Date: Tue, 25 Jul 2000 15:52:49 -0400 (EDT) From: PR/L-email To: panitkin@sol.star.bnl.gov Cc: prl@ridge.aps.org Subject: lt7333 LT7333 Model-independent source imaging using two-pion correlations in (2 to 8)$A_ Ge Panitkin,S.Y./Ajitanand,N.N./Alexander,J./Anderson,M./Best,D./Brady,F.P. Dear Dr. Panitkin: The above manuscript has been reviewed by our referee(s). 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. Sincerely, Christopher Wesselborg Assistant Editor Physical Review Letters - ------------------------------------------------------------------ Referee A I think that the authors report on a scientifically valid and important research that is of broad interest. The manuscript is well written, clear and interesting. However, before publication, I suggest that the authors consider the following optional revisions, that would improve the presentation. 1) At the end of the first paragraph on top of p.4, the manuscript notes taht the source imaging technique can also be applied `` in other contexts such as proton - proton correlations, where the standard HBT technique cannot be applied." This comment seems to be a real red herring as the standard HBT technique is certainly dealing with bosons not fermions, so it is not relevant to compare with. However, in case of proton-proton correlations, well known methods of Fermi-Dirac intensity interferometry exist and were even used to search for non-Gaussian (donut-like) proton sources. I simply suggest to leave out the last part of this sentence (where the ... applied). 2) Technically, I think the most important shortcoming of the presentation is that it does not mention the frame dependence of the analysis that has been performed, although the formalism and the results are dependent on the frame of the analysis, as evident from the non-relativistic formalism. It is well known, that the Bertsch-Pratt HBT radiii mix spatial and temporal information on the source in a frame dependent manner, and as source imaging is equivalent with the more conventional HBT analysis it must have the same property. However, in the LCMS frame, for high energy heavy ion collisions, the frame dependence is only a second order effect, that is small in the mid-rapidity region. I strongly recommend that the authors specify the frame where the analysis was performed. 3) I suggest to re-plot Fig. 1 by multiplying with a factor of 10, 100 and 1000 the $S(r)$ source functions measured at 4, 6, and 8 GeV, respectively, so that each data point and its error bar could be read off clearly. Similarly, I suggest to re-draw Fig. 3 so that the error bars on the first, third and fourth pairs of data-points could be determined more clearly. I suggest the acceptance of the manuscript after the authors consider the revisions mentioned above. I recommend the publication of the manuscript in the Physical Review Letters. - ------------------------------------------------------------------ Referee B This letter reports the beam energy dependence of the pion freeze-out density at AGS. In this context two approaches are compared. The first uses gaussian source radii obtained from 'conventional' multidimensional Hanbury-Brown Twiss interferometry to derive the freeze-out density. The second uses a method called 'source imaging', where the freeze-out density (or source density) is obtained by an analysis of the one-dimensional (q_inv)-correlation function. The pion freeze-out density and in particular its beam energy dependence is of general interest to the community. Moreover, the freeze-out density is connected to the phase space density, which is a very general quantity in all fields of physics. Also the application of the source imaging method is of interest, in particular in view of the high quality particle correlation data to be expected at RHIC. Therefore, the results presented in this letter are relevant for publication, however, I cannot recommend publication in it's present form. At present I cannot even see whether there is a new and interesting result. In that case a publication as Phys. Rev. Letter would not be justified in my opinion. Before I come to more specific questions, my major point of criticism is the absence of any physics discussion. Neither the results for the pion source density and its implications to the understanding of heavy-ion physics nor the possible origin of discrepancies HBT radii vs. source imaging are discussed. On the other hand the experimental description could be much shorter since it contains no information in addition to what was described already in [16]. Nevertheless, there are open questions remaining that are specific to the data presented and should be addressed here. Momentum resolution: in [16] the fitted source radii were corrected for the finite momentum resolution. How is the finite momentum resolution treated in this letter? This is certainly difficult, because the raw correlation function needed to be treated *before* source imaging, without having a priori knowledge of the source shape. Momentum resolution may alter the shape of the correlation function and make it look more gaussian. This is an important question, because it imposes a limit on the accuracy of the reconstructed source function. What is that limit? The authors are talking about 'useful accuracy out to 20 fm'. How does this relate to the momentum resolution of 3%? What is the resolution in q_inv? Is momentum resolution considered for the Coulomb correction? What is the impact of momentum resolution on the comparison to the source density obtained by the (momentum resolution corrected) HBT parameters? Is it justified to compare a one-dimensional source imaging analysis to results obtained by a multidimensional HBT analysis? Fig.1: Why are the gaussian fits to the q_inv correlation functions not shown? Fig.3: Why is the *inverse* of the source density plotted? The log representation masks the systematical descrepancies, which are of the order 30%. Please use a linear scale, restricted to the region of relevance! There is no point to use a log representation over two decades for data which vary by no more than 50%. What do we learn from the systematic discrepancies? To my understanding the HBT results are corrected for momentum resolution, while the ones from source imaging are not. This appearently decreases the discrepancies, which otherwise would be even larger. How large? The error bars in Fig.1 are similar in magnitude, although the errors of the fitted radii are very different for the two approaches (Table 1). How can this be understood? Also please explain: why are the errors for the 1-dim analysis not much smaller than the errors for the 3 d...(Table 2), if it is the same data set? All Figs: dont use commas in the axis labels Ref.13 never appears in the text. elec_sub.asc revised 7/97 USE ELECTRONIC MODES TO SUBMIT AND RESUBMIT TO THE PR/PRL COMPUSCRIPT PROGRAM Manuscripts intended for the production compuscript-conversion program should be submitted and resubmitted in electronic, not paper, form. Upload via the APS Web-submission site at the URL: http://publish.aps.org/ESUB/, send electronic mail to prXtex@aps.org (where X=a, b, c, d, e, or l for Physical Review A, B, C, D, E or Letters), or mail a DOS-formatted diskette. All of the textual material of the paper (including tables, captions, etc.) should be in electronic form, as a single file. 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