[Clascomment] OPT-IN:Single and double spin asymmetries for deeply virtual Compton scattering measured with CLAS and a longitudinally polarized proton target

[Daniel Carman]

Silvia et al.,

I have read through the draft DVCS paper dated Dec. 12. For the most part I think the
paper is well constructed, but I have a list of suggestions to improve the readability.
Let me know if you have any questions.


					        Regards,
						
						Daniel

************************************************************************************
General.
 - You are not consistent with your usage of speed of light units in this paper. I suggest that
   you let c=1 throughout.
 - With Figures that are in color, you need to begin the caption with "(Color online)". You have
   not done this consistently throughout.

Page 1.
 - Abstract.
   - Line 1. Use "double-spin"
   - Line 2. Here you use a prime notation on the final state e and p, but you do not use this notation
     elsewhere in the paper. I would drop it here for consistency.
   - Line 4. Use "... in the valence quark region."
   - Line 8. Use "... Form Factors, which give insight into ...".
 - Line 19. Use "... particles that form ...".
 - Line 33. Use "... research, from the perspective ...".
 - Line 40. Use "... articles, general reviews on GPDs, and details ...".
 - Line 50. Use "four-momenta".
 - Line 60. Use "... that can be treated ...".
 - Line 65. Use "..., which account for the ...".

Page 2.
 - Eq.(6). Upper bound on integral should be "1" and not "+1" for consistency. Also you have not defined
    $\epsilon$.
 - Eq.(7). Problem with notation. You have the differential in the numerator of the integrand.
 - Line 104. Use "... F}$, can be obtained.".
 - Line 105. Do not begin a new paragraph with this line. It should be part of the previous paragraph.
 - Line 106. Typo on "deconvolute".
 - Line 120. Use "... in the past few years.".
 - Line 124. Use "... leading-order, ...".
 - Line 128. Use "Beam-charge asymmetries (BSAs), ...".
 - Line 131. Use "HERMES Collaboration".
 - Line 133. Use "... target-spin asymmetries (TSAs) analyzing ...".

Page 3.
 - Line 143. Use "... in this work, ...".
 - Eq.(9). $\alpha$ is not defined.
 - Line 152. Here you introduce $k$ and $k'$ as the incoming and scattered electron four-momenta. However, you already
    defined them on the pp. 1 as $e$ and $e'$. You shouldn't use different notation within the same paper for the
    same quantities.
 - Eq.(12),(13),(14). These equations are not well introduced. What are the $c_n$ and $s_n$ terms? Why are the sums 
    truncated to n=2 and/or n=3?
 - Line 179. Use "... the target polarization ("Longitudinally polarized", in this case), and which is given at twist-2 by:"
 - Eq.(15). Add comma after equation.
 - Eq.(17). Add comma after equation.

Page 4.
 - Eq.(19). Add comma after equation.
 - Line 221. "expected to be smaller than the known BH terms." Based on what? A reference or statement is needed here.
 - Line 241. Use "The magnet, which provided a uniform ...".
 - Line 277. Begin a new paragraph with "The beam was rastered ...".
 - Line 298. Use "... all of the formulae below, ...".

Page 5.
 - Fig. 5. This drawing is not technically correct due to the way the LAC modules are draw. They were only
   included in S1 and S2.
 - Line 299. I suggest "... superscript on the number of normalized DVCS events $N$ is the beam helicity ($b$) and
    the second sign is the target polarization ($t$).".
 - Line 302. What is meant by "Faraday-cup counts"? Perhaps you should use "charge" instead of "counts"?
 - Eq.(24). End this equation with a period not a comma.
 - Eq.(26). Remove the comma after the equation.
 - Line 319. Do not indent this line. Use "... is the analog of ...".

Page 6.
 - Line 329. Use "... were selected among all ...".
 - Line 330. Use "... 0.8~GeV, bu requiring that ...".
 - Line 331. Use "... energy deposited in the inner layers of the EC ...".
 - Line 341. Use "... is shown as a function of the momentum in Fig. 4.".
 - Line 347. Use "... by our particle identification (PID) cuts for ...".
 - Line 363. Use "... clusters could not be fully ...".
 - Line 367. Use "... also adopted to remove the edges of the detector and IC-frame ...".
 - Fig. 4 caption.
   - Line 1. Use "... (inner+outer layers), ...".
   - Line 2. Use "... momentum $p$ as a function of $p$ for ...".
 - Right column. Bullet #1. The momentum corrections go beyond just corrections for energy loss through the
     material layers, they also account for imprecise knowledge of the torus field and the positioning of the
     DC within the field.
 - Line 385. Use "... (GPP) that simulates ...".
 - Line 390. Use "... files in the same way as was done in ...".

Page 7.
 - Fig. 8 caption.
   - Line 1. Use "... vs. energy for neutrals measured by ...".
 - Line 393. Use "... which produced ...".
 - Line 400. Use "... V.3, were included for both ...".

Page 8.
 - Line 417. Use "... electroproduction that included a ...".
 - Line 423. Use "... V.7, were included for both ...".
 - Line 437. Use "... the four-momenta of the three final-state ...".
 - Line 448. Use "... to compute the angle $\phi$ between the leptonic ...".

Page 9.
 - Line 474. Use "... cuts that included:"
 - Line 484. Use "... from channels other than ...".
 - Line 516. Use "... comparisons of data/MC for the $ep\pi^0$ channel in the ...".
 - Line 527. "... thus following the shape of the CLAS kinematical acceptance." I have no idea what you are
     trying to say here.
 - Line 542. Use "... average value from the data of each of ...".
 - Line 543. Use "... variables for each bin.".
 - Line 544. Use "uncertainties" not "errors".
 - Line 545. Use "... central kinematics are chosen ...".

Page 10.
 - Line 562. Use "... were determined using ...".
 - Line 575. Use "... experiment was much smaller ...".
 - Line 576. Use "... dilution factor analyses ...".
 - Line 580. Use "... are shown as functions of ...".
 - Line 585. Use "... constant fit is still reasonable.".
 - Line 588. Use "... both the $ep\gamma$ and ... analyses, ...".

Page 11.
 - Fig. 13 caption.
   - Line 2. Use "... x_B$ space (bottom).".
 - Fig. 14 caption.
   - Line 1. Use "Dilution factor as a function ...".
 - Eq.(29). End equation with a period not a comma.
 - Line 602. Delete "is the experimental uncertainty". You have already said this above.
 - Line 603. Use "... beam helicity for a given ...".
 - Line 611. Use "... Eq.(28), $P_bP_t$ was calculated for each run part as the ...".

Page 12.
 - Line 620. Use "... beam and target for each polarization ..."
 - Line 621. Use "... alone for the two ...".
 - Line 623. Use "uncertainties" and not "errors".
 - Line 632. Use "... applying the $ep\gamma$ event ... and the DVCS exclusivity ...".
 - Line 633. Use "... $N_{ep\gamma}$ events that are not ...".
 - Line 635. Use "... events in which one of the two ...".
 - Line 649. Use "$N_{ep\pi^0}^{DATA}$ was extracted ...".
 - Line 664. Use "... effects of the fitted peaks coming from background events due to electron scattering on
     ${14}$N.
 - Line 681. Use "... 50\% (in the highest $t$, highest $x_B$, central $\phi$ range).

Page 13.
 - Fig. 15 caption.
   - Line 2. Use "... (middle), and two-photon invariant ...".
 - Line 708. Use "... are raw; no $\pi^0$ ...".
 - Line 712. Use "... free proton (blue points) ...".
 - Fig. 17 caption.
   - Line 3. Use "... and square blue points are ...".

Page 14.
 - Line 717. Use "... going from a proton to a carbon target."
 - Line 722. Use "... impact our result within the ...".
 - Line 729. Use "... via uncertainty-weighted averages for each four-dimensional ...".
 - Line 732. Use "... were performed for the three asymmetries.".
 - Line 739. Use "... which were separately deduced from ...".
 - Line 744. Use "... the asymmetries, the longitudinal ...".
 - Line 756. Use "... double-spin asymmetry,".
 - Line 771. Use "... positive, and never greater ...".
 - Line 773. Use "... is, on average, ...".
 - Line 775. Use "... small values for $A_{UT}(0)$, ...".
 - Line 782. Use "... statistical uncertainties.".
 - Line 787. Use "... 90$^\circ$, is $\sim$4\% for ...".
 - Line 794. Use "... defined at first order if one ...".
 - Line 799. Use "... information from the present data, ...".
 - Line 803. Use "... evaluated for each 4-dimensional bin as".
 - Line 808. Use "For the BSA and the TSA, the corrections are on average ...".

Page 15.
 - Line 818. Use "... the quantities in the definition ...".
 - Line 823. Use "... uncertainty for each bin was computed as".
 - Line 825. Use "... $i$ out of $N$ variations ...".
 - Line 840. Use "statistical uncertainty".
 - Line 850. Use "... that was used ...".
 - Line 856. Use "... smaller than that from the ...".
 - Table IV caption.
   - Line 1. Use "... uncertainties relative to the asymmetry at 90$^\circ$ for each source of uncertainty and
       for each asymmetry type."
   - Line 3. Typo on "$P_bP_t$".
 - Line 868. Use "... statistical uncertainty is bigger than the total systematic uncertainty.".
 - Line 878. Use "... not affect the polarization ...".
 - Line 879. Use "... cross sections even up to the 20\% level.".
 - Line 883. Use "... is valid at CLAS kinematics ...".
 - Line 884. Use "... statistical uncertainties and ...".

Page 16.
 - Line 902. Use "... gluonic GPDs that are not ...".
 - Line 919. Use "... by fitting both deep inelastic scattering (DIS) ...".
 - Line 935. Use "... bin, $\beta$ was set to zero ...".
 - Line 937. Use "... with their uncertainties, ...".
 - Line 940. Use "... asymmetry as a function of $\phi$ for each slice ...".
 - Line 950. Use "... $-t$ for each $Q^2 ...".
 - Line 958. Use "... values, the VGG model ...".
 - Line 964. Use "... with respect to the $(x,\xi)$ dependence.".
 - Line 969. Use "... observed for larger ...".
 - Line 986. Use "... Fig. 20 as a function of $\phi$ for each ...".
 - Line 990. Use "... different in shape and ...".
 - Line 995. Use "... the data were fitted ...".
 - Line 997. Use "... $t$-dependence for each bin in $Q^2-x_B$ of the ..."

Page 17.
 - Fig. 18 caption.
   - Line 1. Use "... events as a function of $\phi$ for the ...".
   - Line 3. Use "... bin, $\beta$ was set to ...".
   - Line 3. You point out the highest t bin for Q2=2.41 GeV2 has limited coverage, but you have said nothing
      about the lowest t bin at Q2=3.31 GeV2 that has only a single data point (i.e. it has even more limited
      phi coverage). Any comment? The same question is applicable to the other plots of asymmetries.

Page 18.
 - Fig. 19 caption.
   - Line 1. Use "... t dependence for each $Q^2-x_B$ bin of the ...".
   - Line 8. Use "... green data come from the ...".
   - General point. The orange and the red colors are indistinguishable. This is also true for
     Figs. 20, 21, 23, 24, 25, and 26.
 - Line 1011. Use "... the electric charge ...".
 - Line 1012. Use "... devoted to the ...".
 - Line 1025. Use "... provide strong guidance to ...".
 - Line 1045. Use "... published data, and extend ...".
 - Line 1047. Use "... was made including in the fit ...".
 - Line 1053. Use "... HERMES Collaboration, ...".
 - Line 1064. Use "... verified by comparing ...".
 - Line 1067. Use "... the $\sin \phi$ term, often ...".
 - Line 1068. Use "... high $-t$ in some kinematic bins towards ..."
 - Line 1079. Use "... of $\phi$ for each bin ...".

Page 19.
 - Fig. 20 caption.
   - Line 1. Use "... events as a function of $\phi$ for the ...".
   - Line 2. Use "shaded bands."
   - Line 3. Use "... bin, $\beta$ was set to zero ...".

Page 20.
 - Fig. 21 caption.
   - Line 1. Use "$t$ dependence for each ... bin of the ...".
 - Fig. 22 caption.
   - Line 3. Use "... data integrated over ...".
   - Line 4. Use "... [14] (magenta triangles), ...".
   - Line 5. Use "... [13] (green squares).".
 - Line 1084. Use "The data were fitted ...".
 - Line 1088. Use "... bin in Figs. 24 ...".
 - Line 1095. Use "(green dot-dashed curve)".
 - Line 1109. Use "In recent years, ...".
 - Line 1110. Use "... procedures to extract the Compton ...".
 - Line 1112. Use "... [9,15] based on a local-fitting method at a given ...".
 - Line 1113. Use "... point, the CFFs ...".
 - Line 1126. Use "... parametrized in the VGG model by ...".

Page 21.
 - Fig. 23 caption.
   - Line 1. Use "... events as a function of $\phi$ for the ...".
   - Line 2. Use "shaded bands".
   - Line 3. Use "... bin, $\beta$ was set ...".

Page 22.
 - Fig. 24 caption.
   - Line 1. Use "$t$ dependence for each ... bin of the ...".
 - Line 1148. Use "... 1.97~GeV$^2$ ...".
 - Line 1154. Use "... [33] using the same fitting code with the results ...".
 - Fig. 25 caption.
   - Line 1. Use "$t$ dependence for each ... bin of the ...".
 - Line 1157. Use "... the much larger kinematic coverage of our data, ...".
 - Line 1172. Use "... statistical uncertainties. The ...".

Page 23.
 - Fig. 26 caption.
   - Line 1. Use "$t$ dependence for each ... bin of the ...".
   - Line 4. Use "... [12] integrated over all values of $Q^2$ at ...".
 - Line 1192. Use "M\"{u}ller".

Page 26.
 - Table V caption.
   - Line 1. Use "... three asymmetries with their statistical and systematic uncertainties for each ...".

References.
 - Put the references in the order cited in the paper.
 - The form of the references is consistent. In general it should be as follows:
   S. Niccolai {\it et al.}, Phys. Rev. Lett. {\bf 90}, 116 (2014).
 - Include the Collaboration names with the papers. For example:
   S. Niccolai {\it et al.} {\it (CLAS Collaboration)}, Phys. Rev. Lett. {\bf 90}, 116 (2014).
 - For papers with only two or three authors, include "and" before the last author. For example:
   A.V. Belitsky and A.V. Radyushkin, ...
 - List only the first page of the publication, not a page range.
 - Be consistent with your journal name abbreviations (see Ref. [19] for a problem).
 - Comma after journal volume, not semi-colon. See Ref.[29] for a problem.
 - Refs. [9] and [23] do not seem to be used in the paper. If so, eliminate them from the list.