From dmacqueen@physics.utoronto.ca Fri Jan 5 16:19:24 2001 Date: Wed, 25 Oct 2000 12:43:33 -0400 From: Dan MacQueen To: reb@anl.gov, johny@fnal.gov, velev@fnal.gov, rlc@fnal.gov, frisch@uchep.uchicago.edu Cc: cdf_toronto@physics.utoronto.ca Subject: Comments on "Searches for New Physics in Events with a Photon and b-quark Jet at CDF" Dear Authors and Godparents, Some members of the Toronto group have read the first draft of the "Searches for New Physics in Events with a Photon and b-quark Jet at CDF" PRD. We have prepared a list of general and specific comments on your paper. We're sorry for the delay in getting these comments to you. We hope you find these useful. Thank you again for all your hard work, Dan MacQueen, for the CDF Toronto group. ========================================================================== General comments: ----------------- It is not clear what the motivation for this paper is. Instead of investigating the relevance of a specific model, you start from a very general signature (b + high Et photon) and add several requirements to set limit on various supersymmetric models. It follows that your additional cuts (for instance at the end of section 2) are unmotivated, which can be very confusing for the reader. Instead of starting from such a general stance, it might be useful to relate the additional cuts to more specific models in the introductory chapter, so that the reader has an idea of what you are looking for (given that this paper is a PRD, adding a couple of paragraphs to relate the phenomenology of the models to the experimental requirements should not be a problem). It seems that, like the e-e-gamma-MET paper, we are trying to turn a few events into the justification for a complete study. It is not clear this is enough. We see many parallels between the approach taken here and that espoused by our colleagues from Frascati in their "discovery of the s-bottom". One important difference here is that we have not discovered a signal of any significance, so we are concerned with setting limits. As in that case many parts of this paper might be more appropriately authored by a smaller subset of individuals rather than the whole CDF collaboration. We feel that much of the discussion in sec 4 surrounds events that we end up dismissing, thus diluting the main discussion of events which are "more significant". The appendix attempts to quantify a difficult subject. It is not clear to us that there is much scope for generalised acceptance*efficiency calculations. In cases where the method proposed by the authors works it should be possible for clever theorists to know what parts of phase space a model excludes "safely". In the interesting cases (where on 30% exclusion can be achieved in the simplified approach) it is not clear that concluding this without the benefit of a full simulation is risky. Should the CDF collaboration really be endorsing this? Specific Comments: ------------------ Abstract: 1) It would be a good idea to put some numerical results in the abstract. Section 1: Introduction 1) "Major responsibility" sounds awkward, and seems to place the wrong emphasis on things -- perhaps refer to the search for new physics as a "major opportunity"? 2) The first sentence in the second paragraph should be divided in two ["...heavy particles which can decay into constituents (quarks, bosons, etc.) Due to the large mass..."] 3) "transveese" -> "transverse". 4) "a disproportionally large branching ratios" should be "disproportionally large branching ratios." 5) The statement that "these hypothetical particles have disproportionally large branching ratios" is too strong -- this is only true in some models, although those are the models you look at. 6) Throughout the paper, you alternate between E_T and E_t for transverse energy. It would be better to standardize this to E_t. As well, you should put the symbol for missing transverse energy in italics, rather than putting a slash through a Roman E_t. 7) You should explain, expand, or define CDF, MSSM, and GMSB, rather than just putting the acronyms in without explanation. Section 2: Data Selection 1) Section 2.2: "Bremstrahlung" -> "bremsstrahlung". 2) In the final sentence of section 2.2, you state that the requirement that the vertex be less than 60 cm from the centre of the detector is made so the "projective nature of the calorimeters is preserved." This is actually done to ensure the detector contains the entire jet. 3) In section 2.3, paragraph one, you state that you require the EM cluster be isolated to remove backgrounds from jets and electrons. In fact, photons can't be found near jets (that is they may be there, but we can't look there.) You should rephrase this to explain what this does for the efficiency. 4) Section 2.3, third paragraph -- "to be less" -> "be less". 5) Section 2.4: B-tagging is a 2-pass algorithm, where the first pass looks for two tracks, while the second pass looks for more than two tracks. You have combined the two passes into one sentence here. 6) Section 2.5: "...one signature is not obviously more likely than any other" seems like editorializing. 7) Section 2.5, second paragraph, first sentence: Missing E_t has already been defined, so this sentence isn't needed. 8) Why did you choose Delta Phi (photon - missing E_t) < 168 degrees, rather than some other value? As well, this optional requirement is included in the background, but the other optional requirements are not. 9) It should be made clear that your H_t is different from the H_t used in other analyses. Section 3: Background Estimates 1) Is table 2 really necessary? it doesn't provide any additional information and can be confusing. Column 2 is labelled "calculation", when it really is "method" and the content of the second column is not clear to whoever hasn't read the whole chapter (for instance, why using CES+CPR as a way to find the mistag+real photons background?). 2) section 3.1: The sentence "are significantly diluted in their discrimination power" is not very clear. Why not just say that the discrimination power is low at high energy? 3) section 3.3: the last paragraph could be removed. 4) Where does this 20% additional uncertainty for unmeasured effects come from? (explain in a sentence or give a reference). 5) section 3.5: this section is redundant with section 3.1 (apart from the actual number of photon background). Wouldn't it be better to merge the 2. I don't understand how you evaluate the fake photon background at high Et (in section 4, you claim it is an approximation made by applying the fake photon measurement and the positive tagging prediction to the large statistics untagged sample": is it some sort of extrapolation from the low Et sample?). 6) In section 3.3, you claim that you expect different "mistag" background values in the QCD sample and in the photon+missing Et sample. Can you measure or quantify in some way the difference? Then you wouldn't have to quote a 50% uncertainty on the mistag background (section 3.6). 7) section 3.7: "bremstrahlung" -> "bremsstrahlung". Section 4: Data Observations 1) Table 3: The significant digits are not good here: it should be 0 +/- 5 rather than 0.3 +/- 5, 0.0 +/- 0.1 +/- 0.1 instead of 0 +/- 0.1 +/- 0.1, etc. 2) In Figure 1a, it is difficult to tell the dashed background prediction from the dotted SUSY model prediction. 3) In Figures 2b & 2d, you label the y-axis Events/2.1 -- 2.1 what? Also, is the Delta phi between the missing E_t and the nearest jet referred to in the text at all? 4) In tables 4, 5, and 9, we don't think that the run and event numbers need to be recorded. 5) We're unclear on the motivation behind section 4.2 -- why do you discuss four events which don't pass the cuts if the backgrounds are not established for them? 6) In table 8, significant digits are not expressed properly -- 0 +/- 2 +/- 0.4 should be 0.0 +/- 2.0 +/- 0.4, etc. 7) Last sentence of second paragraph should read "... we note nothing else..." 8) In figure 6, you should mention in the caption that the solid dots represent the data. Text inside the figure should also be removed, as that information is in the caption anyway. Section 5: Limits on Models of Supersymmetry 1) p22. You include a lot of terms that are not defined (or poorly defined) in the introduction of this section. Examples include: "model limits", "signature-based limits", "gauge-mediated concept", "SUGRA". 2) p22, 2nd paragraph of sec. 5.1: Have you every really defined the MSSM spectrum of particles in this paper? We looked back at the introduction and didn't find it there. Couldn't a few sentences be added to draw the parallels between the SUSY charginos and the SM charged bosons? 3) p22, 3rd paragraph of sec 5.1: By the same token you don't define M_1, M_2, beta, mu. Maybe only particle physicists will get this deep into the paper, but even for some of them only beta will be an "everyday term". 4) p23, 1st full paragraph: Which is the cause and which is the effect. You seem to imply that region 2 merits the most attention because Pythia models it reliably. Is this because they chose to code it up first because there is something more reliable about the physics? That would be a stronger argument to use. Basing our choices on what phenomenologists have put in their models seems like poor motivation. 5) p23, 2nd full paragraph, 2nd sentence: "To decide where in the region to place..." seems to missing a verb. Maybe if you read "=" as "is equal to" then you get a complete sentence. But this is not very good English. 6) p24, line 7&8: "The charginoS and neutralinoS parameters..." You don't need the "S"s here. 7) p24, line 11: It took us a long time to figure out what the physical significance of the top-stop threshold was. Another sentence explaining how they are neutralino produced (should it be top-anti-stop?) might make this a little easier for people who don't deal with this physics every day. 8) p24, end of 4th full paragraph: Doesn't the fact that you couldn't come up with a set of parameters that doesn't predict a Higgs boson that should have already been found at LEP make the "nominal point" of the model much less interesting? 9) p24, 4th paragraph: Haven't we published cc-MET search that Regina and Andrei were doing a few years ago? Even in a conference proceeding? 10) p25, 2nd full paragraph: Haven't we settled on a 4% luminosity uncertainty for all of run I now that the top cross-section has been published? Section 6: Model-Independent Limits: 1) In the first paragraph, mention that the script L is integrated luminosity. Section 7: Conclusions 1) The concluding sentence should say what you mean by "with a reliability of approximately 30%" -- does this mean a 30% uncertainty? References: These need a careful grooming for punctuation. Separate papers in the same reference should be separated by semi-colons and end with a period. It looks like you know this but have mixed and matched references from other places as some end with periods in the middle and others have a semi-colon at the very end. See for example: 1, 2, 9, 11 and 17. 1) "et al." should follow the first author and have a comma after it. cf.19 and 20. 2) When you quote a second paper by the same authors you should include the authors name again. cf. 1 and 11. 3) Ref 3 should not have the paper title included. 4) Nucl. Instrum. and Methods Phys. Res., Sect. A should be used consistently (cf. 4 (ok), 5 (nice), 7 (could use work), 24 (missing the "A") and 25 ...) 5) Couldn't ref 15 just be a footnote, or better yet included in the text? 6) You should use serial commas consistently in lists of 3 or more authors. We think ref 22 is the only place you use a "," in front of the "and" as in `xxx, yyy, and zzzz'. 7) Ref 30 is in appropriate if Weiming is an author on this paper, does it really differ from 31. Guess so, but still. 8) Ref 32 is not very satisfying. There are no proceedings available from this workshop (yet?). Maybe a reference to the webpage for the meeting would be better than just the statement that a workshop was held -- which is almost clear from the text in the paper body.