STAR HardProbes PWG

["Ma, Rongrong" <marr AT bnl.gov>]

Hello Nihar

Out of interest, I read through your very nice paper, and have some comments 
for your consideration. 

===== Main comments =====

I feel the main selling points of the paper are that we observe evidence for 
medium response in terms of acoplanarity broadening at RHIC, and that model 
calculation (JEWEL) that can describe LHC data is not able to reproduce our 
results. The abstract says "providing new insight into jet quenching 
mechanism" and "compared to theoretical calculations", which is a bit weaker. 
I think we should make stronger, more physics-related statements. 

line 73: are the previous results of no medium-induced broadening consistent 
with the observation in this paper? If so, how? I think some words need to be 
said about this in the paper. 

line 180: there seems a linear rise in SE/ME ratio in the normalization range 
for R = 0.5 jets. Have you quantified the significance of this rise? 

line 258-259: since the p+p baseline is from fitting in this case, I think 
you need to spend a few more sentences to describe in detail how the fitting 
is done, how the value in each bin is determined from fit function and what 
the uncertainty of the procedure is. 

line 259-261: this sentence reads like we are not confident about our 
results. It is expected that we have done these cross checks before 
submitting the paper. I suggest to remove the sentence. Speaking of the cross 
checks, I compared Fig. 3 to Fig. 2 of 2309.00156, and found some potential 
inconsistencies. 
- For pi0 triggers and recoil jets of 15 < pT,jet <20 GeV/c and R = 0.2, I_AA 
values are below 0.2 for 2.6 < \Delta\phi < 3.14 in this paper. In I_AA vs. 
pT (Fig. 2 of 2309.00156), I_AA is always above 0.2 in this range. Do we 
understand why? I am not sure how much one can attribute the difference to 
the statistical and systematic uncertainties since they are from the same 
datasets, so the uncertainties should be highly correlated. 
- For gamma triggers and recoil jets of 15 < pT,jet <20 GeV/c and R = 0.2, 
I_AA values for the two largest \Delta\phi bins having most of the recoil 
jets are about 0.3 and 0.6, with the 0.6 bin containing more yields. In I_AA 
vs. pT plot, I_AA in this pT range is about 0.3. 
- Fig. 3 of this paper shows results for gamma trigger and recoil jets of R = 
0.2 and 10 < pT,jet < 15 GeV/c, while Fig. 2 of 2309.00156 stops at 12.5 
GeV/c for I_AA vs. pt. This is probably just binning, but on the face value, 
they are inconsistent. 
I tried to look into the AN about the consistency check between the two 
analyses, but could not find any. I think it will be useful to add such 
studies to AN for all jet R and pT bins. 

line 307-312: is it possible to discuss, or even speculate, why JEWEL can 
describe LHC results, but not RHIC? What physics might be missing? I think 
such a discussion will greatly strengthen the paper. 

===== Minor comments =====
line 7: I think the trigger E_T range is 11 - 15 GeV, not 9 - 20 GeV.

line 45: there are no ATLAS papers cited in [22-34]. People might complain 
about this. 

line 112: "global tracks" is a STAR term. Need to explain it or avoid using 
it.

line 112: the "15% highest" refers to multiplicity distribution after trigger 
inefficiency correction, not the raw distribution. Is this what you have in 
mind?

line 217: I think you need to introduce the used bin widths before stating 
here the bin widths are large

line 222: it might be useful to put the weight matrix for \Delta\phi in 
appendix. Since the correction seems substantial for R = 0.5 jets, you may 
consider comparing results before and after \Delta\phi smearing correction in 
the appendix. 

line 241: it is a bit hard to see "falling \Delta\phi distribution and larger 
yield" by eye in Fig. 1. Also, it is not clear to why this sentence is 
needed. We should have vetted our results thoroughly even if the features are 
generated through corrections. This sentence sounds like we are not very 
confident about the results. 

Figs. 2 & 3: it will be useful to mention briefly in the text how the 95% 
limits are obtained

Hope these are helpful. Thanks. 

Best
Rongrong

> On Apr 7, 2024, at 10:16 PM, Nihar Sahoo via Star-hp-l 
> <star-hp-l AT lists.bnl.gov> wrote:
> 
> Hello HP-pwg,
> 
> We have finalized STAR gamma+jet and pi0+jet acoplanarity paper draft.
> Paper draft, analysis Note, and paper webpage can be found below.
> Please send your comment and feedback.
> We request to form GPC.
> 
> Paper draft:
> https://drupal.star.bnl.gov/STAR/system/files/AcoplanarityPaper_v1.pdf
> 
> Analysis Note:
> https://drupal.star.bnl.gov/STAR/system/files/AcoplanarityAanalysisNote_V0_0.pdf
> 
> Paper webpage:
> https://drupal.star.bnl.gov/STAR/blog/nihar/Paper-webpage-Measurement-direct-photonjet-and-pi0jet-azimuthal-correlation-AuAu-and-pp-c
> 
> 
> Thank you
> PAs (Nihar, Derek, Saskia, and Peter)
> 
> 
> 
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