[Clascomment] OPT-IN:Multidimensional Measurements of Beam Single Spin Asymmetries in Semi-inclusive Deep-inelastic Charged Kaon Electroproduction off Protons in the Valence Region

[Daniel Carman]

Aron,

I have read through your paper draft on the beam spin asymmetry in K+ SIDIS and pass along my 
comments below. I have a number of general comments and a list of specific comments for your
consideration. Let me know if you have any questions.

Regards,
Daniel

---------------------------------------------------------------------------
General:
 - You are planning to submit this manuscript to PRL. I am concerned that the current form of
   your paper is too specialized, too jargon-filled, and too limited in appeal to have a high 
   probability of acceptance. In my comments below I provide my opinion on how you could improve
   the text for broader appeal.
   
Page 1:
 - Abstract.
   - Line 2. Use "... been performed with 10.2 and 10.6~GeV incident electron beams ...".
   - Line 5. Use "... transverse momentum, and photon ...".
   - Line 6. Use "kaon". Also this is the only place that you use the abbreviation "BSA". It
     is not introduced. Better to use "... kaon SIDIS single spin asymmetry in ...".
   - Line 7. Use "The data provide constraints on ...".
 - Line 16. Use "... and their spatial distribution ...".
 - Line 22. Use "twist-$t$" and "2-$t$".
 - Line 23. Use "... process through which ...".
 - Line 26. Use "... and gluons that describe the ...".
 - Line 30. Use "well-established".
 - Line 40. Use "... measured by COMPASS [14], ...".
 - Line 50. Use "... energies typical for fixed-target experiments.".
 - Paragraph at line 52. It would be good to provide some context about studies of K+ vs.
   studies of pi+. What can we learn by studying different mesons in SIDIS process? What
   is special about pseudoscalar mesons in particular?
 - Line 53. Use "$K^+$".
 - Line 61. Use "... of the hadron with respect to ...".
 - Line 63. Use "A schematic illustration ...".
 - Line 65. You use the variable "y" here but you have not defined it yet.
 - Line 66. Use "$P_T$".
 - Line 69. Use "where $d\sigma^\pm$ are the differential cross sections for ...".
 - Line 70. Use "{\it i.e.}".

Page 2:
 - Line 71. Use "The $L$ and $U$ ...".
 - Line 73. Use "... target, respectively.".
 - Line 75. Use "Fig.~1". The tilde keeps the "Fig." and the "1" together without breaking this
   across lines.
 - Eq. 2. End this equation with a period for proper punctuation.
 - Line 81. Do not indent this line. Use "... from the longitudinal ...".
 - The paragraph stretching from line 84 to line 133 is one that I strongly urge you to revisit.
   This text and specifically Eq. 3 are impenetrable for the non-expert. I would spend a few
   sentences to better introduce and motivate Eq. 3 and its ingredients. Then find a more digestible
   manner in which to introduce and define the terms. Without being able to appreciate Eq. 3, the
   rest of the paper will not make much sense.
 - Line 87. Use "... the kinematic regime where the ...".
 - Eq. 3. End this equation with a period for proper punctuation.
 - Line 90. Do not indent this line.
 - Line 91. Use "... a kinematic factor, $e$ is a twist-3 PDF, $H_1^\perp$ is the Collins FF, ...".
 - Line 95. Use "... $h_1^\perp$ is the Boer-Mulders function ...".
 - Line 96. Use "... Refs. [12,13,19].".
 - Line 108. Use "... only terms where either ...".
 - Line 129. Use "... through the QCD equations of motion ...".
 - Line 139. Use "... longitudinally polarized and the target was ...".
 - Line 141. Use "... 10.2 and 10.6~GeV.".

Page 3:
 - Line 166. Use "... $y < 0.75$, and on ...".
 - Line 176. Use "... CLAS [15], and CLAS12 [16] for different mesons in the final state over the ...".
 - Line 178. "the contribution of each part." Each part of what? I cannot understand the point that you
   are trying to make.
 - Line 187. Use "... bins in the $Q^2 - x_B$ plane.".
 - Line 188. Use "In each $Q^2$ - x_B$ bin ...".
 - Line 196. Use ".. in a specific bin $i$ as:".
 - Eq. 4. End this equation with a period for proper punctuation.
 - Line 197. Do not indent this line.
 - Line 198. Use "... polarimeter upstream of CLAS12 to be 87.24\%$\pm$2.42\%.".
 - Line 207. Use "... ($\sim$4\%), and contamination from ...".
 - Line 208. Use "The influence of additional $\cos \phi$ and $\cos 2\phi$ azimuthal modulations
   on the extracted ...".
 - Line 210. Use "... also evaluated and found to ...".
 - Line 221. Use "... and the uncorrected kaon ...".
 - Line 224. Use "... for the kaons. Every other part ...".
 - Line 228. The term "PID" has not been defined.
 - Line 236. Use "... extracted and is listed in ...".
 - The supplemental material was not distributed with the paper. Please make this available for review
   and comment.
 - Line 239. Use "... kinematic variables in each bin.".
 - Line 242. Use "Figures~3 and 4 show ...".
 - Line 243. Use "$x_B$ for $eK^+X$.".
 - Line 244. Use "... the general $P_T$ and $z$ behavior ...". Your text looks like you are discussing
   the ratio of variables.

Page 4:
 - Figures 3 and 4. The long-dashed lines cannot be seen. They are in fact coincident with the solid
   red lines. Is there value added in including them on the plot when model 1 is essentially just
   $eH_1^\perp$?. The dashed lines are all coincident with zero? Is there value added included them on
   the plots when you can just say that $g^\perpD_1$ is consistent with zero?
 - Fig. 3 caption.
   - Line 1. Use "$K^+$".
   - Line 2. Use "$Q^2 - x_B$ bins".
   - Line 4. Use "... 0.37 (see Fig. 2.)).".
   - Line 10. Use "... in Refs. [40,41].".
 - Line 251. Use "... to the chosen kinematic binning.".
 - Line 253. Use "... axial-vector diquark.".
 - Line 256. Use "... ratio for the axial-vector ...".
 - Line 258. Use "... axial-vector diquark and ...".
 - Line 260. Use "... described in Ref. [42].".
 - Line 261. Use "... provide any uncertainties, only ...".
 - Line 263. Use "$Q^2 - x_B$ bins".
 - Fig. 4 caption.
   - Line 1. Use "$K^+$".
   - Line 2. Use "$Q^2 - x_B$ bins".
 - Line 268. Use "... uniformly negative, which is ...".
 - Line 283. Use "higher-twist".
 - Line 288. Use "... to Ref. [43], global fits ...".
 - Line 289. Use "... Drell-Yan data indicate that this may ...".

Page 5:
 - Line 301. "a strong drop can be observed". A strong drop in what? I cannot make sense of your
   comment.
 - Line 312. Use "kaon".

References:
 - Your bibliography needs much attention.
 - Your style is not consistent from entry to entry. You give titles for some entries but not all.
   You spell some journal names out completely and you use abbreviations for others. For many you
   do not give the author's name(s), but just initials. You give URLs for a few but not all.
 - Ref.[28] is not proper. You need a complete reference here.
 - Ref.[34] should be "V.D. Burkert {\it et al.} ({\it CLAS Collaboration}), ...".
 - Ref.[17] uses "The HERMES Collaboration". Ref.[18] used "HERMES Collaboration". Similarly for
   Refs.[15] and [16]. The standard style drops the "The".