[Clascomment] OPT-IN: First measurement of direct photoproduction of the a2(1320) meson on the proton

[Daniel Carman]

Dear Andrea et al.,

I have read through the draft of your paper on a2 photoproduction from g12. A
very nice piece of work that was a pleasure to read. Most of my comments deal with
grammar/style. If you have any questions, let me know.

Regards,
Daniel
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General:
 - You are not consistent through with handling speed of light units c. I suggest you choose a
   presentation format with c=1.
 - You alternatively shift the order of pion-eta and eta-pion in listing the final state. Please
   be consistent.
 - For your figure caption, use "(Color online)". However, I don't think PRL requires this
   disclaimer any more.

Page 1:
 - Line 38. Use "... dynamics give rise to ...".
 - Line 44. Use "So far, only a few ...".
 - Line 47. Use "... collected by the GRAAL ...".
 - Line 52. Use "Understanding $\eta \pi$ production ...".
 - Line 54. Use "non-resonant".
 - Line 59. Use "... allowing for the interpretation of the variations ...".
 - Line 60. Use "... as a signature for the existence of exotic resonances.".
 - Line 78. Use "... analysis, all three hadrons ...".

Page 2:
 - Line 97. Use "beamline".
 - Line 108. Use "vs.".
 - Line 141. Keep units with their values using, e.g., "100~MeV".
 - Line 161. Use "The final state photon CVM elements, ...".
 - Line 168. Use "... the four photon invariant mass ...".
 
Page 3:
 - Fig. 2 caption. Line 3. Use "... with the smallest ...".
 - Line 194. Use "vs.".
 - Line 201. Use "... after ordering the photons, the ...".
 - Line 203. Use "... corresponding to the $\eta$, with some ...".
 - Line 209. Use "... variables that can be split ...".
 - Line 210. Use "... allows reconstruction from each event source ...".
 - Line 215. Use "... to assign to each event a ...".
 - Line 219. Use "... as control variables.".
 - Line 227. Use "... resulting in a bias ...".
 - Line 237. Use "... code that included knowledge ...".

Page 4:
 - Table I. Wrong units on t width.
 - Table II.
    - Capitalize "Systematic Uncertainty Source".
    - Four first four sources listed, remove the extra space between the value and the
      "%" symbol.
 - Line 256. Use "... the photon ordering ...".
 - Line 257. Use "... and the sPlot method."
 - Line 264. Use "... equal to the square root ...".
 - Line 281. Use "... cross section was obtained ...".
 - Line 299. Use "exponentially suppressed". (No hyphen if first word is an adverb.)
 - Line 302. Use "This ranged from a few MeV ...".
 - Line 324. Use "... shows the statistical ...".
 - Line 326. Use "The colored bands at the bottom show ...".
 - Line 328. Use "... uncertainty for $d^\sigma ...".

Page 5:
 - Line 350. Use "... trajectories only, which for the production ...".
 - Line 357. Use "... implies the parameters of the Regge ...".
 - Line 387. Use "... GeV$^2$, which can be ...".

Page 6:
 - Fig. 4 caption. Last line. Use "... respectively for a beam energy of 4~GeV ...".
 - Line 402. Use "... Council (STFC), ...". Remove "under grant numbers".

References:
 - [6]. Drop "1405.4286".
 - [15]. Use "B.A. Mecking".
 - [17]. Use "M.D. Mestayer".
 - [18]. Use "E.S. Smith".
 - [20]. Use "Y.G. Sharabian".
 - For CLAS-Note references, [21], [22], [23], give URL to file location.
 - [27] is out of order. Should go after [28].