[Clascomment] OPT-IN: Beam-Spin Asymmetry in semi-inclusive electro-production of a hadron pair

[Daniel Carman]

Dear Marco et al.,

I have read through the draft of your paper on di-hadron beam spin asymmetries. I am
not an expert in this area of physics but I did my best to do a careful reading of
the paper. My comments are given below. If you have any questions, let me know.

Regards,
Daniel

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General:
 - Use "electroproduction" not "electro-production" throughout.
 - Use "beam spin asymmetry" throughout, no hyphens, no capitalization.
 - You are not consistent with usage of "twist-3" and "twist-three". I prefer the
   former.
 - You are not consistent with usage of "1D" vs. "one dimensional" and "2D" vs.
   two dimensional".
 - You should always write the asymmetry as $A_{LU}^{\sin \phi_R}$. Sometimes you
   write it as $A_{LU}^{sin \phi_R}$. Please fix this throughout.

Page 1:
 - Author listings: Use "Enrico Fermi" - you have mismatched quotation mark types.
 - Abstract.
   - Line 12. Use "... collected in Hall~B at ... beam on a liquid-hydrogen ...".
   - Line 13. Use "... pion pair with the CLAS detector.".
   - Line 14. Use "... for the kinematic variables of ...".
 - Line 28. Use "... to study QCD dynamics, ...".
 - Line 35. Use "fixed-target facilities".
 - Line 41. Use "... in this letter - six parton distribution functions (PDFs) ...".
 - Line 42. Use "... up to the twist-three level.".
 - Line 54. Use "In addition, it encodes information ...".
 - Line 55. Use "... the quark mass, as well as genuine ...".
 - Line 56. Use "... quark-gluon correlations [2].".
 - Line 78. Use "... of the cross sections corresponding ...".

Page 2:
 - Line 83. Use "... $e_q$, with $M$ the target mass and $m_{\pi^+\pi^-}$ the
     invariant mass ...".
 - Eq.(5). End with a comma, not with a period.
 - Line 92. Use "... virtual photon, and will be important ...".
 - Line 97. Use "... of the beam and target, ...".
 - Line 104. Use "... the final state hadrons in the pair ...".
 - Line 108. Use "... twist-3 contributions, as well as the ...".
 - Line 113. Use "... $F_{UU}^{\cos \phi_R}$, which is considered in the ...".
 - Line 116. Use "... leading-twist function and a twist-3 one, which could ...".
 - Line 124. Use "... first-order terms.".
 - Line 132. Use "... beam on a 5-cm ...".
 - Line 133. Use "The CEBAF Large Acceptance Spectrometer ...".
 - Line 135. Use "... oppositely charged pions ...".
 - Line 138. Use "... photon is required to be ...".
 - Line 142. Use "... current-fragmentation region were selected ...".
 - Line 151. Use "... at the few percent level by ...".
 - Line 156. Use "... average beam polarization over ...".
 - Line 170. Use "... \phi_h - \phi_R$, and performing ...".

Page 3:
 - Line 171. Use "cross section".
 - Line 200. Use "... for $m_{\pi^+ \pi^-}$, where ...".
 - Line 203. Use "... is 1.77~GeV$&^2$.".
 - Fig. 2 caption:
   - Line 3. Use "gray".
   - Line 4. Use "statistical".
 - Fig. 3 caption:
   - Line 3. Use "gray".
 - Line 215. Use "gray".
 - Line 217. Use "... corresponds to the asymmetry ...".
 - Line 218. Use "... [27], while the ...".
 - Line 219. Use "... band corresponds to the ...".
 - Line 224. You change notation here. You have been using x and now for the first and only
    time you have x_B. Be consistent.

Page 4:
 - Fig. 4 caption:
   - Line 4. Use "gray".
   - Line 4. Use "... band corresponds to ...".
 - Line 237. Use "... sources of uncertainty that were shown ...".
 - Line 241. Use "... luminosity, which will ...".
 - Line 251. ... to the transverse momentum ...".
 - Line 252. Use "... di-hadron measurements establish the basis for ...".

References:
 - Put the references in the order in which they are cited in the paper.

Supplementary Material:
 - Line 387. Use "The full kinematic ranges ...".
 - Line 388. Use "... and systematic uncertainties are provided ..."
 - General: Include units (where appropriate) in all column headings.
 - Table 1 caption. Use "... the respective projections."
 - Table 3 caption. Use "Asymmetries ...".
 - Table 5. Formatting problem in 3rd column.
 - Table 5 caption. Use "Asymmetries ...".
 - Table 7 caption. Use "Asymmetries ...".
 - Table 9 caption. Use "Asymmetries ...".