[Clascomment] OPT-IN:Longitudinal target-spin asymmetries for deeply virtual Compton scattering

[Michel Garçon]

Hi Silvia et al.,

Thanks for your detailed answers to my first comments.

- As I told you before, there are some approximations in BMK (Dieter acknowledged this some years ago). Unfortunately, their new and more complete paper BMJ is not so clear. And no, I am not sure that DVCS2 appear in sin(phi) at leading order. Some terms are not clearly defined. So I take this back for now. This being said, we know more now than in the early papers. Especially if you do not mention "leading twist" in those sentences, I would keep my comment: instead of "which are a signature of the interference...", something like "which are expected to arise mostly from the interference..". This is not asking you to soften a statement compared to what we said years ago, but to acknowledge (implicitly) that we know more details now on the formalism. Again, if you do not mention leading twist, DVCS2 contributes to the asymmetry (sin2phi at least for sure).

- On the definition of CFFs, I wait to see the next version of the paper, but I would insist it would make more sense for our collaboration to have a consistent convention in all its DVCS papers. With all due respect to the authors of ref [8],of whom 2 are distinguished CLAS collaborators, the definition of CFFs as 4 imaginary quantities, is a more widely accepted one (among others eq. 17 in arXiv:1101.2482 - with same author that introduced the other convention previously - , eq. 4 in 9905372, eq. 9 in your ref. 6, etc...) and one that makes more sense. 

- Importance of H_tilde: you have not shown that H_tilde dominates the TSA. I continue to think (and it was for example in ref.13) that the H and H_tilde contributions are of the same order of magnitude (I will not argue here on the exact value of the ratio, I was just giving back of the envelope estimates). The only way you can see that is by turning off and on each contribution in VGG for example. So I agree of course that TSA is sensitive to H_tilde, but any statement that (implicitly) leads to believe it is uniquely sensitive to H_tilde is misleading. It is the case on line 265 where it is said that BSA and TSA are mostly sensitive to H and H_tilde respectively. The truth is, BSA is mostly sensitive to H, and TSA gets its main contributions from both H and H_tilde, thus adding a sensitivity to H_tilde. Thank you for the CFF plots, but they do not disprove the above. You have to look at the relative contributions to substantiate any statement (+ the relative errors on ImH 
 and ImH_tilde from Michel's fit are not so different).

Looking forward to the next version.
Michel Garçon.