[Clascomment] OPT-IN: First CLAS12 measurement of DVCS beam-spin asymmetries in the extended valence region

[Daniel Carman]

Dear Maxime et al.,

Congratulations on completing your DVCS analysis of the new RG-A CLAS12 data and preparing
a very nice paper. I have read through your paper draft and pass along my comments below. If
you have any questions, let me know. Best of luck with the submission and review process at
the journal.

Regards,
Daniel
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General:
 - You referenced supplementary material that will be submitted along with the paper. That
   material also needs to be carefully reviewed as part of the CLAS Collaboration review
   process. Please provide me with a link to the document so that I can read it for comment.
 - At several places in the manuscript you write with a present verb tense. It is proper
   style to use past tense. I point this out in my comments listed below.
   
Page 1:
 - Author list:
   - Line 4. Use "(CLAS Collaboration)".
 - Abstract:
   - Line 7. Use "... the first measurement of the DVCS beam-spin ...". 
   - Line 9. Use "Bjorken-$x$". 
   - Line 10. Use "... new data points ...". 
 - Line 16. Use "... including the composition of ...".
 - Line 17. Use "... distributions [1-5].".
 - Fig. 1.
   - This figure is low resolution/fuzzy. It should be replaced. Also, the outgoing photon leg
     is not labeled.
 - Line 28. Use "(see Fig. 1)".
 - Line 33. Use "... complex functions that are ...".
 - Line 40. Use "As BH and DVCS share the same ...".
 - Line 43. Use "... processes and the cross section can ...".
 - Line 55. Use "... to the GPD $H$ [6,7].".
 - Line 69. Use "... polarization was $\sim$86\%.".
 - Line 86. Use "Hadrons are identified using ...".

Page 2:
 - Analysis question. Line 99.
   - I am confused about how you handle events with multiple photons > 2 GeV. What fraction of events
     have N_gamma > 2 GeV? How are these events handled in your analysis?
 - Line 101. Use "... 2~GeV were considered as ...".
 - Line 103. Use "Exclusivity was ensured by ...".
 - Line 115. Use "... states is cut as".
 - Line 116. Use "$M^2_{e'p'\gamma}$". Note that this form should be used consistently throughout,
   including in the Fig. 2 label.
 - Line 117. Use "$ep \to e'\gamma X$".
 - Line 124. Use "... photon, the target photon emits ...".
 - Fig. 2.
   - The label font size needs to be increased.
   - You have introduced a new x-axis label $\theta_{cone}$. Use the notation, $\theta_{\gamma\gamma}$
     that you already defined.
 - Fig. 2 caption:
  - Line 1. Use "... and cone angle $\theta_{\gamma\gamma}$".
  - Line 3. Use "... the full dataset showing the $\pi^0$ ...".
 - Line 138. Use "... we applied the technique developed in Ref.[15].".
 - Line 140. Use "... -sample was created from ...".
 - Line 142. Use "$M^2_{e'\gamma\gamma X}$".
 - Line 145. Use "... contamination was derived by ...".
 - Line 147. Use "... the decays that lead to DVCS ...".
 - Line 149. Use "... decays was optimized between the desired ...".
 - Line 154. Use "... squared mass for the determined ...".
 - Analysis question. Line 158.
   - I find your discussion about the pi0 background treatment confusing. Back on line 100, you
     stated that your histograms are filled using all events with at least one high energy photon.
     This seems to allow for unwanted pi0 contamination. In the past, in my understanding, DVCS
     analyses from CLAS required events with one (and only one) photon. Then the pi0 contamination
     comes about from events where one pi0 decay photon is detected and one is missed. This is
     accounted for using a relatively straightforward geometric acceptance correction.
   - Your discussion starting at line 158 just is not so clear to me.
 - Line 158. Use "... contamination was determined ...".
 - Line 159. Use "... thus disentangling the ...".
 - Line 161. Use "... which was done on a bin-by-bin basis.".
 - Line 162. Use "... method determined the ...".
 - Line 167. Use "... for each bin by:".
 - Line 172. Use "... asymmetry with reasonably accuracy, $A^\pi$ was set to 0 for ...".

Page 3:
 - Line 175. Use "... between the DVCS and $\pi^0$ cross sections, ...".
 - Line 177. Use "... uncertainty was added quadratically ...".
 - Line 182. Use "(see Fig. 1).".
 - Line 184. Use "... process) were computed using ...".
 - Line 188. Use "... -bin was further subdivided ...".
 - Line 188. Normally folks use t - tmin.
 - Line 191. Use "... statistics, was implemented ...".
 - Line 198. Use "... kinematic values were computed ...".
 - Fig. 3. Increase font size.
 - Line 206. Use "Thus, the average kinematics ...".
 - Line 216. Use "... generator that included ...".
 - Line 217. Use "... calculations of Ref.[29].".
 - Line 222. Use "... with a beam energy of ...".
 - Line 224. Use "dataset".
 - Line 228. Use "The first study was based on a GPD-hybrid model [30], with sea ...".
 - Line 231. Use "... techniques were applied ...".
 - Line 232. Use "... of the model were fitted against ...".
 - Line 236. Use "dataset".
 - Line 242. Use "... PARTONS Collaboration ...".
 - Line 243. Use "datasets".
 - Line 244. Use "... to the quoted systematic uncertainties, thus yielding a ...".
 - Line 254. Use "... how closely it agrees ...".
 - Line 255. Use "$k$-replica".
 - Line 262. Use "minimally biased". (No hyphens with adverbs.)
 - Line 264. You have inconsistent usage of "reweight" vs. "re-weight". Check the manuscript
   for consistency.
 - Line 266. Use "... -bins that had similar ...".
 - Line 267. Use "In Fig. 4, it can be ...".
 - Line 271. Use "dataset".
 - Line 273. Use "... and real parts of the CFFs through ...".
 - Line 275. Use "$N_{eff}$".

Page 4:
 - Fig. 4. Use finer binning on he y-axis with finer tick marks for easier reading.
 - Fig. 4 caption:
   - Line 4. Use "... in the tables in the supplemental material.".
 - Line 278. Use "$N_{eff}$ was found ...".
 - Line 279. Use "data points".
 - Line 281. Use "... ANN that are in agreement with the JLab 6-GeV data ...".
 - Line 286. Use "dataset".
 - Line 288. Use "... space that could only be ...".
 - Line 291. Use "... (VGG) [35,36] ...".
 - Line 317. Use "high-precision".
 - Line 321. Use "... associated to this Letter".

Page 5:
 - Fig. 5 caption:
   - Line 1. Use "... compared with the KM15, ...".
   - Line 2. Use "... are available in the tables in the supplementary material for the full
     dataset.".

References:
 - Your style in the references is not consistent. Some journal names you abbreviate and
   some you fully write out. Also, for a published paper, you should not include the
   arXiv number as well. Finally, for several papers you give the article title.
 - Ref. [12], [13]. Use "(COMPASS Collaboration)".
 - Ref. [20]. Use "S. Stepanyan {\it et al.} ..". Do not list 3 authors before the et al.
 - Ref. [27]. This is a CLAS Collaboration paper. Include the collaboration name.
 - Ref. [30]. This is the only reference with the author names listed in a different style.