I share Tim's point that there should be a brief paragraph explaining the uncertainty in the value of the nucleon-nucleon cms system, and why LHCb quotes the energy as "5 TeV"

We are not sure this is necessary in the note, provided that we say that this is the nominal value. It may suggest that the issue is relevant for the results presented in the note. However, if you feel like adding a sentence on why in your papers you use 5 TeV as sqrt(s), we are not against

Burkhard already prepared a small paragraph that we could add to the note. Given the fact that different values for the center-of mass energy are are quoted in different publications, it's worth pointing out why, even if it does not affect the physics we are talking about.

In the caption of Table 1 I think that it should be made clear that the values provided in the Table cannot be taken directly from the referenced publications, by adding the word 'rescaled to the rapidity range [2.5<y<4]' somewhere. It would also be useful to provide the rescaling factor and to explain how the original uncertainties are treated (e.g. no rescaling in the case of LHCb).

We suppose that for you these are integrals of your differential values rather than rescaled values.... For us this is the full range so the issue should not be there.

For LHCb the values indeed have been extracted from published numbers, and that should be said. The rescaling for the 2.76 TeV data actually requires a bit more explanation, but those details should be described elsewhere, i.e. in the LHCb analysis note or a shorter separate document.

For LHCb there should be a new reference to the updated j/psi cross-section at 7 TeV included in the paper on the J/Psi polarization at 7 TeV (arXiv:1307.6379), as I understand that this is the input that was used for the interpolation.

This seems correct to us.


In the caption of Table 2, the word 'relative' is confusing, as pointed out by Ralf already. My understanding is that the cross-sections in Table 2 are absolute cross-sections in mub. Then, for the sake of comparison they are normalized such that sigma(sqrt(s)=5.02). The parameters p0 and p1 are determined by fixing the interpolating functions to the theory value at 2.76 and 7 TeV; finally with these values of the parameters one looks at the shifts with respect to the reference value of 5.3 mub. I hope that I understand things right! At any rate I think that the text should be made a bit more user friendly here!

See our suggestion to the equivalent Ralf's question. We probably need to be a bit more reader-friendly here.

one could consider to normalize all predictions in table 2 to the same value at 5 TeV.

Also, I tried to reproduce the FONLL result using Cacciari's web-based tool, but did not manage... What is exactly the (nominal) FONLL cross-section? How is it defined?

The kinematical region 2.5<y<4, 0<pT<8 GeV/c was used. Pdf is CTEQ6L. Uncertainties are those related to both scales and quark masses. So this last point should be mentioned in the caption of table 2 (now it isn't).

A priori one would think that the systematic uncertainties on the cross-section measurements at 2.76, 7, and 8 are extremely correlated, given that it's the same detector, same machine instruments, the same method to measure the luminosity... For fully correlated errors the combined precision cannot be better than the best point. If this is not the case, it should be explained.

This is indeed something that requires some more discussions/thinking. A good point for our next meeting, probably.

according to the LHCb lumi group the uncertainties on the luminosity are (somewhat surprisingly) only very weakly correlated. It turned out, that for different periods als different effects dominated the systematics.

-- EnricoScomparin - 14 Nov 2013

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