[Clascomment] OPT-IN: Double-pion electroproduction off protons in deuterium: quasi-free cross sections and final state interactions

[Daniel Carman]

Dear Iuliia, Ralf et al.,

I have read through the draft of your e1e analysis paper on exclusive two pion production 
off the deuteron. My comments are mainly on grammar/clean-up as opposed to physics. You have done a significant amount of work to complete this analysis and your thoroughness is apparent. I find your presentation style complete and clear. I include my comments below. If you have any questions, let me know. If you would like me to review an updated version of the paper, I am happy to help.

Regards,
Daniel

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General:
 - My biggest issue with the paper in terms of grammar is the use of the present verb tense in
   most places throughout. The paper should be written with most verbs of work done in the past
   tense. This explains why my comment list appears to be quite lengthy.
 - Use "{\it e.g.}" and "{\it i.e.}" throughout.
 - You use "Sect." as an abbreviation for Section. Better to use "Section" or "Sec.".
 - In many instances, you put subscripts in roman font. I find it less "clunky" to use math
   mode, e.g. "$F_{fsi}$" and not "$F_{\rm fsi}$".
 - A quirky rule in english regarding hyphens, you do not use them to connect a modifier ending
   in "-ly". So, e.g., use "fully integrated cross sections" and not "fully-integrated cross
   sections".
 - PRC does not use the "(Color online)" qualifier in figure captions any longer. These can all
   be dropped.

Page 1:
 - Line 18. Use "... experimental data, as well as ...".
 - Line 21. Use "Exclusive reactions off free ...". (Drop the "By now".)
 - Line 26. Use "... have become available.".
 - Line 36. You mention the scarcity of electroproduction data off the neutron. Why have you not
   cited the Ye Tian paper here? I believe you should.
 - Line 51. Use "... of electron scattering off ...".
 - Line 56. Use "This analysis covers ...".
 - Line 64. Use "... features that are not ...".
 - Line 66. I do not think it is proper to capitalize "Final State Interactions".
 - Line 67. I do not like the shorthand of "final hadrons". I prepare "final state hadrons". However,
   if you stick with this usage, the placement of footnote #3 on pp. 19 is ill-considered. Move the
   footnote to the first time you introduce this shorthand.
 - Line 70. Use "This paper presents ...".
 - Line 73. Use "... measurements were performed ...".

Page 2:
 - Line 110. No need to repeat Refs. [15] and [16] here as you just listed them on line 106.
 - Line 120. Use "Refs. [15],[16],".
 - Line 121. Use "... proportion of events in which FSIs ...".
 - Line 136. Use "... this study was conducted ...".
 - Line 141. Use "liquid-deuterium target".
 - Line 144. Do not use "good fraction". Be quantitative.
 - Lines 147-153. Most of this has already been stated. I would drop this entire paragraph. Instead, modify
   the sentence on line 137 to be "... of the ``e1e" run period that took place from November 2022 until
   January 2023.".
 - Line 155. Use "... detector was based ...".
 - Line 156. Use ".. field that was generated by ...".
 - Line 158. Use "... field bent charged particles ...".
 - Line 161. Use "... but left the azimuthal ...".
 - Line 162. Use "... setting was to bend negatively charged particles toward ...".
 - Line 165. Use "... naturally separated the ...".
 - Line 167. Use "Each sector included ...".
 - Line 171. Use "... CLAS was limited only ...".
 - Line 172. Use "... and was approximately 90\% at backward polar angles and ...".
 - Line 174. Use "... coverage spanned from ...".
 - Lines 178-180. Drop the sentence "The Drift Chambers ...".
 - Line 181. Use "The Drift Chambers performed charged particle tracking, ...".
 - Line 183. Use "... curvature of their trajectories through the magnetic field.".
 - Line 183. Use "... sub-detectors were located ...".
 - Line 185. Use "... traveled through them ...".

Page 3:
 - Line 187. Use "... Counters were located ...".
 - Line 188. Use "... and served ...".
 - Line 190. Use "... scintillators were located ...".
 - Line 193. Use "... measured the time ...".
 - Line 195. Use "With the particle momentum known ...".
 - Line 197. Use "... which allowed for particle identification [22],[23].".
 - Line 199. Use "... Calorimeter were triggering ...".
 - Line 200. Use "... of electrons, as well ...".
 - Line 203. Use "... sectors were equipped ...".
 - Line 204. Use "... that collected the ...".
 - Line 205. Use "... and stored the ...".
 - Line 209. Drop the sentence "For this particular part ..." as you have already stated this.
 - Line 211. Do not begin a new paragraph here. Use "The target had a ...".
 - Line 212. Use "... which served the ...".
 - Line 215. Use "... either originated from the beam and/or came from ...".
 - Line 217. Use "... the bubbles drained ...".
 - Line 218. Use "... of the target, thus ...".
 - Line 233. Use "... were distinguished among ...".
 - Line 242. Use "... yield was adjusted ...".
 - Line 246. Use "... simulation was performed.".
 - Line 247. Use "... events were generated ...".
 - Line 252. Use "... events were passed ...".
 - Line 254. Use "The procedure included ...".
 - Line 258. Use "... that survived this ...".
 - Line 259. Use "They were analyzed ...".
 - Line 262. Use "... candidate was defined ...".
 - Line 263. Use "... that had signals ...".
 - Line 266. Use "... were required.".
 - Line 279. Use "... cut was chosen ...".
 - Line 281. Use "To eliminate part of the pion contamination, an EC sampling fraction ...".
 - Line 282. Use "... cut was applied based on the ...".

Page 4:
 - Line 299. Use "... that was determined ...".
 - Line 300. Give width of cut (+/- 3 sigma?).
 - Line 302. Use "Additionally, to further improve the ...".
 - Line 304. Use "... was analyzed ...".
 - Line 312. Use ".. CC was to separate ...".
 - Line 315. Use "... cuts was applied:".
 - Line 322. Use "Each of these cuts, except the last one, was defined ...".
 - Line 324. Use "... were defined.".
 - Line 326. Use "... Refs. [27],[28].".
 - Line 327. Use "... plane was taken ...".
 - Line 329. Use "... procedures were based on the studies of Refs. [27] and [30].".
 - Line 330. Use "... matching was based ...".
 - Line 340. Use "... conditions were removed. Events with signals from both PMTs were kept.".
 - Line 343. Use "... cut was applied.".
 - Line 348. Use "... lines were treated ...".
 - Line 351. Use "... CC showed low ...".
 - Line 352. Use "... electron hit such a ...".
 - Line 353. Use "... photoelectrons was significantly ...".
 - Line 354. Use "This lead to a ...".
 - Line 358. Use "... zones were distributed ...".
 - Line 359. Use "... simulation did not ...".

Page 5:
 - Fig. 3 caption. Line 3. Use "... lines were treated ...".
 - Line 361. Use "... removes these inefficient zones was applied.".
 - Line 362. Use "... in Refs. [15],[16],[28],[31].".
 - Line 373. Use "low-lying".
 - Line 375. Use "high-lying".
 - Line 380. Use "... photoelectrons was applied, ...".
 - Line 382. Use "... position was individually ...".
 - Line 385. Use "... cut was performed ...".
 - Line 387. Use "... was applied, ...".
 - Line 390. Use "... in Refs. [15],[16],[28],[31].".
 - Line 392. Use "Hadrons were identified ...".
 - Line 394. Use "... which allowed the ...".
 - Line 396. Do not begin a new paragraph here. Use "... hadron was identified ...".
 - Line 399. Use "... is termed the nominal value that was calculated ...".
 - Fig. 4 caption. Line 5. Use "... red curves were treated ...".
 - Line 403. Use "... distributions were examined ...".
 - Line 405. Use "... counters, the distributions were ...".
 - Line 409. Use "... in Refs. [28],[31], ...".
 - Line 418. Use "... curves were selected ...".
 - Line 419. Use "... cuts were performed ...".

Page 6:
 - Line 432. Use "... loss was included ...".
 - Line 437. Use "... which was then applied ...".
 - Line 448. Use "... the effect was discernible ...".
 - Line 456. Use "... part of the ``e1e" dataset ...".
 - Line 460. Use "... include an electron ...".
 - Line 461. Use "... as well as an electron ...".
 - Line 468. Use "... coils were not equipped ...".
 - Line 471. Use "... area was further ...".
 - Line 477. Use "... from the coils, ...".
 - Line 484. Use "... cuts were applied ...".
 - Line 491. Use "Data quality checks".
 - Line 498. Use "... cuts on the Data ...".
 - Line 499. Use "... and the number of events per Faraday Cup (FC) charge were used.".
 - Line 501. Use "... charge updated ...".
 - Line 510. Use "... live time, as well as ...".
 - Line 511. Use "... charge, were examined ...".
 - Line 513. Use "... demonstrated large fluctuations were excluded from ...". Also, be quantitative here. What does "large" mean?
 - Line 515. Use "... in Refs. [15],[16].".
 - Line 516. Use "... also Refs. [28],[31].".
 - Line 519. Use "... with liquid deuterium, as well as ...".
 - Line 530. Use "... demonstrate a well-separated peak ...".

Page 7:
 - Fig. 5 caption. Line 4. Use "Both the full and empty ...".
 - Line 537. Use "liquid-deuterium".
 - Line 555. Use "... two topologies were ...".
 - Line 561. Use "... CLAS did not cover ...".
 - Line 564. Use "... impacted registration ...".
 - Line 565. Use "... were bent into ...".
 - Line 566. Use "This lead to a ...".
 - Line 568. Use "... prevented registration ...".
 - Line 575. Use "... also suffered from ...".
 - Line 580. Use "... has a tolerable number ...". Also, what defines "tolerable"? Be quantitative.
 - Line 596. Use "... pair was produced ...".
 - Line 600. Use "... reconstruction failed to ...".
 - Line 605. Use "... production of a $\pi^+\pi^-$ pair ...".
 - Line 607. Use "... state were registered.".
 - Line 609. Use "... demonstrated a strong admixture ...".
 - Line 610. Use "... circumstances prevented the ...".
 - Line 614. Use "... features that are not ...".

Page 8:
 - Line 620. Use "... proton was not ...".
 - Line 622. Use "... had to be applied ...".
 - Line 624. Use "... which lead to ...".
 - Line 631. Use "... distributions reproduce the Fermi ...".
 - Line 633. Use "... motion be properly ...".
 - Line 638. Use "... electroproduction off a ...".
 - Line 652. Use "... masses), thus complicating ...".
 - Line 663. Use "... had to be developed.".
 - Line 671. Use "... identification was performed ...".
 - Line 3 after line 688. Use "... Eq.(2) were used.".
 - Line 689. Do not begin a new paragraph on this line.
 - Line 690. Use "... of particle $i$. Both quantities were calculated ...".
 - Line 695. Use "... hadrons were registered.".
 - Line 699. Use "... 100-MeV-wide bin in $W$.".
 - Fig. 6 caption. Line 7. Use "... $W$ were calculated ...".
 - Line 701. Use "... perfectly matches the ...".

Page 9:
 - Line 718. Use "... was measured, ...".
 - Line 719. Use "... it was not used ...".
 - Line 721. Use "... four-momentum was instead ...".
 - Line 722. Use "... that was calculated ... thus was Fermi ...".
 - Line 4 after line 725. Use "... identification was therefore".
 - Line 6 after line 725. Use "... which was calculated ...".
 - Line 726. Use "... of particle $i$ and ...".
 - Line 2 after line 727. Use "... procedure was developed, ...".
 - Line 3 after line 727. Use "... quantity was used to ...".
 - Line 743. Use "... admixture was performed, which included ...".
 - Line 746. Use "... were fit by a ...".
 - Line 751. Use "... curves were summed ...".
 - Line 1 after line 753. Use "... was determined for ...". Also given your "FSI" usage, I prefer "$F_{FSI}$" (uppercase subscript).
 - Line 754. Use "... yield was multiplied ...".
 - Line 755. Use "... which served as ...".
 - Line 758. Use "... was assumed to be ...".
 - Line 760. Use "... variables was neglected ...".
 - Line 764. Use "... correction was not ...".

Page 10:
 - Line 767. Use "... in Fig. 7, accompanied by the corresponding correction, accounts ...".
 - Line 772. Use "... including the minor ...".
 - Line 797. Use "... this information was not ...".
 - Line 804. Use "... assumption was used ...".
 - Line 812. Use "... events were selected ...".
 - Line 816. Use "... were then used ...".
 - Line 818. Use "... sections were extracted ...".
 - Line 824. Use "... as the system where the ...".
 - Line 852. Use "... momentum was accessible ...".
 - Line 855. Use "... information was irrevocably lost ...".
 - Line 859. Use "... transformation could not be performed.".
 - Line 862. Use "... at rest was used.".
 - Line 863. Use "... and was employed ...".

Page 11:
 - Line 867. Use "... this effect was included ...".
 - Line 871. Use "... particles were defined ...".
 - Line 872. Use "... into the CMS, the kinematic variables ... \pi^-$ were calculated.".
 - Line 876. Use "... they were chosen ...".
 - Line 882. Use "... variables was used ...".
 - Line 887. Use "the first hadron ...".
 - Line 892. What does "defined by the three-momenta of all final hadrons" mean? Two vectors define a plane, but there is not
   a plane containing all three vectors.
 - Line 894. Use "... sections were obtained ...".
 - Line 906. Use "... distribution was filled ...".
 - Line 907. Use "... events that survived ...".
 - Line 910. Use "... sections were extracted.".
 - Line 922. Use "... variable was divided ...".
 - Line 924. Use "... $W$ subranges in order to ...".
 - Fig. 8 caption. Line 2. Use "... section was calculated ...".

Page 12:
 - Line 937. Do not begin a new paragraph with this line.
 - Line 939. Use "... section was calculated ...".
 - Line 940. Use "... was not distinct.".
 - Line 942. Use "... was calculated using ...".
 - Line 943. Use "... which caused events ...".
 - Line 948. Use "... bin was set ...".
 - Line 954. Use "... bin was kept ...".
 - Line 956. Use "... that were obtained ...".
 - Line 977. Use "liquid-deuterium".
 - Line 985. Use "liquid-deuterium" and "empty-target".

Page 13:
 - Line 1 after line 998. Use "... analysis was to ...".
 - Line 5 after line 998. Use "... approximation is connected ...".
 - Line 1 after Eq.(12). Do not begin a new paragraph with this line.
 - Line 1005. Use "... was first obtained ...".
 - Line 1008. Use "... sections were obtained.".
 - Line 2 after line 1008. Use "... sections were extracted ...".
 - Line 4 after Eq.(14). Use "... given in Eq.(15), where ...".
 - Line 1009. Use "... row in Eq.(15), note ...".
 - Line 1011. Use "... sections were calculated ...".
 - Line 1017. Use "... simulation was performed ...".
 - Line 1020. Use "... electroproduction off a ...".
 - Line 1027. Use "... TWOPEG-D were passed ...".
 - Line 1043. Use "... events were generated ...".
 - Line 1050. Use "... value at that point.".
 - Line 1051. Use "... Eq.(10) was then ...".

Page 14:
 - Line 1060. Use "... could not be reliable ...".
 - Line 1066. Use "... was performed that ...".
 - Line 1069. Use "... cells, were subject to ...".
 - Line 1082. Use "... study of Refs. [15],[16], which also set the ...".
 - Line 1099. Use "... cells was determined ...".
 - Line 1101. Use "... cell was treated as empty if it contained generated ...".
 - Line 1102. Use ".. but did not contain ...".
 - Line 1105. Use "... were also treated as empty ...".
 - Line 1112. Use "... cells were filled with ...".
 - Line 1114. Use "These events were subject to ...".
 - Line 1116. Use "The scaling was performed ...".
 - Line 1133. Use "... section was kept ...".
 - Line 1142. Use "... sections was followed ...".
 - Line 1146. Use "Radiative corrections".
 - Line 1152. Use "... be taken directly into account ...".

Page 15:
 - Line 1157. Use "... correction was performed ...".
 - Line 1165. Use "... approach was applied ...".
 - Line 1169. Use "... photons are emitted collinearly either ...".
 - Line 1179. This is a weak argument. You are effectively saying that the assumption on the computation of
   the "hard" part is deemed adequate because no approaches are available. Please revisit this statement.
 - Line 1 after line 1183. Use "... Eq.(10) was determined ...".
 - Line 3 after line 1183. Use "... effects were generated ...".
 - Line 5 after line 1183. Use "... events were subjected to ...".

Page 16:
 - Line 1 on page. Use "... Eq.(17) was taken in ...".
 - Line 1184. Do not begin a new paragraph with this line.
 - Line 1187. Use "... were subject to any ...".
 - Line 1207. Use "... of both the integral and ...". I think that the appropriate term here is "integrated" not
   "integral". Please check usage throughout.
 - Line 1220. Use "... was performed by ...".
 - Line 1229. Use "... in the studies where experimental ...".
 - Line 1240. Use "... $W$ was used for ...".
 - Line 1241. Use "... transformation was applied, so ...".
 - Line 1 after line 1243. Use "... correction was performed ...".
 - Line 4 after line 1243. Use "... section was divided by ... that was calculated as".
 - Line 1248. Do not begin a new paragraph with this line.
 - Line 1260. Use "... correction was attributed ...".

Page 17:
 - Line 1265. Use "... value was then assigned ...".
 - Line 1269. Use "... correction was applied ...".
 - Line 1271. Use "Due to the relatively ...".
 - Line 1275. Use "data points".
 - Line 1287. Use "... uncertainties were considered, ...".
 - Line 2 after line 1293. Use "... data was calculated ...".
 - Line 2 after line 1296. Use "... statistics was estimated ...".
 - Line 2 after line 1315. Use "... (20) were combined ...".
 - Line 1316. Do not begin a new paragraph with this line.
 - Line 1320. Use "... $alpha_{h1}$) was obtained ...".
 - Line 1329. No comma after "uncertainty type".

Page 18:
 - Line 1340. Use "... bins in the final ...".
 - Line 1341. Use "... uncertainties were estimated ...".
 - Line 1353. Use "... sections was estimated ...".
 - Line 1376. Use "... uncertainty was assigned ...".
 - Line 1379. Use "... sections were extracted ...".
 - Line 1381. Use "... sections were found ...".
 - Line 1391. Use "... include uncertainties due to the shapes ...".
 - Line 1392. Use "... that were used in ...".
 - Line 1395. Use "... uncertainty performed in this study excludes ...".
 - Line 1401. Use "... value was set to ...".
 - Line 1403. Use "... sections were also calculated ...".
 - Line 1409. Use "... cut was estimated ...".
 - Line 1410. Use "... and was found to be ...".
 - Line 1414. Use "... correction was performed ...".
 - Line 1420. Use "... factor was estimated ...".
 - Line 1422. Use "... values was used for ...".
 - Line 1424. Use "... factor was estimated as the standard ...".
 - Line 1426. Use "... uncertainty was estimated ...".
 - Line 1428. Use "... correction was estimated for ...".
 - Line 1429. Use "... correction was applied.".
 - Line 1434. Use "... uncertainty was assigned ...".

Page 19:
 - Line 1437. Use "... sources were summed ...".
 - Line 3 after line 1443. Use "... respectively, were combined ...".
 - Line 1447. Use "... sections was obtained ...".
 - Line 1450. Do not begin a new paragraph with this line.
 - Line 1466. Do not begin a new paragraph with this line.
 - Line 1480. Do not begin a new paragraph with this line.
 - Line 1481. Use "... between the hadrons, as well as far ...".
 - Line 1484. Do not begin a new paragraph with this line.
 - Line 1508. Do not begin a new paragraph with this line.
 - Footnote #4. Use "... denotes the neutron, ...".

Page 20:
 - Line 1530, 1551, Fig. 11 caption line 3. I do not think the word "agglomerations" is appropriate here based
   on context. An agglomeration is a mass or collection of things. Please revisit.
 - Line 1568. Use "To better understand the redistribution ...".
 - Line 1570. Use "... distributions were examined ...".

Page 21:
 - Line 1598. Use "For reactions occurring ...".
 - Line 1600. Use "... have a different impact on $M_{X[i]}^2$ ...".
 - Line 1644. Use "... sections was obtained ...".
 - Line 1645. Use "... example, Fig. 15 shows the ...".

Page 22:
 - Fig. 14 caption. Line 4. Use "... by the solid curves ...". 
 - Line 1653. Use "... from events in which the ... neutron is reduced to the kinematically ...".
 - Line 1661. Use "In general, the admixture ...".

Page 23:
 - Line 1697. Use "... procedures were applied ...".
 - Line 1701. Use "... TWOPEG were normalized ...".
 - Line 1711. Use "... from Refs. [15],[16].".
 - Line 1720. Use "$(W,Q^2)$".
 - Line 1729. Use "... from Refs. [15],[16] ...".

Page 24:
 - Fig. 16 caption. Line 2. Use "Refs. [15],[16]".
 - Line 1738. Use "... measurement were considered, ...".
 - Line 1739. Use "... effects were assumed ...".
 - Line 1742. Use "... of Refs. [15],[16].".
 - Line 1743. Use "The ratio was fit with a fourth-order polynomial.".
 - Line 1749. Use "... near the threshold, as well as in the dip region between the two integral resonance peaks
   at about $W$ = 1.5~GeV - 1.6~GeV". I also think that you mean "two integrated resonance peaks".
 - Line 1754. Use "... ratios were obtained ...".
 - Line 1761. Use ".. fit with a fourth-order polynomial ...".
 - Line 1769. Do not begin a new paragraph with this line.

Page 25:
 - Fig. 17 caption. Line 2. Use "Refs. [15],[16]. Rows from ... ratios were averaged ...".
 - Fig. 18 caption. Line 1. Use "... proton analogs from Refs. [15],[16].".
 - Fig. 18 caption. Line 3. Use "The ratios were averaged ...".

Page 26:
 - Line 1780. Use "The ratios were ...".
 - Line 1781. Use "$(W,Q^2)$".
 - Line 1793. Do not begin a new paragraph with this line.
 - Line 1805. Use "... from events in which ...".
 - Line 1832. Do not begin a new paragraph with this line.
 - Line 1834. Use "The measurements were performed ...".
 - Line 1836. Use "1.3~GeV".
 - Line 1837. Use "0.4~GeV$^2$".
 - Line 1839. Use "... statistical uncertainties, and modest ...".
 - Line 1841. Use "... of events in which the final ...".
 - Line 1856. Use "... techniques were developed, ...".
 - Line 1869. Use "... FSI-background was performed ...".
 - Line 1877. Use "... from events in which ...".
 - Line 1889. Add a space between lines 1888 and 1889.

References:
 - Use "(CLAS Collaboration)" and not "(CLAS)".
 - Do not include arXiv information for already published papers.
 - [4]. This is not a CLAS Collaboration paper.
 - [5]. No quotes about "CLAS Physics Database".
 - [23]. First author is "G. Mutchler".
 - [24]. No quotes about "e1e target assembly".
 - [44]. Add spacing in journal name "Rev. Mod. Phys.".