Dear all,

Here are my comments to the D->mumupi paper.

General comments:

How was the binning chosen? The fact that you see leakage from the resonances into your central bin seems to defeat the point of binning. Couldn't you rebin in a more appropriate way. More generally, if you do a search without any apriori knowledge, why do you bin at all? Cannot you publish a background-subtracted dimuon spectrum or Dalitz plane?

The usual question about multiple candidates : Can you prove that your choice of best candidate does not bias the result. i.e. are BDT and vertex chi2 uncorrelated? See LHCb-INT-2011-009.

Line 99: is there any kinematic requirement that aligns the momentum distribution of D->3pi to D->pimumu? The muon-ID strongly biases momenta. That affects your statement in line 132 that the shape is "well defined"

Writing: I find it could be improved a lot. Line 7: remove the spaces inu mu- mu+. Line 9: why "see Fig 1" here? The figure doesn't illustrate the sentence. Line 12: best -> most stringent (?) Line 15: "Throughout... implied": why this sentence here? Line 23: "subject of great interest at LHCb". That may be true but is of no interest to the outside world. What about a sentence saying LHCb is very competitive in RD charm? Line 25: add a comma at end of line. Line 26: samples -> bins. Remove the 2nd for. Line 47: The L0 _trigger_ Line 48: I have nothing a priori against ">" in text, but here some of the operators could easily be replaced by words, like > 1.68 -> exceeds. Why the parenthesis around GeV/c? You could write "exceeds (1.3 GeV/c)^2". Line 49: have _a_ momentum ... and _an_ impact Line 52: "be," -> is Line 55-56: The last sentence is obvious. Remove. Line 60: $\chi^2_{NDF}$ -> $\chi^2/{\rm NDF}$. $\chi^2<30$ of what? Is that a chi^2 or a chi^2/dof? Line 62, 75, 78: Please do not use Loki functors in publications. You could replace DIRA by some angle (e.g. $\theta_d$) or just repeat the definition in line 75. ("and known as the DIRA" would be "known as DIRA" anyway). Line 69: so -> and thus (?) Line 72: the BDT trains -> the BDT is trained Line 78: MAXDOCA is undefined. Line 80: "The variable" ... and then the equation Line 93: are forbidden -> must not Line 98: rewrite as "... except for the requirement that two of the tracks have hits in the muon system." Line 106: as the -> in the (?) Line 108: in the m(...) -> in m(...) Line 113: know -> known Line 129: Please say how the tails are fixed. MC? Line 142: _the_ large width. Rewrite as "The statistical significance of the two observed peaks are 6.1 and 6.2 for D->eta(pi) and Ds->eta(pi), respectively." (assuming that's what it means). Line 147: As no ... windows upper limits. Line 165: "a number" what number? Line 196: "imperfect emulation". The online reconstruction is not emulated but re-run. What do you mean? Table 3: Effect -> Systematic error

Cheers,

Patrick