Hi All,

I have received comments from Wouter and Tjeerd (thanks!) and have integrated their comments with mine.

Unless someone objects or has additional comments this is what I propose to post around 23:00 this evening.

Cheers, Hella

____________________

Dear authors,

Congratulations with the very nice analysis and results. Please find below the comments from the Nikhef group.

regards, Hella

Abstract: 1 fb^{-1} -> 1.0 fb^{-1}

The paper:

L3: Specify "quarkonia" as "heavy" or even better "charmed". This paper and the "available models" concern only those specific mesons. Replace "can either ... b hadrons" by "can be produced directly, or indirectly via decay of higher excited states (feed down) or via B meson decays". ("either" applies here to three possibilities. Without the "," in "directly, from cascade decays" it would only apply to the last two. Be consequent with writing "feed down".)

L7-8: Replace "of the cross-section and the polarisation" by "of the production cross-section and of the polarization of promptly produced charmonium states". Otherwise it is not clear to what "the polarization" applies.

L23: Replace "Measurements of the chi_c production and the relative amounts of chi_c1 and chi_c2 spin states have previously been made using different particle beams and energies [8-12]" by "Measurements of chi_c1 and chi_c2 production cross sections for various colliding particles and energies have been reported in"

L29: Write "radiative J/psi decay".

L30: which -> that

L31: Replace "The converted photons are reconstructed using e+ and e- tracks" by "The photons that convert between the vertex detector and the first tracker station before the magnet are reconstructed by the e+ and e- tracks through the magnet".

L33: Replace "of converted photons is better than that of calorimetric ones (i.e. non-converted or converted after the dipole such that ... single cluster in the calorimeter)" by "of these "converted" photons is better than that of photons detected as a single cluster in the calorimeter ("calorimetric" photons) without the momentum information of e+ and e- particles".

L37: Replace "These two measurements are highly uncorrelated, in particular the uncertainty due to the photon reconstruction as it is based ... reported here" by "The systematic uncertainty due to the photon reconstruction in Ref.[12] is based on calorimetric information and is very different from the present one which is based on track information".

L42: 'has never been observed at hadron colliders' -> 'has never been observed before at hadron colliders'

L83: - Replace "bremsstrahlung radiation" by "bremsstrahlung". - Replace "the conversions are reconstructed only with tracks ..., ensuring that the photon converts between the downstream end of the VELO and the first tracking station" by "only converted photons are reconstructed with tracks ... to ensure that the photon converts between the VELO and the next tracking station".

L90: You use 'y' and later (L. 98) also 'z' but the coordinate system is not defined. We suggest to define this when you describe the LHCb experiment in Sect. 2.

L90: - Replace "photons" by "a photon". L91: - Replace "linear extrapolation" by "straight line extrapolation". - Replace "electron track" by "electron (positron) track".

L92: - Replace "are selected and their momentum" by "is selected and its energy". - Replace "electron momentum" by "electron (positron) energy from the reconstructed track."

L110 and further: We do not understand why you need the cut on 40mm. Since the 2nd vertex will very often be within 40mm it is hard to understand why this rejects more background than data. The PV resolution is 30 micron, so all you are testing here is how well downstream twoprongs can be matched to a PV, which is almost random. Why isn't it enough to require that the converted photon and the J/psi forma good vertex?

We are also really puzzled by the valued of your chi2 cuts, which are order 100 per dof. We cannot put those values in the paper, because it can only mean that we try to do something with very poorly calibrated errors. So, please replace with something much vaguer like "We require the jpsi and photon to form a good vertex and that the chi_c candidates points back to a primary vertex."

Did you try and understand why you need such a very large chi2 cut to be efficient for signal? It cannot be the j/psi vertex or its IPchi2, because those we understand reasonably well. How are the errors on the parameters of the converted photon determined?

L115: lower -> smaller

L126: 'of a photon' -> 'for a photon'. This sentence is confusing. Is the total chance of a photon converting before the first tracking station 20%? Please clarify the text.

L140: Here and in the rest of the paper J/Psi (and other particles) should be followed by nouns like 'meson', 'hadron' or 'candidate'.

L149 and further: The part about the combinatorial background description is very difficult to follow. Why do you use a factor two, is there a specific reason for that? Suggestion for L151 and further: "It is therefore important to reproduce well their angular distribution in order to obtain the correct shape for the invariant mass." -> "In order to correctly reproduce the angular distribution, to obtain the correct invariant mass shape, fake photons are constructed from the selected converted photons in the sample. For each... "

L152: add comma between task and fake

L230-231: The 3% sounds arbitrary due to the formulation that you use. If you describe the 'other bins' you might want to write. 'The other bins show no significant bias within the 3% uncertainty of the test. A systematic uncertainty of 3% is assigned to all bins.'

L281 Section 7: This is a strange section. You describe the chi_{c0} analysis fully, including systematics, efficiency and results in the middle of an ongoing paper. We suggest to either integrate the parts in the rest of the document or move this after the chi_c1/chi_c2 results.

L352-353: "This is the first chi_c0 observation at hadron colliders." -> "This is the first observation of chi_c0 mesons at hadron colliders."