[Clascomment] OPT-IN:Hard exclusive pion electroproduction at backward angles with CLAS

[Daniel Carman]

Dear Kijun,

I have read through your paper draft on pion electroproduction at back
angles. The paper is in reasonable shape, but there are some comments
that I have from my reading. Let me know if you have any questions.


			   Regards,

				  Daniel

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Page 1:
 Abstract.
  - Line 2. Use "... at backward pion center-of-mass angles.".
  - Line 3. Use "cross sections".
  - Line 5. Use "... (TDAs) and shed new ...".
 - Line 2. Use "... has significantly increased ...".
 - Line 9. Use "... variables such as the parton ...".
 - Line 22. Use "... transfer and $m_p$ is ...".
 - Line 22. This first paragraph is unwieldy. Begin a new paragraph with the
     sentence "The left panel of Fig. 1 ...".
 - Line 35. Use "... of GPDs, i.e. the ...".
 - Line 54. Use "... variable $\xi$ and $u$.".
 - Line 55. Use "... constraint $\Sum_{i=1 \to 3} = 2 \xi$, ..."
 - Line 65. Use "... state of the nucleon, ...".
 - Line 67. Use "... see {\it e.g.} Ref.[14]), ...".

Page 2:
 Fig. 1 caption.
  - Line 16. Use "parametrizing".
  - Lines 17, 18. Remove the two semicolons.
 - Line 100. Use "... where $\Delta_T$ is the ...".
 - Line 104. Use "... \Delta_T^2$, then ...".
 - Line 107. Use "... depend are integrated ...".
 - Line 115. The run period is called e1-6, not e1-6a.
 - Line 116. Use "CLAS was built ...". You should properly use past tense in what
    follows. I have tried to catch all of the tense issues below.
 - Line 119. Use "... magnet were independently ...".
 - Line 120. Use "... for charged particle tracking, ...".
 - Line 126. Use "... EC was segmented ...".
 - Line 128. Use "CLAS covered nearly the full ...".
 - Line 130. Use "... acceptance was maximum ...".
 - Line 131. Use "... and decreased at forward angles. The e1-6 run had the
     maximum electron ...".
 - Line 132. This sentence is a bit awkward to me. I suggest "... beam energy
      for the JLab accelerator, which allowed us to reach ... and the maximum
      CLAS torus magnetic field (current = 3375~A), which allowed us ...".
 - Line 137. Use "... we detected the scattered electron and the final state pion
      in CLAS.".
 - Line 143. Use "... given in Ref.[19] ...".
 - Line 145. Again, another seemingly endless paragraph. Begin a new paragraph
    with the sentence "Although the kinematics ...".
 - Line 146. Use "... particles was a bit ...".

Page 3:
 - Line 153. Use "... EC energy, corresponding ...".
 - Line 157. Use "... in the CC and ...".
 - Line 160. Use "... which could reliably ...".
 - Line 162. Use "... by the time-of-flight technique ...".
 - Line 167. Use "... momenta of the particles ...".
 - Line 168. Use "... due to misalignments ...".
 - Line 178. Use "... peak was due to ...".
 - Line 187. Use "... was based on ...".
 Fig. 2 caption.
  - Line 2. Use "... neutron missing mass peak fit.".
  - Line 3. Use "... 0.25 and ...".
  - Line 6. Use "... background and the green ...".
 Fig. 2. I am not sure that the parameters P2BG and P3BG (not discussed in the
   text) should be printed on this figure.

Page 4:
 - Line 205. Begin a new paragraph at this point to break up the very long
     structure.
 - Line 205. Use "... $\sigma_{LT}$ and $\sigma_{TT}$ ...".
 - Line 206. Use "... at a given $W$ ...".
 - Line 207. Use "... $\sigma_{LT}$ and $\sigma_{TT}$ ...".
 - Line 208. Use "... from the experimental data ...".
 - Line 215. This sentence makes no sense as written. How about "The cut values,
     bin sizes, and fitting functions were varied in order to test ..."?
 - Line 219. Use "... identification was estimated ...".
 - Line 224. Use "... 1.0~GeV$^2$, resulting in ...".
 - Line 226. Use "... in $varphi_\pi^*$, which resulted ...".
 - Line 229. Use "... target were estimated ... 1\%, respectively.".
 - Line 230. Use "... uncertainty was estimated ...".
 - Line 231. Begin a new paragraph with the sentence "We extracted the ...".
 - Line 239. Use "... $\chi^2$ per degree of freedom ... fits was $\sim$2.6, ..."
 - Line 240. So, what about the highest Q2 point? You have not completed your
     thought here. The value of chi2 for this last point was?
 - Line 240. Use "Since the CLAS acceptance showed ...".
 - Line 241. Use "... complicated $\varphi_\pi^*$-dependence around
    $\varphi_\pi^* \sim 0$, we ...".
 - Line 243. Use "... in the acceptance ...".
 - Line 244. This sentence leaves the reader hanging. What was the additional
     systematic added to these points in the fit (beyond the already estimated 12%)?
 - Line 252. Use "... $\sigma_{TT}$ and $\sigma_{LT}$.".
 - Line 253. Use "cannot".
 Fig. 3 caption.
  - Line 6. Use "... show the full fit ...".
 - Line 265. Use "... for the nucleon DAs ...".
 - Line 270. Use "... are the predictions ...".
 - Line 278. Use "... of Ref.[29], ...".

Page 5:
 Fig. 4 caption.
  - Line 2. Use "... $\square$) and $\sigma_{LT}$ ... $Q^2$. The inner error
      bars ...".
  - Line 3. Use "... and the outer error bars are the total ...".  
  - Line 4. Use "The curves are ...".
 - Line 290. Use "... was provided by ...".
 - Line 292. Use "... that encode ...".
 - Line 293. Use "... goal was an ...".
 - Line 299. Use "... not incontrovertible ...".
 - Line 302. Use "... of Laget [27] yield ...".
 - Line 306. Use "... rules that lead to ...".
 - Line 308. Use "... $\sigma_{LT}$ and $\sigma_{TT}$.".
 - Line 309. Use "... tests require both ...".
 - Line 322. Use "... in other reactions, which can ...".
 - Line 323. Use "... 35] and J-PARC ...".
 - Line 324. Use "... at JLab [37].".

References:
 - [12]. Use "... Pire and L. Szymanowski, ...".
 - [13]. Use "... Pire and L. Syzmanowski, ...".
 - [15]. Use "... -Shansky and L. Syzmanowski, ...".
 - [16]. Use "J.P. Lansberg, B. Pire, ... Shansky and L. Syzmanowski, ...".
 - [18]. Use "B.A. Mecking ...".
 - [19]. Use "... al.} [CLAS Collaboration], ...".
 - [20]. Use "... al.} [CLAS Collaboration], ...".
 - [22]. Use "... D {\bf 66}, ...".
 - [24]. Use "... Phys. Rev. ...".
 - [25]. Use "... Ogloblin and I.R. Zhitnitsky, ...".
 - [28]. Use "... al.}, Phys. Rev. D {\bf 14}, 679 ... {\it et al.}, Phys. Rev.
      D {\bf 49}, ...".
 - [29]. Use "J.M. Laget, Phys. ...".
 - [30]. Use "... Airapetian {\it et al.}, Phys. Lett. B {\bf 659}, ...".