Measurements of J/ψ Production vs. Event Multiplicity in Forward Rapidity in p + p Collisions in the PHENIX Experiment
Round 1
Reviewer 1 Report
The author presents new preliminary results from the PHENIX experiment on the self-normalized multiplicity-dependent yields of the J/psi mesons in 200 GeV pp collisions. There is a stronger-than-linear growth of the yields with multiplicity, that is usually attributed to multiple-parton interactions. The analysis investigates for the first time the impact of auto-correlations by subtracting the contributions of the decay-muons to the multiplicity. The results contribute to the understanding of complex vacuum-QCD processes in high-multiplicity pp collisions, and aid model development. I assume the analysis underwent the scrutiny of the experimental review process and the scientific content is sound.
It has to be noted, however, that the article is not very well written. While it is relatively easy to follow, its style resembles an internal note rather than a publication.
Questions:
1. Does the analysis use prompt J/psi-s, i.e. is there a correction for B->J/psi+X etc. processes?
2. Autocorrelation is accounted for by removing the dimuon from the multiplicity. This does not remove the contributions from ccbar-emitted extra gluons, or those coming from a parent B (if feed-down is not corrected for). Do you have an estimate how big these effects are?
3. Why is the mass peak in Fig1 right about 60% higher than Fig1 left? My understanding is that the setup is symmetrical.
Comments/questions line-by-line:
L6 and L28: what do you mean by "scales", scales of what?
L65: In my view, MPI is not "different" than traditional pQCD but accounts for additional processes, eg. secondary hard processes or multiple scatterings, while typically only the leading hard process is calculated with pQCD. I would rewrite or just remove that sentence.
L99: is the pT-spectrum relevant here?
L106: what do you mean by 'some efficiency corrections'? Could you please specify?
L262-282: This list is probably too detailed for the average reader and relies on internal variables that need some explanation. I suggest not to use text variable names (eg. Evt_vtxZ) and introduce a regular variable instead ( z_{vtx} ).
The chi^2 quantities should be explained, the reader has no idea what quantity is checked against what hypothesis. Similarly to vertex probability.
L285. I belive that it is not told anywhere what pseudorapidity ranges the N_ch values correspond to.
L294: Maybe it would be worth saying that the asymmetric CB function is used to account for the bremsstrahlung tail.
Figure 1. is tagged as "PHENIX". Is this label correct? Are those plots final, preliminary or technical?
L322: I do not understand how the stat. errors of the 1st bin can be used as global systematics, and why is the 1st bin Nch=1. Could you pls. elaborate?
L378: I disagree that the precision would be comparable to ALICE. The reach maybe, but the error bars are at least 3 times bigger. I suggest to rephrase it.
L387: Reference Fig. 5 missing from the paragraph.
L389 pThat should be defined, the cutoff value should be given. Can it cause a bias in the sample to use a pThat cut?
L403: I believe the second y should be eta
The language of the paper should be improved. In the following I mark some examples, however, this is not an exhaustive list by far.
L53 is call > is called
L106 efficiencies corrections > efficiency corrections
L110 is also scaled > is scaled by, or scaling with?
L118 addition > additional
L274 hits on > hits in
L294 Crystal ball > Crystal Ball
L389: setup > set up
L393: setup > setups
L406: in the same rapidity > at the same rapidity
L417 partons > parton
L424 jet > jets
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This work reports on J/ψ production at RHIC in excess to the perturbative expectation based on single-parton distributions (p + p data at √s = 200 GeV), detected by PHENIX. This excess is interpreted as an effect due to multi-parton interaction judged by PYTHIA simulations.
This is very interesting work which sets the stage for future data analysis of J/ψ production events from p+Au and Au+p collisions and performs good comparisons with LHC data.
Therefore, I recommend this paper for publication in Universe after the following minor language issues have been resolved:
l. 186 -> calorimeter
l. 167 -> different production processed compared to ...
l. 190 -> and
l. 344 -> gathered
l. 351 -> inelastically
Pls let a native speaker go through the ms to spot more of these little mistakes.
Publish after minor revision.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
This paper, presented by Dr. Z. Shi on behalf of the PHENIX Collaboration, is very valuable for those who are interested in this field. The introduction is a good review of the history of J/psi production at high energy.
The author shows several experimental data, and compares them with PYTHIA simulations.
It is nice and kind for the readers if the author writes what is the new finding in this field.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The Authors addressed all my comments and significantly improved the manuscript. I recommend it for publication in the Universe special issue.
