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

[Sebastian Kuhn]

Nice paper. Just a couple comments:

Fig. 4): There is a lot of information in these figures, and it might be possible to make it easier accessible and clearer with a few changes. For one, it's not clear that one really needs 3 different t values in each row - by choosing only two, the plots can be made bigger which would be a big improvement. Also, the caption should contain at least a list of the curves/shades drawn - it would become a little longer that way but would make the figure much more understandable (instead of having to hunt in the text for the explanations). Ideally, the figure would fill (most of) one column, but I understand you are pressed for space (is PRL still THAT restrictive? I thought I recently saw some indication that they allow a little more space now...)

In the discussion of that figure, you state "Figure 4 shows that the predictions of standard GPD models like VGG, GK, and KM10a, whose compatibility is remarkable in spite of their different approaches, are in good agreement with our unpolarized cross-section data." Also, in the abstract it says "Several models of Generalized Parton Distributions (GPDs) describe the data well", as well as in line 324-7 (flip the order of "the data" and "well" in that sentence). One could argue that the difference between Chi2/dof = 1.9 and 1.5 is very significant, so maybe it would be fair to say KM10a does the best job. This is even more obvious once you include the polarized data. In fact, as Fig. 5 also shows, VGG does not describe the data at low x very well.