Dear Dr. Wesselborg,

We have received your message including the referees’ reports on our manuscript:

LQ9030
Evolution of the nuclear modification factors with rapidity and centrality in ${d}$+Au collisions at $\sqrt{s}_{ {NN} }$=200 GeV
By: I. Arsene, I.G. Bearden, D. Beavis et al.

We thank your referees for the thorough reading of our paper and note first that both assert the paper warrants publication in Physical Review Letters.   

Secondly we note that Referee B’s observation that the ratio in figure 2 for eta = 3.2 (the rightmost panel) is not consistent with the spectra presented in figure 1 (the rightmost panel) is indeed correct.  After careful checking of the data that went into making those figures we found that the p+p spectrum used to make the RdAu ratio in figure 2  (last panel) was not the same as the one displayed in figure 1, which was mistakenly taken from an earlier analysis. We then thought it appropriate to completely review the methods and the cuts used in the analysis, and also undertake an independent analysis of the p+p spectra at eta=3.2, since it is this spectrum that was presented erroneously in figure 1.    The main conclusion of this review is that the nuclear modification factor RdAu at eta=3.2 has changed slightly and within statistical fluctuations, but its overall features remain the same, and the spectra shown in figure 1 at eta=3.2 have been replaced with ones from this improved analysis.   This extensive check of our analysis allows us also to update our estimates of the systematic and statistical errors allocated to the invariant yields at forward rapidities.  

Importantly Figures 2 and 3, that embody the essential results of the paper, are substantially unchanged and the physics conclusions remain the same.  Consequently we are resubmitting the paper with the changes summarized below.  

                                                                       Respectfully, 

                                                                       R. Debbe (For the BRAHMS Collaboration)

Summary of Changes – Omitting minor syntactical changes

To avoid repetition, all changes to the text are listed only once and referred to in the subsequent detailed replies to each referee. 

1) We have corrected the panels corresponding to eta=3.2 in figures 1 and 2, the spectra shown in figure 1 are now the correct ones, the ratio at eta =3.2 shown  in figure 2 is calculated from the spectra shown in figure 1 and it has changed   within statistical fluctuations but its overall features remain the same. All other results remain unchanged.

2) The extensive check of our analysis allows us also to reduce the statistical errors at eta=2.2 and 3.2 and update the systematic errors allocated to the invariant yields at eta= 3.2.
The new analysis indicates the value of the assigned systematic error in the pt ranges where field settings overlap should be increased, leaving the previous value of 15% unchanged in the other ranges. After the sentence on page 2:
".....have been applied, the 15% systematic errors ... from these effects." we have added:
"However, at the boundary between field settings at 4 degrees (between 1 and 2 GeV/c), the systematic error is 20%."

3)For the benefit of the general PRL reader we have added the following sentence at the end of paragraph 2.  “At RHIC energies and at mid-rapidity the saturation scale for Au ions is expected to be ~ 2 GeV2  [6-8]”. 

4) In order to clarify the description of our analysis we added the following statements to page 2:
"The top panels show the outline ......” becomes
"The top panels show the outline of the corresponding data samples for the employed settings in terms of eta and transverse momentum pt, with the eta range of each measurement shown with dotted horizontal lines.”

5) The caption to Fig 1 has been changed:
" Top row: ....   " to:
“Top row: Outline of the data samples in eta vs pt collected with the ....".  And an explanatory line has been added  “… (shifted in eta), gray lines are used to indicate the overlap of the settings.”

6) In the same paragraph, after ".... , and is corrected for the spectrometer acceptance and tracking efficiency." we have added an additional sentence:
" .... , and is corrected for the spectrometer acceptance and tracking efficiency. The Forward spectrometer acceptance ranges from 2 to 4% and is known with an accuracy that ranges from 3 to 5% of those values."

7) Also on page 2 we changed:
"No corrections for the finite momentum resolution, absorption or weak decays have been applied" was changed to:
"No corrections for the finite momentum resolution, binning effects, absorption or weak decays have been applied"

8) Paragraph 2 on page 3 last sentence, "There in a strong correlation…." has been changed to:  "The values of the RdAu ratios at low pt are observed to be similar to the ratio of charged-particle pseudorapidity densities…"

9) The last sentence of paragraph 2 of page 3 has been modified to read:  “ The functional form and the value of alpha of the central-to-peripheral ratio is remarkably close to that of the saturation scale, Qs2   extracted at HERA  (Ref 5).” 

10) At the suggestion of both referees to avoid theoretical bias, we have changed the last paragraph following the first sentence:
“This suppression, which is absent at mid-rapidity [10, 22] increases smoothly with pseudorapidity, i.e. as the difference in rapidity between the detected particles and the gold ion increases.  Also, the change from mid- to forward rapidities is stronger for central collisions than for semi-central collisions, indicating a dependence on the geometry of the collisions.  Such effects are consistent with the onset of saturation in the Au nuclei gluon density at small-x values that modifies the shapes and magnitudes of the RdAu ratios at all transverse momenta.
The results presented in this Letter have generated strong interest in forward physics and the possible relevance of these measurements to the onset of saturation at RHIC.”