STAR Correlations and Fluctuations PWG

[Xin Dong <xdong AT lbl.gov>]

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

On Wed, Mar 9, 2022 at 5:25 PM webmaster--- via Star-cf-l <star-cf-l AT lists.bnl.gov> wrote:

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

Jin Wu (wj2016113394 AT mails.ccnu.edu.cn) has submitted a material for a 
review, please have a look:
https://drupal.star.bnl.gov/STAR/node/58816

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Xin Dong
Nuclear Science Division, Lawrence Berkeley National Laboratory
MS70R0319, One Cyclotron Road
Berkeley, CA 94720, USA
Tel: +1-510-486-4121
Email: XDong AT lbl.gov
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