Nuclear Modification Factor of Inclusive Charged Particles in Au+Au Collisions at $\sqrt{{\mathit{s}}_{\mathit{NN}}}$ = 27 GeV with the STAR Experiment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

The draft reads well. I don't have many comments, just a couple of minor ones, below.

Best regards,

 

L28 "ritical" -> "critical".  Same typo at L32

L104-105 It is not clear why "requiring a very large number of hits reduces the quality of tracks " at low pt. I would naively expect the opposite. Please clarify.

Comments on the Quality of English Language

Overall the english is satisfactory in the draft.

Author Response

Dear Reviewer,

Thank you for your comments. I have uploaded the revised version of my manuscript. Please take a look.

L28 "ritical" -> "critical".  Same typo at L32 
done

L104-105 It is not clear why "requiring a very large number of hits reduces the quality of tracks " at low pt. I would naively expect the opposite. Please clarify.
Sentences: Increasing the number of hits in a track improves momentum resolution, but requiring a very large number of hits reduces the quality of tracks with low transverse momentum $p_T$ values.

Answer:
Due to the requirement for a large number of hits, the quality of individual tracks improves, but statistical significance is greatly reduced. There are simply very few tracks of such quality, hence distorting the overall picture.

Best regards, Alisher

Reviewer 2 Report

Comments and Suggestions for Authors

Report of the Referee

Manuscript Ref.: Universe-2840493

Title: "Nuclear modification factor of inclusive charged particles in Au+Au collisions at $\sqrt{s_{NN}} = $ 27 GeV with the STAR experiment"

===========================================================================================

 

The author presented a report on the preliminary results for the nuclear modification factor measurements in Au-Au collisions at RHIC (STAR Collaboration). The starting point is the measure of the transverse momentum distribution of inclusive charged particles for collision energy of 27 GeV for several centrality classes. Using the range of |\eta|<1, the central-to-peripheral nuclear modification factor, R_{CP} is determined. In Fig. 4 a preliminary results for R_{CP}[(0-5%)/(60-80%)] is presented and suppression of particle production at high transverse momenta has been observed. The data description using phenomenological models was not discussed in the report.

 

The paper is well presented and the references are quite adequate. The topic is hot and of interest in the heavy ion physics community. It is a formal report on behalf of STAR Collaboration and the manuscript has the high standards as usual in these cases. 

 

 

For the reasons presented above the paper is clear and well argued. It is suitable in my view for the Universe journal.

 

----

I found only two misprints:

 

Page 1, Lines 28, 32: ritical -> critical.

Author Response

Dear Reviewer,

Thank you very much for your comments. I have uploaded the revised version of my manuscript. Please take a look.

Page 1, Lines 28, 32: ritical -> critical.
Answer: Corrected

Best regards, Alisher

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents new preliminary STAR data on the nuclear modification factor R_CP in 27GeV Au+Au collisions taken during the 2nd phase of the Beam Energy Scan program.

The results are interesting for the community and manuscript is well written, it clearly conveys the message. I have a few questions and suggestions though.

Questions:

1. Regarding the results shown in Fig. 4, are there any model predictions to compare with? The conclusions without those sound a little bit speculative to me.

2. It is mentioned in the conclusions that a suppression cannot be stated from the results. Is it because of the large Nbin uncertainty? If so, it would be good to mention it.

3. In lines 125 and 142 it is mentioned that there is a greater pT coverage and a more accurate characterization. Please specify compared to what, cite the earlier study.

4. In Line 92: velocity is beta (in units of c) and not 1/beta

5. Both N_bin and N_coll are used in the text. Please unify the notation.

6. In Line 110, specify what simulations were used, preferrably with a reference. (GEANT?)

7. In the table: why is Vertex_Z default outside the variation range?

8. also the table: I suggest to convert it to a floating table with caption. I also suggest to use physics variable names instead of technical names, eg. $z_{vtx}$ instead of "Vertex_Z" (similarly for other variables).

9. References 4, 6, 15, 17, 18, 22: Please pay attention to the correct format. Eg. "Gyulassy; Miklos" > "Gyulassy, M" etc.

Comments on the Quality of English Language

Minor suggestions line by line:

before L1: Delete "These authors contributed equally to this work."

L26: "the Lattice" > "Lattice"

L28 and 32: "ritical" > "critical"

Eq.1 and Eq. 2: put a period after the equations.

L50: combination > superposition ?

L59-60: I think "longer" and "shorter" are swapped.

L63 "the jet quenching" remove "the"

L66: "the Cronin effect's enhancement" > maybe "enhancement from the Cronin effect"

L109 "simulation of" > "simulation of the"

L113 "allowed for" > "allowed for the"

L122: I think "spectrum" and "spectra" are swapped. (Plural vs. singular)

L123: "to the" > "to"

L123 rephrase "decrease for more peripheral collisions", eg. "the spectra below for more peripheral collisions in decreasing order."

L134 "The growth of Rcp is seen" > maybe "A growth of Rcp can be observed" ?

 

Author Response

Dear Reviewer,

Thank you for your comments. I have uploaded the revised version of my manuscript. Please take a look.

Questions:

1.Regarding the results shown in Fig. 4, are there any model predictions to compare with? The conclusions without those sound a little bit speculative to me.
Answer: At the time of writing this article, the model data was not yet ready, which prevented us from comparing it with the experimental data. However, we plan to present such a comparison in the future.


2. It is mentioned in the conclusions that a suppression cannot be stated from the results. Is it because of the large Nbin uncertainty? If so, it would be good to mention it.
Answer: Indeed, particle suppression is observed, as described in lines 143-144. However, I believe that the data obtained are insufficient to assert this with absolute certainty.This is associated with significant uncertainties regarding the variable $N_{Coll}$.

3. In lines 125 and 142 it is mentioned that there is a greater pT coverage and a more accurate characterization. Please specify compared to what, cite the earlier study.

Changed to: 
Line 125: From Fig. \eqref{fig:2}, it can be noticed that in the BES-II program, the spectra have a greater coverage in terms of transverse momentum $p_T$ for all centrality classes, in comparison with the spectra of the BES-I programm, which enables a more comprehensive investigation of the nuclear modification factor. 
Line 142: A significant extension to higher $p_T$ values has been achieved compared to the Rcp observed in program BES-I.


4. In Line 92: velocity is beta (in units of c) and not 1/beta
corrected

5. Both $N_{bin}$ and $N_{coll}$ are used in the text. Please unify the notation.
replaced $N_{bin}$ with $N_{coll}$, in fact they are the same, definition of $N_{coll}$ in line 48

6. In Line 110, specify what simulations were used, preferrably with a reference. (GEANT?)
Corrected (Line 109, GEANT-3) 

7. In the table: why is Vertex\_Z default outside the variation range?
Answer: To assess the detector efficiency, Monte Carlo particles were generated with Vertex\_Z < 75, considering the detector capabilities. To account for systematic errors, we did not consider values beyond this criterion.

8. also the table: I suggest to convert it to a floating table with caption. I also suggest to use physics variable names instead of technical names, eg. $z_{vtx}$ instead of "Vertex\_Z" (similarly for other variables).
Corrected (Table-1)

9. References 4, 6, 15, 17, 18, 22: Please pay attention to the correct format. Eg. "Gyulassy; Miklos" > "Gyulassy, M" etc.
Corrected

Minor suggestions line by line:
before L1: Delete "These authors contributed equally to this work."
done

L26: "the Lattice" > "Lattice"
done

L28 and 32: "ritical" > "critical"
done

Eq.1 and Eq. 2: put a period after the equations.
done

L50: combination > superposition ?
done

L59-60: I think "longer" and "shorter" are swapped.
In fact, at our energy levels, spectators quickly move away and do not participate in the interactions of the fireball. Therefore, in collisions with small impact parameters, the produced particles have a longer path than in peripheral collisions.

L63 "the jet quenching" remove "the"
done

L66: "the Cronin effect's enhancement" > maybe "enhancement from the Cronin effect"
done

L109 "simulation of" > "simulation of the"
done

L113 "allowed for" > "allowed for the"
done

L122: I think "spectrum" and "spectra" are swapped. (Plural vs. singular)
done

L123: "to the" > "to"
done

L123 rephrase "decrease for more peripheral collisions", eg. "the spectra below for more peripheral collisions in decreasing order."
done

L134 "The growth of Rcp is seen" > maybe "A growth of Rcp can be observed" ?
done

Please let me know if I missed or overlooked any of your comments, and I apologize in advance for any oversight.

Best regards, Alisher

Reviewer 4 Report

Comments and Suggestions for Authors

In this paper the authors presented the nuclear modification factor of inclusive charged particles in Au+Au collisions at a collision energy of 27 GeV using the new data from Beam Energy Scan Program Phase II (BES-II) of STAR experiment. The new measurements extend the previous BES-I results to higher transverse momentum range, which allows better exploration of the jet quenching effects at low RHIC energies, and may help to understand the effects of the formation and properties of quark-gluon plasma at these energies. As can be seen from Figure 4 of the paper, noticeable suppression of particle production at high transverse momenta is observed. The authors point out that the data is not sufficient to claim the formation of quark-gluon plasma based on this observable, and further study and investigation of the behavior of the nuclear modification factor dependence on energy on the data from  STAR BES-II program are necessary.

It is good to discuss in more details in the paper why the last point of the data at collision energy of 27 GeV (pT > 5 GeV/c, see Figure 2) is bellow 1 whereas the new data (5 GeV/c < pT < 6 GeV/c, Figure 4) are above 1.

Summarizing. I think this paper is an interesting and valuable contribution to the field. The figures and the new data are very informative. The paper is well written and articulated, and once the points raised above are addressed the manuscript can be accepted for publication in Universe.

 

Author Response

Dear Reviewer,

Thank you very much for  your comments. I have uploaded the revised version of my manuscript. Please take a look.

Question:
It is good to discuss in more details in the paper why the last point of the data at collision energy of 27 GeV (pT > 5 GeV/c, see Figure 2) is bellow 1 whereas the new data (5 GeV/c < pT < 6 GeV/c, Figure 4) are above 1.
Added in line 133: In Figure 2, depicting $R_{CP}$ for energy collision 27 GeV with a transverse momentum ranging from 5.5 to 6 GeV/c, it's evident that $R_{CP}$ falls below 1. This discrepancy contrasts with my preceding analysis, where $R_{CP}$ exceeded 1. The variance is attributable to the influence of pseudo-rapidity on $R_{CP}$. Specifically, in my analysis, pseudo-rapidity is set at 1, whereas in the previous one, it stood at 0.5.


Best regards, Alisher

Reviewer 5 Report

Comments and Suggestions for Authors

In this paper, the nuclear modification factor R_CP for Au+Au collisions at a collision energy of 27 GeV at the STAR experiment was presented up to the transverse momentum of about 10 GeV, and jet suppression was observed for the first time at this collision energy.

The paper is well written, and I recommend the publication of this manuscript in the Journal of Universe. I have one comment regarding the last sentence of this paper. Hydrodynamics alone cannot address the high pT particles. Therefore, I recommend modifying the term 'hydrodynamic models' to 'hydrodynamic model with the propagation of non-equilibrium high-energy jet approach.'

Author Response

Dear Reviewer,

Thank you very much for your comments and recomendation. I have uploaded the revised version of my manuscript. Please take a look.

I modifed the term 'hydrodynamic models' to 'hydrodynamic model with the propagation of non-equilibrium high-energy jet approach.' in line 152

Best regards, Alisher

Reviewer 6 Report

Comments and Suggestions for Authors

The authors present a measurement of the nuclear modification factor R_CP for gold on gold collision at a nucleon-nucleon center-of-mass energy of 27 GeV obtained by analyzing data from the  STAR experiment at RHIC. This improved p_T spectrum enables a more accurate characterization of the medium modifications occurring in high energy charged particle production, and notably a significant suppression at high p_T is observed. These measurements can be compared with viscous hydrodynamics simulations which help to reveal the dynamical behavior of the quark-gluon plasma phase.

The following minor points should e addressed before publication:

The authors cite ref.[13,14], but the existence of a first order phase transition with a critical end-point in the QCD phase diagram is still very controversal. Predictions come from quark models, whereas QCD lattice simulations are not feasible at large mu_B due to the sign problem. 

On page 1, correct ritical to critical (twice)

Caption to Fig. 1: explain FTX as fixed target...

page 4: the speed of charged particle, denoted as \beta c,... 

page 5:    The spectra are shown... Each set of data was mutliplied by a power of 10 for better visibility.

 

Comments on the Quality of English Language

English language is fine.

Author Response

Dear Reviewer,

Thank you for your comments. I have uploaded the revised version of my manuscript. Please take a look.

Questions:
1.The authors cite ref.[13,14], but the existence of a first order phase transition with a critical end-point in the QCD phase diagram is still very controversal. Predictions come from quark models, whereas QCD lattice simulations are not feasible at large $mu_B$ due to the sign problem. 
Answer: To address this question, I am currently conducting my own research.

2.On page 1, correct ritical to critical (twice)
Corrected

3.Caption to Fig. 1: explain FTX as fixed target...
Corrected 

page 4: the speed of charged particle, denoted as $\beta$ c,...
Corrected (Line 91-92)

4.page 5: The spectra are shown... Each set of data was mutliplied by a power of 10 for better visibility. 
Corrected (Line 122-124)

Best regards, Alisher