Date: Tue, 31 Jul 2001 09:11:31 -0400 (EDT) From: Physical Review Letters To: slee@fnal.gov Cc: prl@ridge.aps.org Subject: lf8481 Dr. Sungwon Lee Texas A+M Univ. MS 318 Fermi National Accelerator Lab. P.O.B. 500 Batavia, IL 60510 slee@fnal.gov Re: LF8481 Search for gluinos and squarks using like-sign dileptons in ${p}$${\bar{p}}$ collisions at $\sqrt{s}$=1.8 TeV By: T. Affolder, H. Akimoto, A. Akopian, M.G. Albrow, P. Amaral, et al. Dear Dr. Lee, 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. (X) Acceptance, if the editors can judge that all or most of the criticism has been met. (X) Return to the previous referee(s) 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 yours, Samindranath Mitra Assistant Editor Physical Review Letters Email: prl@aps.org Fax: 631-591-4141 -------------------------------------------------------------------- Report of Referee A (LF8481 Affolder,T) -------------------------------------------------------------------- This paper gives the first results on a search for like-sign dileptons in events with 2 jets and missing transverse energy from the Tevatron. Since the Tevatron is the world high energy frontier, and since this channel has especially small backgrounds from standard model processes, it is very interesting, and deserves publication in Physical Review Letters. However, before publication, I would like the authors to adress the following comments: 1) They list 4 ee, 10 emu, and 5 mu mu events passing the OS cuts. They list the backgrounds as: Drell-Yan 8.7, ttbar 4.0. other backgrounds are small. Assuming all 10 observed emu events are top and not DY, and assuming ee+mumu=emu from top, this leave no room for their Drell-Yan background? But, they list this as their dominant background? 2) I had trouble understanding the description of the SUSY model. I think the sentance "We impose common scalar and gaugino masses..." should be "We impose common scalar and common gaugino...". the first time I read this, I thought they set the scalar and gaugino masses equal at the GUT scale. Also, I'm not sure what the phrase " slepton masses which require m(squark)>=0.9m(gluino)..." means. From their description, I guessed that they took M(squark), ran it up the the GUT scale, set the slepton mass equal to the squark mass at the GUT scale, and then ran the slepton mass back down. But, then I don't understand the "require M(squark...)" bit. 3) They quote the tracking resolution, but not the electron or jet resolutions. This seems strange. I think they should quote all three. 4) Their result would be of more general interest if they tried to present their results in as model-independent way as possible. For example, they should quote the kinematic acceptance and the total lepton identification efficiency separately for several different squark/gluion masses. A theorist could calculate a kinematic acceptance for their own favorite model, and use the total lepton identification efficiency quoted as a rough guide, to translate this result into rough limits on their own model. 5) are the jet ET cuts before or after jet energy scale corrections? 6) they should update reference 11 to Phys. Rev. Lett 83 (1999) 4937 and update figure 2 to include the results in this reference. 7) this result was first presented in conference in 1996 (see fermilab-conf-96/181-E), so I'm not sure this result is really "timely". -------------------------------------------------------------------- Report of Referee B (LF8481 Affolder,T) -------------------------------------------------------------------- Using events containing like-sign di-leptons, jets and missing $E_T$ to search for gluinos and squarks in $p\overline{p}$ collisions represents a useful addition to the literature on direct experimental searches for SUSY. I judge the analysis to have been competently performed and the paper is, in general, clearly explained. This work certainly deserves to be published in PRL. I do, however, have one question concerning a feature of the data presented that looked surprising. 19 OS data events survive all cuts, a number that is consistent with the 14.1 expected from Standard Model sources. However 10 of these events are $e\mu$. The number of $e\mu$ events expected is not given. (I think it would be a good idea to give the flavour breakdown of the expected SM events.) But I would guess this number is approximately half the number expected from sources other than Drell-Yan, i.e., $2.7\pm0.5$. In making this guess I am assuming roughly equal identification probability for electrons and muons, which is obviously an approximation. On the face of it this looks like a four sigma discrepancy. Do the properties of these events (lepton $p_T$, missing $E_T$, jet activity) show any unusual features? I would suggest that some comment on the number and properties of the observed $e\mu$ events should be made in the paper. There was one particular aspect which I thought could have been more clearly explained in the paper. Some of the SUSY signal channels discussed (those involving the decay $\chi^0_2 \rightarrow \ell^+\ell^- \chi^0_1$) have to lead to events containing three leptons if they are to produce two LS leptons. Experimentally, of course, all three leptons will not necessarily be identified as isolated and high $p_T$. I think this should be mentioned in the paper. This prompts the questions (which I think should be answered in the paper): how are events with three observed isolated leptons treated in the selection and are any such events observed in the data? I had a few more minor questions/suggestions: In the sentence at the bottom of page 9: ``We define the acceptance as the ratio of the number of di-lepton events \ldots\ which contain at least two leptons.'' I assume the ``cuts'' include the requirement of LS, but the number of generated events includes both OS and LS events? Perhaps this could be spelled out. In table~I I would have been interested to see the SUSY numbers for the first two rows. Is it not possible to give, also, the SM background number for the second row? $\chi^0_2 \rightarrow \ell^\pm\ell^\mp \chi^0_1$ (middle of page~1) seems unnecessarily complicated when $\chi^0_2 \rightarrow \ell^+\ell^- \chi^0_1$ would do.