STAR Correlations and Fluctuations PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 6/18/2021

Participants: Ashish Pandav, ShinIchi Esumi, Xiaofeng Luo, Bedanga Mohanty, 
Toshihiro Nonaka, Nu Xu, Yu Zhang, Barbara Trzeciak, Daniel Cebra, Hanna 
Zbroszczyk, Jiangyong Jia, Maria Zurek, Matt Posik, Md. Nasim, Prithwish 
Tribedy, Raghav Elayavalli, Hanseul Oh, Sooraj Radhakrishnan, Yi Yang, 
Rongrong Ma, Takafumi Niida

Title: Beam energy dependence of fifth and sixth order net-proton number 
fluctuations in Au+Au collisions at RHIC
PAs: Ashish Pandav, ShinIchi Esumi, Xiaofeng Luo, Bedanga Mohanty, Toshihiro 
Nonaka, Nu Xu, Yu Zhang
Target journal: PRL
Proposal page: 
https://drupal.star.bnl.gov/STAR/system/files/Netp_BES_C56_paper_drupl_e2.html
Presentation: 
https://drupal.star.bnl.gov/STAR/system/files/PWGC_preview_e2_pa.pdf

The PWGC panel previewed the paper proposal from CF PWG. The panel found that 
the results are interesting and all agree that the paper should move forward 
but the physics message should be sharpened to meet PRL criteria and for 
general readers. The following discussion was made during the preview.

slide 6:
Q. Why 2011 data for 27 GeV instead of 2018 data?
A. Some difference was found compared to published results. Also, all other 
datasets are from BES-1, to be consistent, BES-1 data was used.

slide 8:
Q. There is mismatch between embedding data and real data at 3 GeV. Such a 
difference was considered into the systematic uncertainty?
A. PAs were not aware of it but will look into it.

Fig. 2:
Q. Figs. 2 and 4 present almost same data in different way. Any specific 
reason?
A. To better show the hierarchy trend of cumulant ratio, i.e. C3/C1 > C4/C2 > 
C5/C1 > C6/C2, as expected from LQCD models.

Q. Does FXT have different acceptance from collider data? Any acceptance 
study?
A. Not in this paper, but in 200 GeV C6 paper and recent net-p paper (only 
for n<=4). In general, reduced acceptance makes the ratios closer to the 
statistical baseline.
Q. Looking at Fig. 4, big change between 3 GeV and 7.7 GeV is seen. If you 
require similar asymmetric acceptance at 7.7 GeV like FXT 3 GeV (|y|<0.5 -> 
-0.5<y<0), how does this gap change?
A. y-acceptance was varied symmetrically but not asymmetrically, PAs will 
check on this.

Q. What is the significance of the deviation from the baseline (zero in this 
case)?
A. ~2sigma or lower.

Fig. 3:
Q. Why the two-component model is not available for \kappa_4 and peripheral 
events?
A. Two-component model uses the data from 1st to 4th-order cumulants as 
inputs and then predicts 5th and 6th orders. Calculations for peripheral data 
can be done.
C. It may be useful to do null test with UrQMD, use UrQMD C1-C4 as inputs 
then see if C5,C6 predicts same as calculated in Fig. 3. 
C. Conclusions in the summary and this plot are confusing. Probably matter of 
how to present. Legend here may be also misleading.

Fig. 4:
Q. UrQMD shows similar change to the data below 10 GeV. Why so? How many 
UrQMD points are there?
A. Only one point for 3 GeV below 7.7 GeV but also PAs have checked 4.5 GeV, 
where similar trend was seen. In general, larger muB leads to larger cumulant 
ratio.

Summary slide:
Q. How can we understand the increasing negative trend in decreasing energy?
A. QCD-based FRG model also shows similar trend (see slide 4).

C. Please make sure if there is no contradiction in data with 
ongoing/submitted papers, 3 GeV paper and 200 GeV C6 paper.

Q. What’s the main message of this paper? What is new gain compared to C4 
paper?
A. 3 GeV shows different behavior indicating a hadronic matter created, while 
QCD matter at 200 GeV. At low energy (<11.5 GeV), a hint of two-compnent, 
possibly indicating a QCD phase transition and critical point. We are also 
testing QCD thermodynamics. The hierarchy of cumulant ratios expected by LQCD 
is now seen in the data, which is new.

Q. Fig. 2 seems a main plot of this paper. Any way to violate the behavior, 
e.g. UrQMD? Any other model at 3 GeV.
A. UrQMD doesn’t show such an ordering. No model except UrQMD is available 
for 3 GeV at this moment.