STAR Correlations and Fluctuations PWG

[Takafumi Niida <niida AT bnl.gov>]

Date: 6/25/2021

Participants: Jin Wu, Yufu Lin, Zhiming Li, Xiaofeng Luo, Barbara Trzeciak, 
Daniel Brandenburg, Daniel Cebra, ShinIchi Esumi, Hanna Zbroszczyk, Jiangyong 
Jia, Maria Zurek, Prithwish Tribedy, Qinghua Xu, Raghav Elayavalli, Hanseul 
Oh, Sooraj Radhakrishnan, Rongrong Ma, Takafumi Niida

Title: Energy Dependence of Intermittency for Charged Particles in Au+Au 
collisions at RHIC
PAs: Jin Wu, Yufu Lin, Zhiming Li, Xiaofeng Luo, Yuanfang Wu
Target journal: PRL
Proposal page: 
https://drupal.star.bnl.gov/STAR/blog/wujin/energy-dependence-intermittency-charged-particle-au-au-collisions-rhic
Presentation: 
https://drupal.star.bnl.gov/STAR/system/files/Intermittency_paper_proposal-pwgc-Jun25.pdf

The PWGC panel previewed a paper proposal from CF PWG. The panel found that 
the results are interesting and the paper should move forward. Many conveners 
think that the physics message with the current form is not clear and strong 
enough for PRL. Other journals such as PLB and PRC with more explanation in a 
longer paper are mentioned as possible choice. Theoretical guidance would be 
helpful to clarify the point. The following discussion was made.

Slide 5
Q. This was studied in px-py space. Any attempt to do in different space, 
e.g. pt,phi,eta. If you do so, do you expect any difference?
A. Motivated by references in slide 5, which suggest analysis in transverse 
momentum space, also following previous studies in NA49,61. PAs do not know 
if we expect difference when using different space.

Slide 10
Q. PID is mentioned here but how did PAs use PID information? Results seem to 
be for charged particles.
A. Analyzed pions+kaons+protons as charged particles.

Slide 11
Q. How the average efficiency was calculated?
A. Efficiency depending on pT of particles in cell are averaged to get 
average efficiency of the cell. 

Q. Did PAs use the same way for correcting efficiency as higher moment 
analysis? Also other experimental effects, e.g. bin width correction, 
auto-correation, overcorrection in high multiplicity event because of fewer 
events, are also taken care?
A. They are taken into account, following the higher moment analysis.

Figs. 1 and 2
Q. The slide mentions “not satisfy a scaling behavior”. For higher q, there 
is a rising trend of Fq or \Delta Fq vs M^2. When fitting the data to get 
scaling factor, either fitting low M^2 or high M^2 may lead to different 
result?
A. For Fig. 1, because the data do not follow straight line, still they are 
not scaled. For Fig. 2, the scaling is related to low momentum scale which 
corresponds to larger M^2, therefore the fitting range was chosen to be large 
M^2.

Fig. 4
Q. What is the significance of non-monotonicity or dip around 20-30 GeV? It 
seems not so significant.
A. Haven’t tried to calculate yet but PAs will follow up on this.

Q. Data point for 10-40% at 54 GeV is missing, why? (Statistics should be 
fine)
A. Likely forgot to include this point somehow. PAs will double-check.

Q. Why 10-40% is used as a baseline? It’s still close to central events, 
usually more peripheral events like 70-80% is used.
A. Statistically difficult to go for peripheral events, especially for higher 
q. Other interval, e.g. 20-40% will be checked.

Q. Looking at systematic uncertainties for 54 and 62 GeV, why 62 has such 
larger error?
A. slide 21 shows breakdown of the systematic uncertainty.
C. y-axis range is different among panels, difficult to say. Maybe affected 
by statistical fluctuation. Some of data points, e.g. 54 GeV data at track 
cuts = 2 and 62 GeV data at track cuts = 6, have too large error bars 
compared to neighboring data. 
A. These are from fitting. PAs will double-check those data points as well as 
the calculation of systematic uncertainty.

Q. Comparison with theoretical models would be really helpful here. For 
example, UrQMD or any models which don’t include CP.
A. In slide 32, UrQMD calculations for 19.6 GeV are shown. \Delta Fq is 
nearly close to zero in UrQMD.

Q. Critical point was mentioned in the introduction but how one can connect 
the results to CP? 
A. We are looking for scaling behavior as mentioned in slide 6. \nu is 
related to CP. This is the first measurement at STAR.
C. Still not clear what physics message can be delivered. Stating what we 
measured/observed doesn't meet PRL justification. Any theoretical guidance 
(in the plot) may help.