Hoi, the comments are in. Unless I missed a really relevant point in my first quick reading, there is not much. The first referee's main point is the absence of a comparison to excl b->ulnu decays and two minor points about eff(mX) and the statistical significance of the different mX results (1.55, 1.40, 1.70). The second referee's main point is that he wants a PRD. Apart from that it's mostly a description of the difficulties reading a compressed PRL. No mention whatsoever of shape functions, Parameters, values, errors, b->s gamma, ... Cheers, --U. PS: Thorndike, that is, no Hill ... ------- start of forwarded message ------- From: Physical Review Letters <[log in to unmask]> To: [log in to unmask] Subject: Your_manuscript LG9660 Aubert Date: Thu, 11 Sep 2003 19:10:30 +0000 (UT) Re: LG9660 Measurement of the inclusive charmless semileptonic branching ratio of B mesons and determination of $|V sub {ub}|$ by B. Aubert, R. Barate, D. Boutigny, J.-M. Gaillard, et al. Dr. U. Langenegger SLAC, M/S 95 P.O. Box 20450 Stanford, CA 94309 Dear Dr. Langenegger, The above manuscript has been reviewed by our referees. We ask you to consider the enclosed comments from the reports. 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 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. Yours sincerely, Robert Garisto Senior Assistant Editor Physical Review Letters Email: [log in to unmask] Fax: 631-591-4141 http ://prl.aps.org/ ---------------------------------------------------------------------------- Report of Referee A -- LG9660/Aubert ---------------------------------------------------------------------------- This paper reports an interesting measurement of V_ub using inclusive charmless B decays. The very high statistics data sample collected by BaBar allows a much higher purity sample to be obtained, limiting the systematic errors from background that plague the earlier measurements. It is therefore very welcome, and deserves publication in PRL. The paper is generally well written, but some parts are very dense and hence unclear, lacking in necessary detail. I have a number of questions and comments, together with some suggestions for minor improvements in the text. If these can be addressed satisfactorily, I will be happy to recommend the paper for publication as soon as possible. 1) Neither the introduction or conclusion makes any reference to the other main method of measuring V_ub, namely the measurement of exclusive branching ratios B->pi l nu, B->rho l nu etc. Since the two methods are complementary and the systematics rather different, I think at least some mention of this should be made in the introduction, and the e.g. the precision achieved (including both experimental and theoretical uncertainties) compared with that from exclusive techniques in the conclusion. A reference to the most recent publications on exclusive branching ratios (e.g. the Babar paper PLB 90, 181801 (2003) and others) would be useful. 2) The inclusive method used here requires the assumption of parton-hadron duality, which is not universally accepted in this context. This is alluded to by the mechanism of reference [5] cited in the introduction, but I think this should be stated in the main text - it is an important assumption. 3) Introduction line 11: `..and by measuring the fraction of charmless semileptonic decays...' This phrase in context sounds like this technique is new, whereas it is the same as used by previous experiments. The sample purity has been improved, but the basic technique is the same, so this should be rephrased. 4) Figure 1(b): There seems to be a big dip in efficiency for m_X values just above 1 GeV - the dip in the spectrum is much more pronounced for the `all requirements' histogram than the `p*>1 GeV' histogram. What is the cause of this ? More generally, there is no comment on how the efficiency varies as a function of m_X. 5) Table 1: The first three variations (changing the m_X cut) have highly correlated data samples. Are the statistical errors on the R_u values calculated from all the data, or only the part which is independent in the two samples ? If it is all the data, the variations look a bit large to be coming from pure statistical fluctuations as is suggested in the text. E.g. for m_X<1.55 GeV the result is 2.06+-0.25, then for m_X<1.70 it is 2.35+-0.28. Taking the quadrature difference of the statistical errors as an (admittedly crude) estimate of the uncorrelated part, the difference is 0.29+-0.13. 6) Page 13 2 lines after the R_u result, the double ratio between R_u for B+ and B0 is quoted, but no discussion is given of what this result means, or why it is interesting. Is it expected to be unity ? Some interpretation would be helpful, if the result is interesting enough to derive and quote. Minor points ------------ a) Abstract line 5: 'hadronic mass distribution' is ambiguous in this context. I suggest something like 'mass of the hadronic system accompanying the lepton'. b) Page 9 line 3: 'estimated as the fraction of signal events with m_ES>5.27 GeV'. This is difficult to understand without the context of the fit shown in Figure 2 - moving the figure reference and mention of the fit earlier would help. c) Page 9, last paragraph line 3: Presumably the m^2_miss<0.5 GeV^2 requirem ent is applied before the kinematic fit setting it to zero - it would be clearer to mention that this value is calculated before the fit. d) Page 9, last two lines: The pi_s rejection is a little obscure. Is this test applied to all pions (which are then used to calculate the neutrino mass), or only those accompanied by an exclusive D0 ? The text could be clearer on the procedure which is actually followed. e) Page 10, after the equation: Several numbers are quoted with errors. What are the errors - do they include both statistical and systematic effects, or only a subset? This should be stated. f) Page 11, line 3: What is the error on the 6.8% lepton background? g) Page 11, paragraph 2 line 6: 'the first bin is extended to m_X < 1.55 GeV' This is hard to understand - extended from where ? Presumably you want to say that it covers the whole region from 0-1.55 GeV ? h) Page 12 line 3/4: plurals: '... and kaons *are* estimated... by var ying *efficiencies* by...'. ---------------------------------------------------------------------------- Report of Referee B -- LG9660/Aubert ---------------------------------------------------------------------------- This is certainly an important result pioneering a new method of measuring a crucial parameter in the Standard Model of particle interactions. All that is said in the first paragraph is correct. It deserves prompt publication. On the other hand this letter is very difficult to read leading to a great deal of confusion about what is actually done. Perhaps this results from presenting a very condensed version of a result that should be described in a longer format. This letter would be much more clear if it could reference a longer, more complete description of the analysis. Failing that the authors need to address the specific points I make below to clarify and improve the reader's ability to understand the analysis. Footnote 5) is overstated. The extraction of the c harmless semileptonic branching fraction has little to do with quark-parton duality. On the other hand the extraction of Vub depends on duality. Not enough information is given about DeltaE used in the selection of B_reco. A plot of some sort would be most useful, presumably DeltaE after a selection on m_ES comparing data and simulation, but failing that some words on the average resolution on DeltaE and the quality of the agreement between the simulation and data. It would be valuable to know what fraction of the 1097 B decay modes are actually used after the requirement on purity. I find "The purity of events with a high momentum lepton..." to be imprecise and confusing. I suggest "For B's decaying semileptonically to a high momentum electron or muon recoiling against B_reco the purity of the B_reco selection is 67% (see Figure 2a)." "Prompt" is jargon well known to those interested in semileptonic meson decays, but is otherwise confusing. It is not defined in the letter. The senten ce, "For charged..." should be rewritten to eliminate "prompt" or "prompt" should be defined on its first usage. I suggest, "For charged B_reco candidates, we require the charge of the selected lepton to be that expected from the decay of a b-quark with the proper flavor for a B meson recoiling against the candidate." The sentence, "For neutral..." has me completely confused. I think the authors are trying to say that when signal fraction and backgrounds are used later in the analysis they take into account the known rate of mixing of neutral B mesons which can result in either charge of lepton appearing in B's recoiling against B_reco. If this is what they mean then they should say it later since it is of no consequence at this point. If they mean something else then they must rewrite this sentence to make it clear. I am confused on the selection sequence for B->X_u l nu candidates. Prior to the paragraph beginning "To select..." the neutrino mass equivalent to the missing mass is fixed t o zero by the kinematic fit for m_X. Then the missing mass is required to be consistent with zero. I think the authors are trying to draw a distinction between the neutrino four vector which they require to have zero mass in the kinematic fit and thus no longer is equal to the missing mass four vector which for B->X_u l nu candidates is selected to have mass consistent with zero. They do this with the subscript nu and miss. If this is what they mean then this distinction needs to be made more clear. Perhaps the order of these should should inverted to make it clearer. Is the reported resolution on m_x for candidates that also pass the B->X_u l nu selection criteria? As written it appears to not be so in which case what is point of giving this number? The fit to the m_X distribution is done on those events passing the B->X_u l nu selection. The language describing the D*lnu partial reconstruction is unclear. Instead of "...and require for the neutrino...", it would more clear to say "...a nd eliminate if the neutrino..." At least I think that is what is done. If not then the authors need to tell us what they do with the recovered D*lnu events. Figure 1 is confusing. Is it before or after a detector simulation? It is hard to tell if any resolution in the figure agrees with what is in the text as the text gives the average resolution on m_x which is clearly much larger than what is apparent in the figure for low values of m_x. Also "Signal MC" in the caption is jargon. Better is "MC Simulation of the B->X_u l nu signal". It would be good to report the effect of the selections made going from the initial sample of B->X_u l nu candidates. Do the fractions cut away by the various selections (1 lepton, charge, D*lnu partial reconstruction, kaon veto) agree with the predictions of the simulation? If so this would strengthen the belief that the background is well modeled. Does the shape of m_ES distribution for the B_reco signal agree with the prediction of the simulation? Again if so it would strengthen belief that simulation is a good model of the data. Table I and the description of the fit to Figure 3a is very confusing. First when N_sl is first mentioned in the text, Table I is not referenced. Thus I was left trying to figure out if the N_sl in the table was the same as the one in the text. I think it is, but reference to the table in the text when the fit to m_ES to extract N_sl is explained is necessary to clarify. Second the first three rows of the table leads one to believe that the fit is only performed on the subsample that passes the indicated m_X cut. Careful reading of the text indicates that this is not the case, but rather the cut only defines, I think, the size of the first bin in which N_u and N_c are reported. This is confusing as the table leads one to believe that the first three fits are performed on different subsamples and even after reading the text many times I am not sure that m_X < y means what I think it does. The meaning of m_X in the table needs to be made clear. The entire description of the fit could be made more clear by adding some guidance as to how the fit to the m_X distribution works. N_c is essentially determined by the data in the m_X bins above 2.0, and is extrapolated into the low region by the shape of the m_X for this background as predicted by the simulation. Saying this explicitly would aid understanding the discussion of the systematics. It would very much aid understanding if the m_X distribution for the control sample is shown comparing data and simulation. At least characterize in words the agreement between data and simulation for high values of m_X. At the moment the authors are asking to accept on faith that they have a good understanding of the m_X distribution of the B->clnu background. How is the 1% error for track finding efficiency applied? Is it 1% per track or is 1% the overall effect of the uncertainty? It is not clear that the identification efficiency errors are reasonable. The author s need to give some evidence that the variations is ID efficiencies and mis-ID rates given in the paper are reasonable. No error seems to appear for the choice of m_X. Why not? While the variation in R_u shown for the choice of m_X in Table I is probably an over estimate of the error, the Table shows a trend, the highest R_u for the lowest m_X and the lowest for the highest, that seems to indicate that the choice of m_X and the fit value of R_u are correlated. At least the authors should comment on the trend and explain why the choice of m_X does not contribute to the systematic uncertainty. There is no comparison with other, exclusive measurements of V_ub. One PRL 90, 181801 (2003) is even by the authors collaboration. Besides comparisons with other inclusive measurements something should be said about the exclusive measurements. ------- end of forwarded message -------