Hi, We got the referees report on the Stopping paper (see below), and the paper commitee is working on a response taking into account the comments and will resubmit to PRL. The report is rather long, but we think that by including minimum and maximum estimates of the stopping based on putting the remaining baryons ay y=3.5 and y=5.0 we can clearly show that the rapidity scaling is broken. Cheers, Peter -- :-) --------------------------- )-: Peter H L Christiansen pchristi@nbi.dk / (+45)40840492 :-D --------------------------- \-: ---------- Forwarded message ---------- Date: Fri, 20 Feb 2004 20:34:34 +0000 (UT) From: Physical Review Letters <prl@aps.org> To: pchristi@nbi.dk Subject: Your_manuscript LM9682 Bearden Re: LM9682 Nuclear stopping in Au+Au collisions at $sqrt s sub {N N}$=200 GeV by I.G. Bearden, D. Beavis, C. Besliu, B. Budick, H. Boggild, et al. Dr. P.H.L. Christiansen European Organization for Nuc. Res. CERN CH-1211 Geneva 23 SWITZERLAND Dear Dr. Christiansen, The above manuscript has been reviewed by our referees. The resulting reports include a critique which is sufficiently adverse that we cannot accept your paper on the basis of material now at hand. We enclose pertinent comments. If you feel that you can overcome or refute the criticism, you may resubmit to Physical Review Letters. Please accompany any resubmittal by a summary of the changes made, and a brief response to all recommendations and criticisms. Yours sincerely, Christopher Wesselborg Senior Assistant Editor Physical Review Letters Email: prl@aps.org Fax: 631-591-4141 http://prl.aps.org/ P.S. Please ensure that the introduction is accessible to the broad physics audience addressed by Physical Review Letters. ---------------------------------------------------------------------------- Report of Referee A -- LM9682/Bearden ---------------------------------------------------------------------------- I reviewed the manuscript "Nuclear Stopping in Au+Au Collisions at sqrt(snn)=200 GeV" by I.G. Bearden et al. (BRAHMS Collaboration). In this paper the authors report on the measurement of proton and antiprotons over a wide rapidity range (0 < y < 3). While protons and antiprotons at y=0 have been already reported the really new feature of this paper is the extension of the (anti)proton measurement to forward rapidities. Using these spectra the authors derive the net-baryon spectra, and from that, the average baryon rapidity loss considered to be a measure of 'stopping'. In the paper the authors also estimate the total energy loss per participating nucleon, a highly interesting evaluation. The spectra are an important addition to the database of heavy-ion physics. Although they alone do not justify publication in PRL, the studies on stopping and energy loss certainly do. Here, however, I have several serious concerns. As it stands I do not recommend publication in PRL unless the authors address the points below and revise the paper substantially. 1. The presented proton, antiproton spectra and their difference, i.e. the net-protons in fig.1-3 are not feed-down corrected and as such limited in use for comparisons to theory and/or models. Only later in the text when the authors derive the net baryons do they tell the reader that in fact the protons contain ~80% of all protons from Lambda decays (BR(L->pX)/c = 64%/53%). This is a considerable contribution since Lambda/p is close to unity. This needs to be mentioned much earlier and discussed in detail. Clearly, the best solution would be to correct the spectra: There are traditionally two ways to address this problem. Either one corrects the spectra such that they contain *all* feed-down protons below a well defined c*tau (see average hadron. multipl. in hadronic e+e- annihilation events in the Review of Particle Physics), or even better, subtract all known feed-down contributions. The data shown in Fig.1-3 is a mix of both, i.e. only a fraction of the feed-down is contained in the spectra. One has to know the details of the apparatus and the analysis in order to interpret the spectra. I recommend to replace the spectra in Fig. 1-3 by the feed-down corrected ones or plot them in addition to the uncorrected ones. The lambda spectra are published (PHENIX, STAR) at least in 130 GeV Au+Au collisions at midrapidity and found to deviate little in shape from the proton spectra, that is Lambda/p is flat as a function of pt. A feed-down correction can thus be estimated rather easily. 2. The pt spectra are fit with a Gaussian. This is an empirical fit that might describe the data in the measured range well but appears rather unphysical. Whether this distribution is valid beyond the measured range is therefore unclear. What's the reason for the choice of a Gaussian? Typical fit functions with at least some relation to a collective expanding thermal systems are blastwave or Boltzmann. So far both were successfully fit to all proton spectra at RHIC and SPS. T and beta_R from a blastwave fit would be interesting information in itself. By how much do <pt> and dN/dy change when using one of the more physics motivated functions should at least be discussed. 3. On page 6 the authors discuss the corrections applied to derive the net-baryon density. Here the authors entirely neglect the contribution from the Sigma+- decays. The term N_sigma+- is missing in Eq.2. The Sigma+- is so far not measured but its yield is expected to be rather large. In e+e- collisions it was found to be ~2/3 of the Lambda yield and for heavy-ion collisions statistical thermal models predict its yield to be close to that of the Lambdas. The Sigma- decays 100% to neutrons and the Sigma+ 52% to protons and 48% to neutrons. The uncertainty in the yield contributes considerably to the syst. uncertainty. Even more confusing is that the Lambda over proton ratio the authors use to derive the net baryon density (PHENIX collaboration) contains feed-down as described explicitly in ref [19]. In that sense it is misleading to claim Lambda/proton = N_Lambda/N_proton, which implies that this is the ratio of the primary net densities. More discussion on this issue is clearly needed and the uncertainty of the sigma+- contribution needs to be taken into account in the calculation of the systematic uncertainties. BTW: The symbols used for Eq. 2 are very misleading. N_p-pbar is used for the *measured* net-baryons but N_p for the primary net-protons. The latter is usually a notation for the number of lambdas not for the difference (net-lambdas). The whole formalism could be made much clearer by keeping the N_p-pbar (N_n-nbar etc )notation and labeling the measured N_p-pbar with a superscript 'meas.'. 4. The derived rapidity loss is obtained by integrating over the whole rapidity range. It is unclear to me how the authors derive a stopping of 2.0 with a 5% (10%) error when measuring only ~45% of the distribution, especially when the part with the highest weight in the integral is outside of the measured range. While the 'momgaus' distribution is physics motivated the polynomial of 6th appears not justified. I do not see the justification for f(y_p) = 0. The cross-section for diffractive interactions in pp is ~30%! The average Npart for the selected centrality is 357 out of 397 possible participants. I recommend to add curves from models (HIJING, AMPT, etc.) and study the rapidity shift in more detail. I'm very interested in supporting documentation on how the 5% (10%) error was derived. The error here is especially important since the authors make rather strong statements on the violation of the stopping scaling behavior at RHIC. 5. The estimate of the energy loss of the net-baryons is very interesting. In recent presentations (latest at Quark Matter) the authors strengthened their findings by comparing the obtained E-loss with the energy released to the system obtained by integrating their measured pi, K, and p spectra. The inclusion of the agreement of both measurements would strengthen the paper considerably. One could imagine the publication of the identified particle spectra in PRC (which would allow a more in depth discussion of the feed-down issue and correction) and a strong PRL on the issue of stopping and energy-loss, the latter then also compared to the summed energy of the particle spectra. ---------------------------------------------------------------------------- Report of Referee B -- LM9682/Bearden ---------------------------------------------------------------------------- The authors discuss the recent BRAHMS results of proton/anti-proton transverse momentum and rapidity distributions from 200 GeV Au+Au central collisions. They also tried to extract the interesting parameters like mean rapidity shift and energy loss per participant nucleon. In my view this is a very important subject for understand the collision dynamics. However, the conclusion of the paper is based on assumed rapidity distributions that are not covered by the experiment and the information about these assumptions is not provided. This is not acceptable. Here are my comments and suggestions: Let me start with a serious one: The projectile rapidity is ~ 5.4. In the paper, the important conclusions were based on the assumption of the rapidity distributions of net-baryon and <mT> in 3 < y < 5.4 where the experiment does not cover. The measurement only covers the proton rapidity region from 0 to 3. To extract the value of nucleon mean rapidity shift and energy loss, one has to make an assumption on the rapidity distribution of baryons in the region 3<y<5.4. This is what the authors did. However, I found no adequate information, like the functional form and justification about the assumptions have been given in the manuscript. I suggest the authors provide the necessary information and discuss the systematic errors. To make the connection between the energy loss and excitation of the produced system, one could perform the analysis with different collision centralities. I suggest the authors consider this possibility to make the paper really stand out. Details: 1) page 3-1st line-reference [21] is out of place; 2) page 5-3rd paragraph-line 2: replace `the three spectra.' by "the three functional forms."; 3) page 7-Equation 3: dN/dy should be dN(B-Bbar)/dy; 4) page 7-right above the equation, replace `collision E' by `collision' 5) I also suggest the authors list all measured quantities like <pt> and dN/dy for all rapidity bins into a Table. This will be useful for readers to perform their own analysis; 6) Figure 1-y axis label: [GeV^2/c^2] _______________________________________________ Brahms-l mailing list Brahms-l@lists.bnl.gov http://lists.bnl.gov/mailman/listinfo/brahms-lReceived on Mon Mar 1 09:48:40 2004
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