Subject: Your_manuscript DU8917 Toback From: Physical Review D Date: Mon, 30 Aug 2004 16:40:04 +0000 (UT) To: wagnp@fnal.gov Dear Dr. Wagner: The manuscript ``Prospects of searches for neutral, long-lived particles which decay to photons using timing at CDF'' (DU8917) by David Toback and Peter Wagner has been reviewed by one of our referees. Comments from the report are enclosed. These comments suggest that the present manuscript is not suitable for publication in the Physical Review. Sincerely, D. Nordstrom Editor Physical Review D ------------------------------------------------------------------------------ Report of the Referee ------------------------------------------------------------------------------ I have found it very difficult refereeing this paper. The general subject matter is interesting to me anyway and so I found the paper very intriguing. However, particularly since the paper falls within the proposed experiment category and contains only prospects based on simulation and a feasibility study, I believe that the paper does not reach the standards expected of an article in the proposed experiments category. I therefore recommend that the paper not be published in your journal. I have included below (after the main comments for reference) the section regarding Editorial Policies which you pointed out to me. There are also a number of issues related to the method which would have to be clarified before I would endorse the paper as definitely scientifically sound. Normally, in the refereeing procedure, the scientifically sound issues would be those which I would expect would possibly be addressed satisfactorily in response to the referee's comments. There are quite a few of these issues: but it is difficult to gauge how heavily to weigh these in my deliberations since the standards of scientific-soundness appropriate to a "proposed experiment" paper (eg. feasibility) necessarily differ from an actual experimental result (correctness). My conclusion is that the "proposed experiment" is probably feasible - largely because timing resolution of 1 ns is achieved. A related issue is that the content of the paper is very focussed on the improvements possible from using timing. It does not really get into much detail regarding the overall feasibility of the measurements. In this sense I would classify the content of the paper as rather narrow. In addition, to this basic content issue, the paper is currently rather verbose and in my opinion, presented at a quite pedestrian level. There are also several typos etc which I would have expected should have been caught prior to submission with proper internal review. Last, but not least, I am concerned that other collaborators particularly those who have done much of the work related to the CDF EMTiming upgrade have not been included as co-authors. Ref 2 indicates that there are about 15 people directly involved in this upgrade project. I will now address the first two issues in more detail. Proposed Experiment Issues -------------------------- The paper discusses prospects for using the IMPROVED timing measurement capabilities of the upgraded CDF detector for photons. This is an upgrade which is taking place, and apparently is in excellent shape - reasonably close to completion. There appears to me to be no impediment at all to the authors and their collaborators reporting and publishing actual physics results of such studies based on data, either data already collected, or in a year or two. I judge the "proposed experiment" to probably be FEASIBLE, although the definitive information which mostly leads me to this is information from a presentation by Goncharov available at the URL in reference 2 indicating the timing resolution for electrons. It would be preferable if such information was directly in the paper - and presumably Goncharov and others who contributed more to building and commissioning the detector should then be authors. Also by largely limiting the paper content to the prospects for the photon-timing to improve the search reach, the authors have not really addressed in much detail, the actual feasibility of the search as a whole, relying largely on old publications with a different detector operating in different accelerator conditions. More details related to this are contained in my "scientifically-sound ?" comments. I don't think the "proposed experiment" is particularly NOVEL. The authors are not proposing a whole new experiment. They are simply documenting that a particular technique shows particular prospects for significantly improving the sensitivity for some particular types of new physics. Their collaborators on EMTiming also recognize that timing the EM calorimeter signals adds to the physics reach of the experiment - this is an upgrade which is funded and installed. So the main issue in terms of being novel is : Is doing a toy MC simulation of a particular hypothetical process, which MAY lead to resolvably delayed photons, something that is novel and worthy of publication in Phys. Rev. D ? My judgement is that it is NOT; it is a straightforward calculation based simply on kinematics. Using timing for photons is not something that is new, it was already used by CDF (although not as well using the HADCAL), and has been used by other collaborations in the past and documented in their publications based on data. The one thing that is a bit novel, is proposing to use the timing information to positively identify late photons, but the time-of-flight technique is not in itself novel. Regarding "authors' responsibility to show that their proposal is likely to stimulate research that might not otherwise be undertaken". It would appear to me that the main audience that needs to hear about this research is the CDF collaboration as they are the only ones able to carry out this proposed physics analysis in THIS MANNER. Perhaps there might be an argument that other experiments eg the LHC experiments might learn from it - although much of the discussion is very CDF specific, and I suspect the LHC bunch structure and intrinsic calorimeter timing resolution make it hard to apply. I also note that eg. the Chen and Gunion paper (1997) already addresses much of the material here in a much more general, albeit more phenomenological, way. Anyway - the authors haven't demonstrated that this would stimulate research that might not otherwise be undertaken outside of the CDF collaboration. I would also say that the paper falls very much within the GENERALLY UNSUITABLE category in terms of using straightforward calculations based on well-known models and describing simulations of apparatus and a feasibility study. Comments on the Paper itself (mostly regarding the scientifically sound question) ---------------------------- o Extrapolating from published papers by a factor of 20 in luminosity with a different detector without really any recent data studies to back it up looks precarious. a) There seems to be some disconnect between eg. TABLE III and reference 10. Ref. 10 has an acceptance cut of ET > 55 GeV not 25 GeV as stated in text. If the cut was 25 GeV, I'd expect much more Z gamma SM background. Ref 10. says 12 events in 87 pb-1, this says 12.6 in 100pb-1. b) with the different bunch structures from runI to runII and different expected integrated live-times of the EM_Calorimeter, I'd expect that one should not extrapolate cosmics based on integrated luminosity. The conclusion might be that cosmics are much less of an issue if 2 fb-1 is really going to be delivered fairly quickly. The paper has no discussions on detector gating issues - indicating lack of attention to experimental detail relevant to this type of search. o several assumptions in the introduction indicate that the depth at which this study convincingly demonstrates that the measurement is definitely feasible is a bit lacking. I would have expected that the authors would have done more to evaluate the effect on the acceptance and photon-ID from the photons not pointing. This is particularly relevant to the "low boost" part where the timing separation is significant. o These two comments suggest to me that the authors have not really yet done much of the groundwork needed to carry out such a measurement should they have the data on tape. o the paper suggests that only m_gravitino < 1 keV is cosmologically interesting AND theoretically favored. This does not seem to be justified at all in reference 14, which I note was not refereed. Chen and Gunion (in ref. 5) note that m_gravitino should be < FEW keV in "most cosmological scenarios [6,7]". They chose < 2.5 keV. CG References [6,7] suggest to me that the < 1 keV number sometimes quoted in the literature comes from an early paper which did not consider possible additional effects in the cosmology. In particular, CG ref 7, suggests to me that 100 keV is a priori more interesting based on known sparticle mass limits and suggests ways in which the cosmology could have dilution mechanisms (of gravitino mass density). o My general impression of these GMSB studies is that there is no really solid theoretical guidance on what is "theoretically favored". I think it is fair to say that this paper indicates that the sensitivity of the CDF experiment can be extended in lifetime by about a factor of 1.5 with this EMtiming technique (over pointing alone in CDF). Having 2 techniques is very good for any potential discovery. However I think it is misleading to give the impression that with this analysis all the theoretically favored and cosmologically allowed parameter space would be covered. It is my understanding that lifetimes of order 104 - 108 s are even under consideration in related models. o LHC. You may want to consider discussing whether or not such sensitivity is also possible at the LHC. o contradictory figures. some figures have 110 GeV but captions have 70 GeV. If the intent is really to demonstrate complementarity to LEP it would be more representative if all such figures were for 110 GeV. o many "<" and ">" are mistyped or funny font. o In a paper which contrasts both existing limits based on data (ALEPH) with prospective limits estimated from simulation IF 2 fb-1 is collected, care should be taken in comparing the two types of information. A legitimate question might be: Is there any region where a 5-sigma signal could be robustly observed with 1 fb-1 which is not already excluded ? It is not really feasible for the reader to evaluate this since no comparisons of signal and background event counts are given. o The LEPII exclusion is actually just from the ALEPH experiment - and it should say so. Where appropriate it would be reasonable to also refer to other results from LEP experiments. o In particular, I suspect there are more stringent limits from LEP available at least in the form of preliminary results. o I suspect the ALEPH results are more general. Does the GMSB model used really allow comparison of the Tevatron prospects and LEP data ? It would seem to me that the Tevatron cross-sections depend sensitively on the gluino and squark masses, while for the LEP analyses the actual parameters that matter are indeed the neutralino mass and lifetime. Again, the plot needs to make it clear that these are not really apple with apple comparisons. o The reference by D0 authors in [12] indicates impact parameter resolution of about 1.5 cm for D0. The photon pointing Appendix which indicates that timing is a better tool for CDF than pointing should point out that the plots are just for CDF and that D0 should have much better sensitivity using pointing. o particularly sections II and III are fairly verbose with a lot of material which was not presented in a very insightful way. For example, why present "perfect measurement" cases for efficiency estimates. Surely only those including resolution are relevant ? o Appendix A formula should have a factor of 7/9 in the argument of the exponent. o Fig 18. "doubles" -> "halves" ? O p23. "result" -> "prospective result" (again distinction between a result and a prospect) Editorial Policies excerpt : "Papers that describe proposed experiments fall into a special category. For such papers to be acceptable, the experiments must be demonstrated to be novel and feasible. It is the authors' responsibility to show that their proposal is likely to stimulate research that might not otherwise be undertaken. Generally not suitable for Phys. Rev. are papers proposing a new experiment using straightforward calculations based on well-known theories or models, and papers describing simulations of apparatus or optimization or feasibility studies." ------------------------------------------------------------------------------