[Clascomment] OPT-IN:First comprehensive measurement of spin observables and differential cross sections dsigma/dt in omega photoproduction off the proton for 2.7 < Egamma < 5.2 GeV using CLAS

[Daniel Carman]

Dear Volker et al.,

I have read through the draft of your paper on omega photoproduction and include my comments below.
Most of my comments deal with grammar/style, but I have a few comments regarding presentation as
well. The results are quite impressive.

If you have any questions, let me know.

Regards,
Daniel
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General:
 - I prefer that there should be no space between a "%" symbol and its value. e.g. Use "58\%".
 - Throughout, use "liquid-hydrogen target".
 - You are not consistent with your use of commas in lists. Sometimes you put a comma before
   the "and" (what is called an Oxford comma - which I prefer) and sometimes you do not. Whatever
   path you choose in the paper, please be consistent with your notation.
 - You have a notation flip-flop in the paper that is not organically presented. The title and
   abstract explicitly uses photon energy notation. You then switch back and forth between photon
   energy and invariant energy W (a quantity that is not defined). Can you not choose one variable
   and stick with it throughout?
 - The presentation of your cross section figures gave rise to some comments:
   - You include the statistical uncertainties added in quadrature with the background subtraction
     method uncertainties. However, the total systematic uncertainty accounting is more than just
     the background subtraction contribution. You list other uncertainties in lines 236-246, but
     you have not explicitly stated whether these are all scale-type uncertainties or if some are
     point-to-point type (e.g. detector acceptance). I would like this clarified. Also, I think it
     makes sense to explicitly include the overall scale uncertainty factor in the figure captions
     whenever you mention the plotted error bars on your points.
   - On figures where you include data points from multiple measurements, the data points should all
     be the same size. For example, in Fig. 5, the CB-ELSA points are much bigger in size than those
     from CLAS. I think they should all be the same size. Please review in all figures.
   - On figures where you include data points from multiple measurements, you have not made it clear
     what the error bars on the different points include. You have a statement for the current
     measurement, but not for the earlier CLAS data or for the CB-ELSA data. To make this comparison
     meaningful, I also have to know what the scale-type errors are for each dataset. I do not know
     if this would help with the apparent disagreement of the CB-ELSA data or not.

Page 1:
 - Line 11. Use "The $\omega$ mesons were detected ...".
 - Line 19. Use "... mesons $\rho$, $\omega$, and $\phi$ ...".
 - Line 21. Use "... and, therefore, these ...".
 - Line 31. Use "Pomeron".
 - Line 36. Use "... observables that provide ...".
 - Line 46. Use "... photon that fluctuates ...".
 - Line 49. Use "... behavior that can be ...".
 - Line 50. The sentence ending "... QCD-inspired two-gluon exchange." needs a reference.
 - Line 52. Use "Pomeron".
 - Line 59. Typo. Use "separate".
 - Line 61. Use "... study that also ...".
 - Line 73. Use "... medium-energy regimes.".
 - Line 74. Use "In this Letter, ...".
 - Line 76. Here you give a photon energy range that differs from the title and abstract.
 - Eq.(1). Use "... \to p \omega,~{\rm with}~ \omega \to ...".

Page 2:
 - Third line from the top of the left column. Here you use a non-standard notation of $\Theta$.
   Why can't you use $\theta$?
 - Line 96. Use "statistically meaningful".
 - Line 111. Here you have "...; they are the first measurements." However, on line 107 you already
   mentioned that this is the first measurement. Drop the mention on line 111 and end the sentence
   with a period.
 - Fig. 1 x-axis label subscript is too small for readability.
 - Line 133. Use "... energy $E_\gamma$ as:"
 - Line 134. Remove "and $E_{e^-}$ is the accelerator energy" as you already defined this on line 124.
 - Line 157. Use "... sample followed ...".

Page 3:
 - Line 177. Spurious "with" on this line.
 - Line 181. Use "... subtraction technique [26], ...".
 - Line 182. Use "... which determined the ...".
 - Line 192. Use "The value of $Q$ was then ...".
 - Line 199. Use "... measurements were based on ...".
 - Line 208. Use "The Monte Carlo events ...".
 - Line 210. Use "... criteria that were applied ...".
 - Fig. 2 caption. Line 14. Remove the extra "(" in the list.
 - Fig. 2 caption. Line 17. Use "(long dash-dotted curve)".
 - Line 221. Use "... distribution, which indicates ...".

Page 4:
 - Line 238. Use "... in Refs. [20,26].".
 - Line 244. Use "... liquid-hydrogen density ...".
 - Line 252. Provide a reference to the helicity and Adair frames.

Page 5:
 - Line 282. Use "... exchanges, as well as ...".
 - Line 305. Use "... angles, as well as proton ...".
 - Line 310. Use "... and, consequently, both ...".
 - Line 329. Use "... the one for $\pi$ exchange.".

References:
 - Do not include the page range for journal references as this is not standard. Of bigger
   issue is that you are inconsistent with this usage in your bibliography.
 - Refs. [34] and [35]. Use "[CLAS Collaboration]".

Supplementary figures:
- Fig. 7 caption. Line 3. Problem with inequality notation.
- Fig. 8 caption. Line 3. Problem with inequality notation.
- Fig. 9 caption. Line 3. Use "... 4.7~GeV and SLAC [12] ...".
- Fig. 20. Line 1. Use "Adair".
- Fig. 21. Line 1. Use "Adair".