STAR Flow, Chirality and Vorticity PWG

[Prithwish Tribedy <ptribedy AT rcf.rhic.bnl.gov>]

Dear Shengli and PAs,
  Sorry for the delay in providing comments on small system paper:
https://drupal.star.bnl.gov/STAR/system/files/STAR_small_system_short_paper-6_0.pdf

Congratulations to the PAs for getting this challenging analysis to the 
final phase. I’ve received comments from a few people and here are 
compilations that are mostly form Wei Li and myself.

Overall, we’re glad that results are in a very good shape, including 
comparison with several models.

-Despite of many papers from Phenix on this topic — this paper STAR 
brings something very important to the community. However, we feel this 
fact is not very well emphasized. Here are a few comments that may be 
worth pointing out :
This STAR paper brings in mid-rapidity measurements that are necessary, 
most of the theory calculations/models that has driven RHIC small system 
scan are boost invariant. In order to test the predictions — precision 
mid-rapidity measurements are needed. I think — a point along this line 
should be in the abstract and introduction (if possible). Before going 
to sub-nucleonic fluctuations etc. (which is best suited for the 
conclusion part) at the early part of this paper it’s worth to mention 
that this measurement brings in a critical test of shape engineering 
driven by nucleon degrees of freedom (the original proposal of RHIC 
small system scan). Later on we can say whether the results agree with 
such predictions or not.

-The paper written as it is now is way too technical for PRL. In 
particular, the title, abstract and introduction require significant 
improvements. For example, "Measurements of v2 and v3 ..." cannot be 
understandable to general readers. At least, it should be said like 
"measurement of azimuthal anisotropy". First sentence of abstract "... 
extracted by three kinds of subtraction methods ... |Δη|>1" is way too 
technical. Second paragraph already shows a table without even defining 
ε_2, ε_3 etc. v2,v3 are never defined. There are too many jargons all 
over the place. In general, the paper will benefit from some editorial 
supports.


- Introduction completely ignores all previous small system results from 
LHC and RHIC, while using discovery of QGP in AA as the motivation. This 
is not appropriate. There should be a review of established knowledge of 
flow in small system.


- Related to the previous comment on why we do non-flow subtraction. 
Somewhere while introducing  template method and other approaches we 
need a statement to justify why we’re doing this. Several papers have 
critically reviewed the template method — this cannot be ignored. A 
comment is needed. Some papers say “closure fails” — what is our 
response to that? One point to mention is that such studies have model 
dependence as flow/non-flow is different between the models.

Another point worth mentioning: The recent Jamie et. al. paper has shown 
raw results are all over the place, with template method (although they 
say it fails closure) the results become similar to what STAR finds.


- l37-43: here we speculate that PHENIX results may be affected by 
non-flow, flow decorrelation but it doesn't make the case how STAR can 
do better. I would suggest using different phase space coverage as a 
main motivation for new measurements from STAR, which may have different 
sensitivity to non-flow, rapidity dependent flow decorrelations. Keep in 
mind that the chance of getting a referee from PHENIX is very high.

- Since PHENIX has published their results long ago, and recently 
submitted a new paper standing by their results, we cannot pretend that 
they do not exist but have to somehow address the comparison with 
PHENIX. If space is limited, at least it should be done in the 
supplemental material and comment in a paragraph in the main texts. 
Based on recently small system task force, the conclusion is that the 
difference is likely to be physics related, because of different methods 
and detector phase space coverage. Following that line of arguments will 
help get our paper accepted. What is new from STAR is a different phase 
space region which may have different sensitivities to non-flow, 
rapidity dependent decorrelation, nucleonic vs sub-nucleonic scale 
fluctuations. It is unlikely we can get away from this.

Specific suggestions along this line of comments:
Strong acceptance dependence is shown by Phenix paper (this point cannot 
be ignored at all). The shape engineering based on nucleon d.o.f does 
not work if acceptance changes. Raw v2 ordering from Phenix without 
non-flow correction are also inconsistent with shape engineering 
results, v3 becomes imaginary. Therefore STAR measurement at a different 
acceptance (mid-rapidity) is crucial. Also, a proper non-flow treatment 
is crucial. We think this should be regarded as a strength and the 
starting point of the paper.


- there are lots of discussion of flow, non-flow but again, the problem 
is that introduction doesn't do a good job to introduce all those terms.

- I think our statement on subnucleonic fluctuation is too strong. While 
it is true that ratios between different species in Fig. 4 agree better 
with sub-Glauber, IP-Glasma with subnucleonic fluctuation does not 
describe v2 data in Fig. 3. and superSONIC without subnucleonic 
fluctuations but pre-flow can also describe the data. So it is too early 
to definitive conclusion.


-Why same multiplicity in p+Au is a choice — not emphasized. Is it to 
keep the non-flow and its multiplicity dilution same between p+Au and 
d+Au ? Similar argument is given by PHENIX to choose BBCS-FVTXS-CNT and 
not BBCS-CNT-FVTXN due to lowering of multiplicity in the 
proton/deuteron/He side. Something along this line can be mentioned.

Best,
Prithwish




On 2021-08-08 16:19, Wang, Fuqiang wrote:
> Hi Shengli, All,
>
> I'm attaching my comments as pdf as I have some equations in the
> comments. But my main issue is about the omission of near-side jetlike
> peak normalization method for nonflow estimation. I see that you've
> done the work in the analysis note, but it's completely ignored in the
> paper. Why?
>
> Best regards,
> Fuqiang
>
>
>
> > -----Original Message-----
> > From: Star-fcv-l <star-fcv-l-bounces AT lists.bnl.gov> On Behalf Of 
> > Prithwish
> > Tribedy via Star-fcv-l
> > Sent: Thursday, August 5, 2021 1:50 PM
> > To: Shengli Huang <shengli.huang AT stonybrook.edu>; STAR Flow, Chirality 
> > and
> > Vorticity PWG <star-fcv-l AT lists.bnl.gov>
> > Subject: Re: [Star-fcv-l] The small system flow for PWG review
> >
> > Dear FCV folks,
> >    This is a high profile paper from STAR. I would urge you take some 
> > time to read
> > the manuscript and send your comments no later than early next week.
> > Best,
> > Prithwish
> >
> > On 2021-08-02 10:32, Shengli Huang via Star-fcv-l wrote:
> > > Dear All,
> > >     You can find the updated draft of small system flow after PWGC
> > > comments below:
> > > https://drupal.star.bnl.gov/STAR/system/files/STAR_small_system_short_
> > > paper-6_0.pdf
> > >
> > > BTW: PWGC comments can be found here:
> > > https://lists.bnl.gov/pipermail/star-fcv-l/Week-of-Mon-20210329/000730
> > > .html
> > >
> > > Your comments are welcome!
> > >
> > > Thanks!
> > > Shengli
> > > _______________________________________________
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