[Clascomment] OPT-IN:First observation of correlations between spin and transverse momenta in back-to-back dihadron production at CLAS12

[Daniel Carman]

Dear Harut et al.,

I have read through the draft of your CLAS12 paper on correlations in dihadron production
that is intended for publication in the Phys. Rev. Lett. I do not have substantive comments
on the physics as I really do not have great understanding, but I have some comments on
the Introduction. I also pass along my comments on grammar/style. If you have any questions,
let me know. Good luck with the reviews and submission process.

Regards,
Daniel
---------------------------------------------------------------------------
General:
 - You are not consistent with your use of hyphens throughout the manuscript. Better to leave them
   all out and led the PRL editors handle it than to handle things in a haphazard manner.
   
Page 1:
 - Line 12. Use "The data were taken with electron beams of energy 10.2 and 10.6~GeV incident on ...".
 - Line 14. Use "CLAS12 spectrometer".
 - Line 79. Use "... polarized electron beam ...".

Page 2:
 - The text after line 88 (unnumbered lines before Eq. 1) through line 110 are absolutely impenetrable
   for me. PRL is supposed to be for a general audience. I cannot imagine this formalism is understood
   by more than a handful of folks in the world. I recommend that you spend some time to make this
   formalism more approachable with more complete references woven into the text. Without understand
   this part, the results cannot be (fully) appreciated.
 - Line after line 88. Use "... see Fig. 1 ..."
 - Line 114. Use "... spring 2019 using 10.6 and 10.2 GeV longitudinally polarized electron beams ...".

Page 3:
 - Line 140. Use "The reconstructed electrons and hadrons were required ...".
 - Line 142. Use "... a formal cut was placed on ...". By the way, what is a "formal" cut? Why is this
   word even needed?
 - Line 172. Add a comma after "$P_{beam}$".
 - Line 190. Here and on the next page, you refer to an appendix. No appendix was included with the
   paper. Seems to me that as this is to be submitted with the paper, that it should be included for
   the Collaboration to review.
 - Line 195. Problem with the subscript on the momenta. Should be "T1" and "T2" to be compatible with
   earlier usage.
 - Line 199. Use "... shown in Fig. 4, has ...".

Page 4:
 - Fig. 3 and Fig. 4. Why do these figures have different y-axis labels? If this was done on purpose,
   one distribution unweighted and the other weighted, you need to explain why this was done. As given
   in the paper, it seems like a random choice.
 - Line 205 and line 209. Use "Fig." not "FIG."
 - Line 205. "The dependence appears relatively weak and may be a consequence of u-quark dominance ...".
   This needs some development or appropriate references. Why do you make this claim? Is it pure
   speculation on your part?
 - Line 210. "... in terms of correlations with other variables such as ...". I am not sure what to make
   of this statement. You need to develop your discussion with some explanations for the reader.

Page 5:
 - Line 253. Here you introduce and discuss your largest source of systematic uncertainty, but never give
   a precise scale for the effect. It should be mentioned here.

Refs:
 - Put your references in the order cited in the paper.
 - Be consistent with how you list collaboration names. I prefer "(CLAS Collaboration)", "(HERMES Collaboration)",
   etc.
 - You should not list arXiv information for already published papers.