STAR Correlations and Fluctuations PWG

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Dear star-cf-l AT lists.bnl.gov members,

Xin Dong ( xdong AT lbl.gov ) has commented on a material originally submitted  
by Jin Wu ( wj2016113394 AT mails.ccnu.edu.cn ) at
https://drupal.star.bnl.gov/STAR/presentations/Quark-Matter-2022/Measurement-Intermittency-Charged-Particles-Au-Au-Collisions-sqrts-0

Comment:
Hi Jin,

I was asked by Rongrong and Tafafumi to review your nicely prepared QM poster 
 
draft. Please find my comments/suggestions below.

1) General comments:
      a) Slide 2-5, in the title, you have some numbers in the front which I  
assume you try to indicate the ordering. I see this is redundant since you  
have page numbers at the bottom and as it has no separation from the rest  
text, this may cause some confusion. e.g. Slide 3, it may read like 2*F_q  
etc.
      b) you may save the foot region on each slide to give your space on 
each  
slide. The left and middle texts are not necessary, you may just leave the  
page numbers on the bottom right corner.
      c) In all the figures on Slide 3,4,5, please label (pT, eta) region of  
this analysis.

2) Slide 1
      a) Third sentence, "The scaling exponent is related to the critical  
component ..". I am not sure what you mean by "critical component" here? I  
find this part is not needed, since in the next sentence you mention the  
potential relation to the CP search. I would suggest dropping "is related to  
the critical component and".
      b) Third line from bottom, my understanding is the analysis is for  
charged particle at |eta|<0.5. This should be also mentioned here.
      c) The abstract ends with the observations, but doesn't contain any  
physics message (see my comment to the last slide)

3) Slide 2
      a) Right figure, need a title on what distribution this is (presumably  
particle density distribution within one single event (what event,  
real/model)). Need units for (X,Y)-axis titles.
      b) Second bullet, for completeness, need to define n_i.  And for M_D, 
is  
the current analysis done in 2D (px,py)? If so, you can simplify by removing  
the superscript D and explain how the 2D space is partitioned.
      c) One technical question on the calculation for my own understanding,  
what if (n_i-q+1)<=0, so the contribution from this cell will be zero or do  
you truncate? In the case of M sufficiently large, all cells will have only 1 
 
or 0 tracks, for q>=2, will F_q turn to zero? In the case of M=1, for  
mixed-event, shall I expect F_q to be 1?
      d) Analysis techniques:
             i) Hadrons? Did you do particle identification? Or is the  
analysis done with all charged particles? Then we need to be precise here.
             ii) Centrality:  presumably, these are "uncorrected" charged  
particle multiplicity.
             iii) Can you elaborate how the mixed event is constructed? Shall 
 
we call "to remove backgrounds" or "to estimate statistical contribution"  
(one is interested in the dynamic contribution)?
             iv) For interested particles, what is the pT region and how the  
space is partitioned, in (px,py) or (pT, phi)?
              v) The analysis is done within each centrality bin or each  
multiplicity bin and then averaged within the centrality? In either case, how 
 
the finite centrality bin width effect is considered in this analysis?
             vi) Efficiency correction, the observable is looking at the  
fluctuation with the local momentum bin. However, if two or more tracks have  
very close momenta, I am worried that they may be reconstructed as one merged 
 
track (clusters in TPC merge). I don't know how our efficiency correction  
takes this into account.

4) Slide 3
       a) Please also label the (pT, eta) region.
       b) What is the reason for the X-axis starting from ~100? Why not start 
 
from 1?
       c) It seems all distributions seem to jump up a bit at 2nd, 5th, 8th  
data points for all energies? Is there any reason for this?

5) Slide 4
       a) in both top and bottom figures, Y-axises are missing the labels for 
 
scales.
       b) bottom figure, data points in the first panel have uncertainties  
along the X-axis, but not in other panels? Any reason?
       c) I would strongly recommend adding a figure showing beta_q vs. q  
which you use to extract the exponential quantity which is the key quantity  
nv.
       d) top right formula, you introduced DeltaF_q ~ (M^2)^phi_q, but 
didn't  
discuss phi_q?
       d) The two statements in the bottom.
               i) first bullet, first, not sure what you mean by  
"DeltaF_q(M)/M scaling function". Second "DeltaF_q(M)/M scaling behavior is  
observed but not strong." I don't quite follow what scaling behavior you mean 
 
here. The top figure shows dF_q vs. M^2, it increases slower than a linear,  
but not clear about the exact relation.
               ii) second bullet, as commented in (c), we need beta_q vs. q 
to  
illustrate this point.

6) Slide 5
        a) As I mentioned in the General Comment, please label (pT,eta)  
regions on each figure.
        b) Right figure, I understand you want to scale up some energy data  
points so they can be separated, but the choice of these scaling factors  
seems too random. The point here is you want to illustrate the centrality  
dependence. I think you can make a six-panel figure for energies from 19.6 -  
200 GeV (low energies don't matter here), and you don't need to apply a  
scaling factor for each panel.
        c) On the physics discussion, are there any model calculations one 
can  
compare to? Hijing, AMPT or UrQMD? If not available, I would still need to  
add a bullet point to comment on the to-do studies, something like "Model  
studies to understand the baseline for the extracted quantity nv etc.". On  
the analysis side, I think we need to perform the Model + GEANT studies to  
understand the impact of the detector effect on multiplicities in the local  
momentum bin as I commented in 3-d-v.

Thanks and Best Regards

/xin


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