[Clascomment] OPT-IN: Cross sections for the exclusive photon electroproduction on the proton and Generalized Parton Distributions

[Michel Garçon]

The lead authors would like to implement these changes:

- We should be more cautious on the statement in the abstract (last sentence) on "nearly model-independent...". We omitted here to say "leading-twist", which is a key word. As soon as higher-twist (and higher order)are considered, the extraction is no longer "nearly model-independent". We will replace "nearly model-independent" by "leading-twist", and leave the qualification of the extraction for the text, not the abstract. (see below comment on l. 271). Besides, the model-independence refers to the GPD (or CFF) themselves, not to the framework within which the amplitudes are calculated.

- l. 34-35: "in terms of four-vectors in an obvious way" is not so well said. What about "in terms of the electron and proton four-vectors" ?

- l 271: it really is here leading-twist and leading-order for DVCS (order refers to the pQCD expansion in alpha_S, twist refers to the QCD/OPE expansion in 1/Q). We propose: "At leading-twist and leading-order, this procedure uses well established DVCS amplitudes and does not depend on model parameterizations of the GPDs. We fit simultaneously...."

- l 309-310: b is indeed linked to the transverse size of the nucleon, but is not directly the transverse size (there are kinematic-dependent proportionality factors). It could be confusing if somebody tries to quantify the transverse radius as 1/sqrt(b). We would replace "interpreted as" by "linked to" or another expression to the same effect. Or "related to" might be better. The exact mathematical expression would lead us too far.

- Remove ref [40], which is useless as is.

-	+ miscellaneous syntax changes.