, Xin Dong, Yue-Hang Leung, Yang Wu, Guannan Xie, Sooraj Radhakrishnan, Carl Gagliardi, Matt Posik, Daniel Brandenburg, Daniel Cebra, Hanseul Oh, Barbara Trzeciak, Hanna, Zbroszczyk, Xiaofeng Luo, ShinIchi Esumi, Jiangyong Jia, Prithwish Tribedy, Takafumi Niida, Rongrong Ma

Title: Disappearance of partonic collectivity in sqrt(sNN) = 3.0 GeV Au+Au collisions at RHIC

PWG: FCV

PAs: Shaowei Lan, Shusu Shi, Xin Dong, Yue-Hang Leung, Yang Wu, Guannan Xie, Sooraj Radhakrishnan, Nu Xu

Target journal: PRL

Proposal page: https://www.star.bnl.gov/protected/bulkcorr/slan/FXT3gev/paperProposal/shortPaper/

Presentation: https://drupal.star.bnl.gov/STAR/system/files/Shaowei_PWGC_11132020.pdf

The PWGC panel previewed the paper proposal from FCV PWG. The panel found that the paper should move forward. Several conveners recommended PRC rather than PRL and think that the paper should discuss more details shown in backup slides with longer paper. Previous results from AGS and GSI experiments should be acknowledged. The physics message needed to be sharpen considering those existing results. The following points were discussed during the preview.

Abstract:

Q. “4.5 GeV” is specifically mentioned in the abstract. How was it chosen? In Fig. 4, v2 from E877/E895/FOPI are compared and they covers 2<\sqrt{s_{NN}}<5 GeV. These results need to be acknowledged. This is also related to novelty and justification for PRL.

A. The number “4.5” is based on v1 results. PAs will consider to rephrase it.

C. This paper presents results not only for 3GeV but also for 27 and 54 GeV, which need to be mentioned in abstract. 

A. PAs will take it into account.

Figure 1 (slide 12):

Q. pT vs rapidity acceptance looks flat for pions, but not for proton and Lambda especially at positive rapidity. Was this effect taken care of when looking at pT-intagrated v1(y)? Similarly, the mean pT would be different for different particles, not only due to the physics but also due to the low pT cut-off from the acceptance. Have you considered/corrected the effect?

A. pT region was selected to be consistent with BES-I analysis but PAs understand the point and will think about it. 

C. Lambda may have additional effect from the efficiency.

Figure 2 (slide 13):

Q. UrQMD calculations are shown only for v2. Do you also do the comparison for v1?

A. Calculations can be found in backup slide 24 but they were not put in the paper.

C. Nice to have them, especially for K-, two versions of UrQMD show different sign and one of them looks close to the data.

Q. How did you tune the mean field parameters of UrQMD?

A. Not tuned. Just used the standard parameters.

C. In the UrQMD paper, different parameters predict different slope of v1. Would be interesting to look into that.

Figure 3 (slide 14):

Q. NCQ scaling is broken for positive particles, while it looks to work for negative particles at 3 GeV. Any comment/explanation?

A. Indeed K- scaled v2 is larger than K+ and close to protons. Likely it can be explained by associated production of K- with Lambda at this lower energy.

C. Nice to have such discussion in the paper.

Q. Dashed lines for 27 and 54 GeV look different from the data. Does this mean the fit doesn’t work so well at higher mT? Also the fit lines look different from what PAs show in the backup slide.

A. PAs will double-check on this. 

Figure 4 (slide 15):

Q. “\pi” and “K” are combined results of positive and negative particles? Previous results are also combined results?

A. Yes they are combined results. Note that at higher energies the charge difference is very small.

Q. PAs mentioned that EP was determined by TPC for 27 and 54 GeV and by EPD for 3 GeV. Have you tried to use EPD for 27 GeV.

A. Yes, but the resolution is ~1/3 compared to TPC.

Additional comments:

- Expecting that PAs reanalyze new picoDst for 3 GeV and make sure that the results don’t change.

- In previous STAR paper for 4.5 GeV, NCQ scaling looks to work. It would be nice if PAs can draw a sharp physics message from the comparison (3 vs 4.5 GeV).