OPT-IN:Measurements of Beam Spin Asymmetries of π± π0 dihadrons at CLAS12

[Daniel Carman]

Gregory,

I have read through your paper draft on the beam spin asymmetry in di-pion SIDIS and pass along my 
comments below. I have a general comment and a list of specific comments for your consideration. Let 
me know if you have any questions. Good luck along your path forward.

Regards,
Daniel

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General:
 - You are planning to submit this manuscript to PRL. I am concerned that the current form of your 
   paper (especially the Introduction) is too specialized and too jargon-filled to have a high 
   probability of acceptance. I recommend that you take a step back and broaden your viewpoint to that
   of non-specialist in this di-hadron physics. Aim whenever possible to reduce/eliminate the jargon,
   explain all variables (not just give a definition), and try to put things in a broader context.
   Be brave and ask the input of someone at Duke not involved in nuclear physics (that is your target 
   audience!).
   
Page 1:
 - Abstract.
   - Line 3. Use "... electron beam off an unpolarized proton target, ...".
   - Line 4. Use "... Boosted Tree (GBT) ...".
   - Line 7. Use "non-zero".
 - Paragraph 1. Line 3. Use "(collectively called partons)".
 - Paragraphs 2 and 3 are a bit too specialized. Here, in the Introduction, it is especially important
   to have a broad viewpoint with minimal jargon.
 - Paragraph 2. Line 5. Use "... (QCD) functionals, can ...".
 - Paragraph 2. Line 7. Use "higher-twist".
 - Paragraph 3. Line 2. Use "higher-twist".
 - Paragraph 3. Line 6. Use "... $h_L(x)$, and $e(x)$, ...".
 - Paragraph 3. Line 10. Use "... and $h_L(x)$, which have ...".
 - Paragraph 3. Line 11. Introduce the notion of "Wandzura-Wilchek-type approximation.
 - Paragraph 4. Line 4. Introduce the notion of the nucleon $\sigma$ term.
 - Paragraph 5. Line 4. Use "leading-twist".
 - Paragraph 5. Line 6. Use "... of a quark $q$ to form ...".

Page 2:
 - Paragraph 3. Line 8. Use "non-zero".
 - Paragraph 4. Line 3. "spring" should be lowercase (not a proper noun).
 - Paragraph 4. Line 8. Use "... using the Forward Detector of CLAS12, ...".
 - Paragraph 4. Line 11. You have detailed all of the Forward Detector elements except for the
   Forward Time-of-Flight (FTOF). Without precise timing, the Event Builder cannot work. Also,
   you have said nothing about the CLAS12 Central Detector. If it is not part of your analysis,
   you should say so here.
 - Paragraph 5. Line 1. Use "... events were selected ...".
 - Paragraph 5. Line 4. Use "... effects were minimized ...".
 - Paragraph 5. Line 6. Use "... cut was placed ...".
 - Paragraph 5. Line 8. Use "... $\pi^0$s were built ...".
 - Paragraph 5. Line 12. Use "... [20]. The CLAS12 ECals are prone to reconstruction inaccuracies when
   stray ...".
 - Paragraph 5. Line 19. Use "... cut was applied ...".
 - Paragraph 5. Line 23. Use "... 0.6~GeV cut seen in ...".
 - Paragraph 6. Line 2. Use "... or $x$-Feynman, ...".
 - Paragraph 6. Line 6. Use "... we applied a cut ...".

Page 3:
 - Line 1 after Eq.(3). Do not indent this line.
 - Eq.(4). End with a period. The next line should use "Here ${\mathbf q}$ ...".
 - Fig. 2 caption. Line 6. Use "... spanned between the two planes.".
 - Line 2 after Eq.(7). Use "... DiFF $\tilde{G}^\sphericalangle$, which spectator ...".
 - Line 5 after Eq.(7). Use "... fragmentation function, but also ...".
 - Two lines before Eq.(8). Use "... GeV/$c^2$, we extend ...".
 - Line 2 after Eq.(8. Use "... sinusoidal modulation and ...".
 - Last paragraph. Line 4. Use "Systematic uncertainties in ...".

Page 4:
 - Fig. 3 caption. Line 1. Use "... (middle row), ...".
 - Fig. 3 caption. Line 2. Use "... $P_{h \perp}$, and ...".
 - Fig. 3 caption. Line 3. Use "The shaded bands associated with each data point represent the corresponding
   systematic uncertainty.".
 - Paragraph 1. Line 10. Use "... the scale uncertainty on the beam polarization(assigned to be 3\%).".
 - Paragraph 1. Line 13. Use "... asymmetries, where on average, ...".
 - Paragraph 1. Line 21. Drop the last sentence as it is out of place. The information should be included
   on line 10 (as noted above).
 - Paragraph 2. Line 3. Use "... of the fit background purity function ...".
 - Paragraph 4. Line 6. Use "non-zero".
 - Paragraph 5. Line 1. Use "e.g." (not "ex").
 - Paragraph 5. Line 3. Use "... are visible in the $A_{LU}^{\sin(\phi_h - \phi_{R\perp})}$ measurement
   of both channels as a function of $M_h$.".

Page 5:
 - Paragraph 3. Line 11. Use "... to isolate this elusive ...".
 - Paragraph 3. Line 13. Use "... and offering an ...".
 - Paragraph 3. Line 15. Use "Beam spin asymmetries near ...".

References:
 - Ref.[1] has been published - please update.
 - Ref.[4] is incomplete.
 - Ref.[8] has been published - please update. (Note you have also a spurious arXiv listing.
 - Ref.[10] has been published - please update.
 - Ref.[15] is a CLAS Collaboration paper and should be listed as such.
 - Ref.[20] has been published - please update.
 - Ref.[31] has been published. Reference the published paper, not the thesis.