Date: Wed, 12 Apr 2000 14:20:33 -0400 (EDT) From: PR/L-email To: RLACEY@sbcha1.chem.sunysb.edu LP7672 Antiflow of $K sub s sup 0 _ mesons in 6$A_ GeV Au $ + _ Au collisions Chung,P./Ajitanand,N.N./Alexander,J.M./Anderson,M./Best,D./Brady,F.P./Ca Dear Dr. Lacey, The above manuscript has been reviewed by our referee(s). We ask you to consider the enclosed comments from the report(s). While we cannot make a definite commitment, the probable course of action if you choose to resubmit is indicated below. ( ) Acceptance, if the editors can judge that all or most of the criticism has been met. (X) Return to referee B for review if available. ( ) Submittal to new referee(s) for review. Please accompany any resubmittal by a summary of the changes made, and a brief response to all recommendations and criticisms. Sincerely, Jerome Malenfant Senior Assistant Editor Physical Review Letters ------------------------------------------------------------------ Referee A Manuscript Number: LP7672 Author: P. Chung, ... Title: "Anti-flow of K0s Mesons in 6 AGeV Au+Au Collisions" The paper reports the results of K0 directed flow measurements at the AGS energies. This is the first measurement of K0 flow at 6 AGeV. K0 directed flow is very sensitive to the in medium kaon-nucleon potential and thus provide very important information about dense nuclear matter. The manuscript is well and clearly written. I recommend the paper for the publication in the Physical Review Letters. ------------------------------------------------------------------ Referee B Manuscript Number: LP7672) Author: P. Chung et al. Title: Antiflow of K^0_s mesons in 6A GeV Au+Au collisions The manuscript "Antiflow of K^0_s mesons in 6A GeV Au+Au collisions" by P. Chung et al. presents new data on the asymmetry of the azimuthal emission pattern of kaons in nucleus-nucleus collisions. Such a feature is predicted by transport model calculations as a consequence of the kaon mean-field potential which influences the kaon in-medium propagation. The paper is well written and the reported results represent a significant progress in the field of heavy ion physics. The authors suggest that the observed anisotropy of kaon emission is caused by a repulsive kaon-nucleon potential. This interpretation relates the presented data to an important issue of current research which is the modification of hadron properties in dense nuclear matter. In this sence the paper is of broad interest, in particular for astrophysics. However, the interpretation proposed by the authors is not unique. An antiflow pattern was also found for pions in Au+Au collisions at AGS energies and explained by the rescattering of pions at the spectator fragments. This aspect is treated in the paper only by showing the RQMD calculation including rescattering without in-medium effect. I would appreciate a more thorough and model-independent discussion based on experimental data, namely the comparison of kaon and pion (anti-)flow in Au+Au collisions at 6A GeV. At high pion momenta (above the delta resonance) the pion-nucleon and kaon-nucleon scattering cross sections become almost similar, and a repulsive kaon-nucleon potential would result in a more pronounced antiflow signal for kaons than for pions. The authors should add a discussion on this question and - if possible - show a comparison of kaon and pion flow. Accordingly, the argumentation given in the abstract ("This observation suggests ...") is too simplistic. It was found that the strength of the pion flow depends both on the impact parameter of the collision and on the transverse momentum of the pions. Similar effects are expected for kaons. Therefore, an important information needed for the interpretation of figure 3 is the low cutoff of the kaon transverse momentum (p_T). This information should be given in the paper. Moreover, the theory curve shown for comparison should be produced with the same lower cutoff value. I suspect that the kaon identification efficiency is strongly p_T dependent. The displacement of the kaon decay vertex from the reaction vertex depends on the kaon momentum. Hence, low p_T kaons decay in a region of high track density where the kaon efficiency is reduced. The fact that the bulk of the kaons has a wrong decay length (see left part of figure 2) may be caused by this problem. It is not clear to the reader whether the value of the kaon flow as shown in figure 3 is representative for the bulk of the kaons or only for a subsample. A way to avoid this problem is to show (or at least to describe in words) the p_T dependence of kaon flow. This information is obviously available (because it was used to correct ) but not shown for reasons not clear to me. If the measurement is of good quality, the p_T differential flow is even more informative than the momentum averaged value. If this is not the case, then the efficiency correction for is probably much larger than the given estimate of 10%. These questions should be addressed in more detail. Another important piece of information is the impact-parameter dependence of kaon flow. The authors mention only a similarity of the antiflow patterns for more central and less central events. Does this mean that there is no impact-parameter dependence of the kaon flow? This question deserves a clearer statement. I recommend acceptance for publication in PRL if the questions raised above are adequately treated. ___________________________________________________________________