Dear Proponents, Congratulations with this nice and comprehensive analysis. Here are the comments from Nikhef. King regards, Kristof == General Questions and Comments == ==================================== General: (1) As an additional systematic check, could you compare the results obtained from a "counting experiment analysis" with those you obtain here from a "shape analysis"? That is, normalize the B and Bbar samples individually, count the number of signal events and use them to measure the direct CP violation. Section 1: Introduction Line 11-13: Although you mention CP violation in mixing as a possible source for a non-zero cosine term, you never introduce the accompanying parameter q/p, whose deviation from unity measures this directly. We therefore suggest to leave out this remark. Line 15: The penguin contributions in Bd->JpsiKs are indeed tiny, but nonetheless not negligible [especially for LHCb when it reaches uncertainties on sin(2beta) below the degree level]. Hence C is not equal to 0 in the SM, neither is S exactly equal to sin(2beta). We therefore suggest to replace the equality signs with approximation signs. Line 18-20: Is it obvious that Bd and Bdbar are in an entangled state? Line 24: This is not the first measurement at a hadronic environment, as you also admit in the conclusion (Ref. [17]). The sentence is therefore misleading. It is probably not necessary to mention this was a blinded analysis? Section 2: Data samples and selection requirements (1) In case multiple candidates in a single event survive your selection cuts you keep only the one with the smallest chi2 of the decay time fit. Does this not introduce a bias in your data sample? After all, it is possible to have an event A with two candidates whose chi2 are both smaller than that of a single candidate in an event B. If this does not introduce a bias, please explain why this is effectively a random choice. We suggest to follow the guidelines written down in the internal note LHCb-INT-2011-009 entitled "Dealing with multiple candidates". Section 3: Flavour tagging (1) Is it possible to also give the average mistag fraction and tagging efficiency (even though you don't use them) for comparison with other literature/results? (2) Could Eq.(3) be given in a more transparent notation for the reader? Like (omega - omegabar) = Delta p0, as Eq.(37) of the Analysis Note. In addition, Delta p0 should then be added to Eq.(2) as well. Section 4: Decay time acceptance and resolution (1) What about the effect of the decay time biasing requirements in the selection cuts, are they also investigated (and found to be negligible)? (2) Line 101-105 is in contradiction with section 7.2.4 of the Analysis Note. What did you finally assume for beta? Please mention its value also in the text. (3) Eq.(4) Why do you use a bias proportional to the decay time resolution estimate? This parametrization was originally motivated to describe the situation at the B factories, but seems to be unnecessarily complicated for LHCb's setup. (4) Line 114: Could you list which are the decay time biasing requirements somewhere in the text (preferably in section 2 already)? (5) We find it odd (and a little unbalanced) that you invested a lot of effort into understanding and parametrizing the resolution and hence use a very complicated per-event model, whereas acceptance effects are basically ignored and treated as systematics instead. This is even more surprising given that for the Bd system the results are not expected to be (majorly) effected by the resolution, whereas the acceptance can play a far more important role. Could you motivate why you chose this setup over a more balanced one (either simple resolution with simple acceptance, or complicated resolution with detailed parametrization of acceptance effects)? Section 5: Measurement of S and C (1) Please mention the fit range for the decay time distribution you use. Section 6: Systematic uncertainties (1) Can you motivate why comparing with an sFit is an appropriate way to extract systematic uncertainties due to background decay time modelling? (2) Your background model systematic, as extracted from difference between a standard fit procedure and the sFit procedure, seems very large. Is it possible you are overestimating this systematic? You have a very small number of background events compared to the signal, and almost nowhere in the considered mass range are you signal free. In this case we expect the sWeight procedure to be quite poor, and thus show a larger statistical dependence on these few background events. It could therefore be that the difference between the two methods is not representative for a systematic bias at all, unless the central values disagree. (3) Would using a larger mass range not help to reduce the systematic due to the background decay time modelling? == Textual Comments == ====================== General: - Please make sure that you use the same number of significant digits for all results. Thus either 1, like for S, or 2 like for C. - Could you use the same upper decay time cut in your plots, currently Fig. 1 goes up to 10.5 ps whereas Fig. 2 goes up to 12.5 ps. Preferably, this limit corresponds to the used fit range. - Please use a dash(--) to separate numbers, not a hyphen as in Lines 53, 58, 59, 62, ... Abstract: - It is not necessary to repeat S and C twice, please remove them from the first sentence. Author List: - Replace "The LHCb collaboration" with "LHCb collaboration" according to EB guidelines. Section 1: Introduction Line 5: Would "heavy and light mass eigenstates" not be a better choice of wording over "high and low mass eigenstates"? Line 21: Add "a factor": "diluted by a factor (1-2omega)" Section 2: Data samples and selection requirements Line 41-49: Mention explicitly that the event needs to be triggered by the signal, i.e. that you require the candidate to be TOS. Line 59-60: What does that sentence mean? The Ks has long decay lengths, not just non-negligible. What does "significantly measured" mean? If it means "larger than ...", indicate how large. With respect to what does it need to be significant: the PV or the B? Why do you put requirements on the decay lengths and decay time (the analysis note only mentions a cut on the decay time)? Line 64: Replace "nominal" with "known", and then there is no need to quote the PDG. Line 65: What does "clearly associated to one PV" mean? Line 66: This notation makes it look like one does a 4-prong vertex fit, which is not the case. Mention instead that you fit the whole decay chain. Line 71: This is not a well formulated sentence. Suggestion: "resolution, and candidates are required to have $\sigma_t<0.2 ps$." Line 73: Replace "Candidates are retained" with "Furthermore, candidates are only retained". Section 3: Flavour tagging Line 90: Remove the first "and". Line 93: "control channel" is not defined at this point; we assume you are referring to B+->JpsiK+? Section 4: Decay time acceptance and resolution Line 101: This is too much LHCb jargon. An acceptance is a good thing; your problem is that its shape in non-trivial. Section 5: Measurement of S and C Line 118: Replace "in a small set" with "with a small set". Line 122: The phrase "simultaneous analysis" is not clear; you split the samples but do a simultaneous fit. Line 137: Why do you capitalize "Lognormal"? Eq.5: Please be consistent in the notation of the logarithm: either "log" or "ln". Line 138: Replace "with the median M and tail k parameter" with "where M is the median and k the tail parameter.". Line 139: Replace "single lognormal functions" with "a single lognormal function". Line 142: Add "the": "PDFs of the decay" Line 152: You can shorten this sentence to "The production asymmetry has been measured by LHCb to be mu=... [15,16].". Section 6: Systematic uncertainties Line 175-176: This is not formulated in a clear way. Line 183: "nominal PDF" is not defined. Section 7: Conclusion Line 204-205: If the measurement is compatible with the B factories, it obviously is with HFAG; you can leave out one of them. References: - Most of them are incorrectly formatted; please use the LHCb template instead. In particular Refs. 1, 2 and 6 are weird. - Refs [1]: Is the Bigi book the right place? We would cite the initial paper. - Refs [2]: What is this: A thesis, An internal note?