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http://cms.cern.ch/cds/HIN-13-003

Ernesto

Type B

My understanding is that the result on the integrated double ratio is a kind of groundbreaking achievement in the field of the heavy ions physics. In that respect I have few comments on some of the extra results which are presented in the paper.

• it seems that the comparison with PbPb results is suboptimal. We understand the convenience of using for the comparison the results from 2011 data-taking already published by CMS, but given the large uncertainty in translating the “2011” to “2013” results (e.g. the correction factor mentioned at L153 has a 25% uncertainty) one can think that using PbPb results form 2012-13 dataset would substantially improve the quality of the comparison.
• a relevant fraction of the paper (L239-284) is devoted to the discussion of the differential results of Fig.5 but the conclusion is a bit vague. Do you think that this section should be really maintained as such? I would at least shorten the paragraph with the possible interpretations (L270-284) as it has not a firm conclusion.

Type A

Abstract:

It looks a bit strange that what we think is the main result of the paper (the integrated double ratios being smaller than 1) comes after the discussion of the single ratio vs. the event activity.

\|eta_cm|\ < 1.93 → \|eta_{CM}|\<1.93 “CM” is capital case elsewhere in the text

remove double quotes around “event activity”

The cut on the muon pT>4 GeV could be omitted in the abstract

Text:

L5 should the references “[3-5]” be put at the end of the sentence (e.g. after “state” in L7)?

L42 “characterizing Y family” → “characterizing the Y family”

L50-L51 remove “1)” and “2)”

L61 “sensor elements” → “channels” (“sensor” usually indicates the silicon chunk)

L72 “The direction of the higher energy proton beam” → “In pPb collisions, the direction of the proton beam” (“higher energy” suggests we had also asymmetric pp collisions…)

L86 I think it is confusing to quote an “effective luminosity” (4.1pb-1) as the result of some event selection. Just quote the efficiency of this selection (4.1/5.4 isnt't it?)

L92 “the EVTGEN [21] package” → “EVTGEN [21]”

L93 “Final-state bremsstrahlung” → “Final-state radiation” (unless bremsstrahlung is used to indicate explicitly QED radiation

L98 “passing several quality cuts” → “passing the quality cuts”

L123 “center-of-mass colliding energy” → remove “colliding”

L149 “cold nuclear matter”: not being expert of HI physics, this definition comes a bit out of the blue…It could be probably anticipated in the introduction at the beginning of the paper.

L181-185 there is a quite detailed description of the choice of the binning but it is not clear which is the physical motivation for this choice (e.g. the bins do not have the same fraction of events nor there is a simple proportion between the average measures of the event activity in subsequent bins)

L186 “corrected for detector acceptance” I guess to have values integrated in \|eta_CM\|<1.93(and no other restrictions) . If my understanding is correct one should detail it in the text.

L188-189 why the systematic errors on the Y(3S)/Y(1S) fit are twice those on the Y(2S)/Y(1S) fit. In particular 30% syst. refers probably to a single point (pp N_track>31, rightmost “orange” point in Fig.3/right): Can this fit be improved any further?

L193 “midrapidity track multiplicity” could have been introduced earlier

L195-197 and Fig.3 what are the predictions for these trends in absence of the effect you are looking for?

Fig.1 (right): L_int=5.1 pb-1 → shouldn't it be 5.4 pb-1 as in the text?

Figs.2,3,4,5: the title of the y-axis should have “Y(nS)” instead of “Y(ns)”. What is the convention for the boxes, error bars around the data points? Statistical only and total uncertainty?

Fig.4: these plots seems to be a bit overcrowded… Are the Y(3S)/Y(1S) points really relevant for the discussion, since the corresponding data from PbPb are not available?

Stefano

Type B

The paper, to my understanding, presents new effects that deserve the attention of the HI community. However, these new results need to be presented in a much clearer way, especially in the description of the effects we are seeing. The discussions about possible interpretations are hard to follow and not straight to the point. Several paragraphs need to be reworked.

In particular, with respect to readability, the paper would greatly benefit from sectioning. In facts, according to CADI, this work is aimed at JHEP, which recommends sectioning.

In the discussion of systematics related to fitting, nothing is said about the uncertainty on the parameterization of the signal. That is, CB parameters are derived from a fit, with their errors. How is that error reflected in the estimate of the yields and ratios ? Roofit provides the machinery to vary parameters according to their error matrix.

The fits seem to systematically present one or more high points in the valley between the Y1S and the Y2S. Have you tried a double-sided xtal ball ?

Type A

- When printed, figures show a grey-ish background. Please check and in case remove grey background in favor of plain white. Remove “Preliminary”

- Abstract: “Upsilons, which decay into muons of transverse momentum above 4 GeV etc”. Consider something like “Upsilons detected via their mu+mu- decay, in the kinematical region etc …” , or simply “ where both muons have transverse momentum etc.”

- “as a function of two measures of “event activity” ” → no quotes in “event activity”. Consider changing to somewhat like “ studied as a function of event activity”, which in turn is quantified using two observables: etc.. “

- “yields normalized to their event average” - remove “normalized by their event average”: it's in the formula, and can be explained later. I don't know what an “event average” is.

- remove : “different amount of particles accompanying the production of Y”, it's already said in the previous sentence.

- “the ratios .. show a smaller variation” → consider changing to something like “ratios are more stable if measured as a function …”

L18-29: the word “states” is repeated at least 9 times L 34 : “it is noted that … could be accompanying different quarkonium states”. Consider reworking as “it is noted that different quarkonium states could be characterized by distinct event signatures”

L42: “characterizing the Y family” → add “characterizing the production of the Y family ”

L42-54: this paragraph is very important and needs to be written in a clearer and more linear way. Avoid storytelling (“first .. then”) in favor of a more direct approach, f.i. “we have measured single and double ratios of the yields” and then explain exactly what the ratios are.

L49: “corrected to full single-muon transverse-momentum coverage”. Meaning unclear. No hyphen in “transverse momentum”.

L55: “integrated over all event activity”. How does one integrate over “all event activity” ? Seems difficult to integrate over an abstract concept.

L74 :“after 18 nb-1 were taken” → “after an integrated lumi of 18nb-1 was collected”.

L84: “simultaneous collisions” add qualifier (per event, per bunch xing, per trigger ? )

L90 : “Simulated Monte Carlo” : remove “simulated”

L129: “down to a level which is negligible …” → consider replacing with “within our uncertainties”

L130: “to assess the latter” : “latter” refers to .. ?

L135 : “from the above-mentioned signal extraction” → “from the signal extraction procedure described above”

L137 : “two energies ” → “two center-of-mass energies” L140 : “stronger” → more strongly (or something better) L145 : remove “CMS” 154-156: consider shortening by a good amount : “normalized by the lower-statistics pp … in 2011. Normalization to 2013 data was not considered because of the large systematic uncertainties it would imply, due to the different trigger and reconstruction algorithms”.

L169: “the single ratios signal the presence” L171, 172 “one Pb ion .. two Pb ions” → do we really need to specify ?

L181-185: it's not clear why this complicated binning is devised.

L210: Remove “the effect reflects itself” → “The pp sample contains on average two extra tracks per event”. Consider giving right a way a hint to the fact that this is due to feed-down

L204: “one artificially lowers the number” : not understood

L209: “typically assumed feed-down fractions” → “the feed-down fractions retrieved in literature [ref]”

L212: “converted-photon reconstruction efficiency is too low” → “photon conversions cannot account for the observed increase in multiplicity.”

L221: “narrow correlation” → correlation is either weak or strong I believe.

L265: “as well as by the absence of sensitivity of … observable to a modification that is flat versus event-activity” → please rephrase

Giacomo

Type B: The paper presents some new and interesting results, that clearly have a large impact on the HI community as provides important results on the initial state effects estimates. I think such results deserves some further improvement in how they are presented. The flow of the text can be largely improved by rephrasing and reorganizing it. As it is now, there are arguments that are presented, then abandoned and then discussed again in some other part of the article, as well as some repetitions. It kind of looks like a copy-and-paste of different texts. It would be better reorganize the text in some “smoother” way. Some more sectioning (and referencing to the sections inside the text) of the text would as well help the reader, as several topics are discussed.

Type A: 8 “at stages […] bound state,” ⇒ this phrase looks redundant and imo shifts the reader attention from the main point (which is that initial/final conditions can affect the yields as well as QGP)

56 “elsewhere” → “in” 56 “central”→“main”

121 Why is it “conservative”? From the explanation it looks to me that the systematic uncertainty is properly evaluated, and therefore is not conservative. I would remove this adjective, or explain why the systematics is overestimated.

fig. 2: pp markers have a different colour between legend and plot. Should be corrected in the final figure [optional]You may also consider to explain explicitely the arrow in the caption

171-172 Remove ”(one Pb ion)“ and ”(two Pb ions)“. At this point of the paper you used this notation several times already.

169-173 Is there any reference that is worth to add in this paragraph to explain the physical meaning of the single ratio measurement?

197-199 “The Y(2S) … upper limit” This part discusses fig2. I think it will help the reader to move it to before, and if you feel it's really needed put a simple reminder in line 194.

At line 214 you conclude that the decreasing trend of Y(nS)/Y(1S) vs Ntracks can't be explained by selections or feed-down. Then the issue is abandoned until line 270, thus forcing the reader to go back and forth in the paper. It would be better to reorganize a bit the discussion moving lines 270-284 after line 214, or (worst, in my opinion) anticipating in line 214 that the effect is discussed later in the paper if you want to keep it as it is.