[Clascomment] OPT-IN: Measurement of the beam spin asymmetry of ep -> e'p'eta in the deep-inelastic regime with CLAS

[Daniel Carman]

Dear Bo et al.,

I have read through your draft of the eta DVMP paper and include my comments
below. The paper is well laid out and the presentation seems clear to me. Most of
what I have provided below will serve to improve the grammar and readability of
the paper. If you have any questions, let me know.

Regards,
Daniel
---------------------------------------------------------------------------
Page 1:
 - Abstract:
   - Line 1. Use "$ep \to e'p'\eta$.
   - Line 5. Use "... amplitudes of the $\sin \phi$ ...".
   - Line 7. I suggest to remove "(LT')" from the abstract as it is not explained here
       and seems a bit too much detail to include here. I think that "longitudinal-transverse
       interference" is sufficient here.
   - Line 10. Use "... and provide new constraints ...".
 - Line 19. Use "... to study nucleon structure ...".
 - Line 35. Use "... GPDs that involve ...".
 - Line 42. Use "... polarized photons.".
 - Line 53. Use "... underestimating the measured ...".
 - Fig. 1 caption:
   - Line 2. Use "The symbol $g$ represents the gluon that is exchanged between the quark
       lines.".
 - Line 74. Use "... produces a large number of ...".
 - Line 75. Use "... observables that are sensitive ...".

Page 2:
 - Line 78. Use "Under the GPD formalism, the ...".
 - Line 81. Use "The treatment of the electroproduction of $\pi^0$  and $\eta$ mesons
     within the ...".
 - Line 84. Use "... and $F^d$ are the up and down ...".
 - Line 105. Use "$\sigma_{LT'}$".
 - Line 107. Use "... photon polarizations, where ...".
 - Line 109. Use "... virtual photons, and $\sigma_L$ and $\sigma_T$ are the unpolarized ...".
 - Line 111. Use "... to the ratios of the unpolarized ...".
 - Line 112. As you gave the definition of alpha, so too give the complete definitions of the beta
     and gamma terms.
 - Line 116. Use "... GPD convolutions, respectively.".
 - Line 117. Use "Therefore, any sizable ...".
 - Line 120. Use "... the measurements by the CLAS Collaboration of large single ...".
 - Line 123. Use "... and of the unpolarized structure ...".
 - Line 126. Use "... in the pseudoscalar channels, and a strong sensitivity to ...".
 - Line 132. Use "Hall B".
 - Line 134. Use "... polarized electron beam and a 2.5~cm long liquid hydrogen target.".
 - Line 137. Use "... from M{\o}ller electrons, focusing them towards the beam line, while allowing ...".
 - Line 144. Use "... measuring the 2$\gamma$ decay channel.".
 - Line 146. Use "... and matching it in time with signals ...".
 - Line 149. Use "... effectively suppressed the background ...".
 - Line 161. Use " Use "Additionally, a geometric cut was ...".
 - Line 164. Use "... of the four final state particles, the following ...".
 - Line 166. Use "$ep \to e'p'\eta".
 - Line 169. Use "These cuts rejected ...".
 - Line 170. Use "... $\rho$, and $\omega$ production, ...".

Page 3:
 - Line 183. Use "$M_x^2(e'p')$" twice on this line.
 - Line 184. Use "... of the $e'p'$ system in $ep \to e'p'X$;".
 - Line 185. Use "$M_x^2(e'\gamma\gamma)$" twice on this line.
 - Line 186. Use "... of the $e'\gamma\gamma$ system ...".
 - Line 187. Use "$ep \to e'\gamma\gamma X$".
 - Line 191. Use "... topologies, respectively, ...".
 - Line 193. Use "($ep \to e'p'X$)".
 - Line 201. Use "... different meson production channels.".
 - Line 202. Use "... for the IC-IC topology in a representative $\phi$ bin.".
 - Line 203. Use "... the application of the other exclusivity cuts, the ...".
 - Line 206. Use "... suggests that the background ...".
 - Line 208. Use "... linear function and, therefore, can be ...".
 - Line 210. Use "$M_{\gamma \gamma}$".
 - Fig. 2 caption:
   - Line 1. Use "($e'p'$)".
   - Line 2. Use "... before applying the exclusivity cuts ...".
   - Line 3. Use "... and after applying the $3\sigma$ cuts on $M_x^2(e'\gamma\gamma)$ ...".
 - Fig. 3 caption:
   - Line 1. Use "... in a representative $\phi$ bin ...".
   - Line 2. Use "... of the IC-IC configuration, ...".
   - Line 3. Use " ... (dotted line). The solid line is the sum of both contributions.".
 - Line 214. Use "... that the selected events ...".
 - Line 215. Use "... inelastic regime, cuts on the invariant mass ...".
 - Line 222. Use "... the four momentum transfer ...".
 - Line 232. "The first-order bin centering corrections ...". What does this mean?
 
Page 4:
 - Fig. 4 caption:
   - Line 3. Use "... dimensional bins {$Q^2,x_B$} ...".
 - Line 247. Use "... applied to the parameters ...".
 - Line 250. Use "... and $\gamma$ in the denominator were ...".
 - Line 258. Use "... with the statistical uncertainties.".
 - Line 261. Use "The extraction of the beam spin ...".
 - Line 262. Use "$ep \to e'p'\eta$".
 - Line 263. Use "The main source are the event selection procedures, ...".
 - Line 268. Use "... used to assign the systematic uncertainties, which were evaluated ...".
 - Line 271. Use "... lead to a systematic uncertainty of ...".
 - Line 274. Use "... global normalization uncertainty ...".
 - Line 274. The systematic uncertainty on the Moller measurement of the beam polarization is
    significantly underestimated here. The standard number is 3-4% and is due to the combined
    uncertainty of the polarization of the Permendur foil and the assumed analyzing power.
 - Line 276. Use "... 8.2\%. The systematic uncertainties are shown as the grey shaded ...".
 - Line 278. Use "... in Figs. 4 and 5.".
 - Line 280. Here you use parentheses to list the bin where you had been using curly brackets.
 - Line 288. Use "... the dependence of the underlying ...".
 - Line 291. Use "... and $\tilde{E}$, thus allowing us to separate the real ...".
 - Line 292. Use "... parts of the transversity GPDs.".
 - Line 293. Use "... suggest that the interference ...".
 - Line 298. Use "... GPD-based models by Goloskokov-Kroll (GK) [20] and Goldstein-Gonzalez-Luiti
     (GGL) [22]."
 - Line 299. Use "Both models calculate ...".
 - Line 301. Use "... GPDs with their $-t$ dependence incorporated from Regge ...".
 - Line 303. Use "... difference between these models is their GPD ...".
 - Fig. 5. You are missing units on Q2 in your figure keys.
 - Fig. 5 caption:
   - Line 3. Here you use parentheses to list the bin where you had been using curly brackets.
   - Line 4. Use "... represent the systematic uncertainties ...".

Page 5:
 - Line 308. Use "... the fact that very few ...".
 - Line 312. Use "In the GK model, chiral-odd ...".
 - Line 315. The acronym PDF is not yet defined.
 - Line 315. Use "... $\bar{E}_T$, while the contributions from ...".
 - Line 319. Use "The GGL model predicts a large ...".
 - Line 325. Use "... formalism, $\sigma_{LT'}$ ...".
 - Line 330. Use For $\eta$ production, ...".
 - Line 335. Typo on "behavior".
 - Line 338. Use "... between the GPDs ...".
 - Line 340. Use "... do not have a flat behavior in $-t$, but their product produces a flat slope
     for both the $\pi^0$ and $\eta$ channels.".
 - Line 343. Use "... flavor combinations, the difference ... between the $\pi^0$ and ...".
 - Line 344. Use "... may provide insight into ...".
 - Line 350. Use "... DVMP, will ...".
 - Line 351. Use "... in the GPDs.".
 - Line 356. Use "... in all kinematic bins.".
 - Line 362. Use "... the GPD formalism ...".
 - Line 365. Use "Comparison with the GK and GGL model calculations indeed shows the ...".
 - Line 367. Use "... of the GPD parameterization, ...".
 - Line 373. Use "... existing GPD models and ...".
 - Line 374. Use "... future GPD quark ...".
 - Line 377. Use "Physics Divisions".
 - Line 368. Use "... (STFC). Jefferson Science ...".

References:
 - [3]. Typo on M{\"u}ller.
 - [26]. Include "CLAS Collaboration".
 - [30]. The CLAS NIM paper is not a CLAS Collaboration paper.