Comments on b-hadron lifetimes paper
Dear all,
Here are the comments I collected during the Bfys Meeting on Friday 4 March. Please, correct and improve the text below.
Best regards, Tjeerd -----------------------------------
Dear authors,
We like to compliment you with this well written paper. Our comments are grouped in (i) suggestions for the text, (ii) comments on the content, and (iii) questions on principles.
Suggestions for the text: ======================== Abstract: Replace "tau^single" by "tau^eff"
In http://arxiv.org/pdf/1011.1096v1 Eq.(24) and (25) this quantity is described as the "effective lifetime". What the effect of the limited proper time range is in the fit, we do not know. The suffix "single" is not clearly standing for "single exponent fit". Maybe "fit" may warn against a physics interpretation if "eff" is not correct.
line 2: Change to "Reconstructed exclusive b->JpsiPhi decays ..."
The first word of this paper "Exclusively" is used wrongly, as it is meant to specify "exclusive decays" and not "exclusive reconstructions". The rest of the sentence "... the pursuit of several important measurements at LHCb" is less clear than would be, for instance, "... the measurement of b-hadron lifetimes that are important for the physics we explore in LHCb."
line 6: Change the last subscript L into H.
Caption 1: Change to "PDG evaluations of ...", and change "lifetimes" to "mean lives"
"World" average is a nice understatement for a presentation, but not descriptive enough for a paper. In the quoted reference: tau_B+,B0,Lambdab are called "mean life" and its value "our evaluation", tau_B0s is called "mean life" and its value "our evaluation for 2/(Gamma_B0s,L + Gamma_B0s,H)". I would be good to give also the name "B0s decay rate average Gamma_s" with the definition of Gamma_s.
line 22: Remove "approximately"
It is not clear why this number varies between 35 and 38. The addition "approximately" suggests that we really do not know, how much was analysed. Addition of "proton-proton collisions" to "at a centre-of-mass .." would be more precise.
line 46: Replace by "Mean life determinations"
"Extracting" in a title is not correct. The lifetime is the duration that a particle has lived until decay, and is different for each produced b-hadron. Common are the average life-times, or also called mean life by the PDG, for B+, B0, etc. It would be good to change "lifetime" to "mean life" or "average lifetime" throughout the paper.
Comments on the content: ======================= section 2: We propose to add a table with cuts and add a short description, including pT cuts and clone decays. Or refer to a paper where this cuts are discussed.
We realize that this may be a major change.
line 44: Remove this sentence or rewrite it.
It is not clear what the "V0 decay length significance" is. And also the "additional requirement" is not specified.
line 54: Remove the sentence "A generous systematic uncertainty is assigned ..."
Systematic uncertainties are discussed in section 5. The sentence suggests that a problem is swept under the carpet, it contains the word "generous", and it unspecific by mentioning "potential differences".
line 62: Add the explanations of the long and short components, combinatorics and two or more tracks, respectively (as described in the analysis note according to DvE).
line 73: "... is not perfect". Mention what the consequence is. For example, "this is included in the systematic error due to the time resolution model."
line 95: The zero lifetime modeling needs more discussion. Also no error is assigned to possible contribution of misalignments to the proper time dependence of the time resolution. Maybe the effect is small, but it should be mentioned with the other sources in Table 3.
line 111: Remove "the context of", or remove the whole sentence "understanding of ...".
It seems that not much understanding has been achieved in view of the large systematic error for the proper time acceptance. The proper time resolution model also needs more discussion. Should this sentence be a warning against our CP violation analysis? What is the meaning of this sentence here?
Questions on principles: ======================= line 78: The proper time cut of 0.3 ps could have been changed in 0.5 ps. And the difference could have been discussed.
section 4: Why are no ratio of mean lives given? They may suffer less from systematic uncertainties.