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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) really relevant for the discussion, since the corresponding data from PbPb are not available?