[Clascomment] OPT-IN: Measurement of Unpolarized Cross Sections and Polarized Cross Section Differences for Deeply Virtual Compton Scattering
Daniel Carman
carman at jlab.org
Tue Aug 1 16:31:28 EDT 2017
Dear Nicholas et al:
I have read through your draft paper on the DVCS cross sections from
the e1-dvcs2 experiment and include my comments below. In general,
while the data are quite nice, the paper reads more like a rough draft
throughout and I am quite disappointed that this has made it through an
ad hoc review in its current state. Many aspects of this draft need
improvement before it will be ready for submission. I have tried to capture
what I could in my comments below, but I would appreciate an updated draft
to review after my comments are considered in full.
Regards,
Daniel
-----------------------------------------------------------------------------
General:
- Throughout the draft you typically describe things using the present
verb tense when you should be using the past. I have tried to capture
these in my comments below.
Page 1:
- Title: What a mouthful! Please remove the listing of the kinematic
ranges in this title. I suggest "Measurements of Unpolarized and
Polarized DVCS Cross Sections with CLAS".
- Abstract.
- Line 1. Use "deeply virtual Compton scattering" to be consistent
with your usage elsewhere.
- Line 4. Typo on "unpolarized".
- Line 7. Use "generalized parton distributions" to be consistent
with your usage elsewhere.
- Left column.
- Line 44. Use "(TMDs)".
- Line 48. Use "... description of the nucleon in terms ...".
- Right column.
- Line 51. Use "... $ep \to e'N'M'$. These processes describe the
nucleon in terms of the longitudinal ...".
- Line 61. Use "... "hard" part, which consists of ...".
Page 2:
- Left column.
- Line 93. Use "... unpolarized GPDs, whereas ...".
- Line 97. Use "... limits that are ...".
- Line 112. Use "... b_\perp)$, which provides ...".
- Line 116. Define DIS.
- Line 123. Typo on "cannot".
- Right column.
- Line 137. Use "... also receive a contribution ...".
- Line 152. Do not indent this line.
- Line 156. Use "... is much larger, except near ...". Also $\phi$
here is not defined.
- Line 158. Use "... mainly gives access ...".
- Line 163. Use "... DVCS amplitude, which is ...".
- Line 166. Use "... including those at Hall~A ...".
Page 3:
- Left column.
- Fig. 2: Indicate the scale on the figure or in the caption.
- Line 182. Use "... detector was based ...".
- Line 183. Use "... coils were placed ... the beamline.".
- Line 186. Use "... particles was accomplished ...".
- Line 189. Use "... (EC) were responsible ...".
- Line 190. Use "... EC was also responsible ...".
- Line 194. Use "... ran from October 2008 to January 2009, ...".
- Line 196. Use "... run time, with a ... $4.5 \times 10^7$/nb ...".
- Line 199. Use "... at 20~K ... upstream relative to ...".
- Line 201. Use "... CLAS detector package, ...".
- Line 202. Use "... (IC) (Fig. 3), ...".
- Line 203. Use "... place at the center of CLAS."
- Right column.
- Fig. 3 caption. Line 1. Use "Magnification of the CLAS target ...".
- Fig. 4. The figure is poor quality (grainy). Also you label the angle $\phi$ in
the figure but switch back and forth between $\phi$ and $\phi_\gamma$ in the text.
Choose a convention and stick with it.
- Line 206. Typo on "equipped".
- Line 207. Use "... solenoid assisted in sweeping the M{\"o}ller background created
during electron beam interactions in the target into the beam pipe.".
- Line 217. Use "... E'}$, where $E$ is the ...".
- Line 219. Use "... energy; $t$ is the ...".
- Line 225. Use "... additional cut to remove events with $W < 2$~GeV ...".
Page 4:
- Left column.
- Fig. 5 caption.
- Line 1. Use "The $Q^2$ vs. $x_B$ kinematical domain for e1-dvcs2 after all cuts."
- Line 236. Use "... completed filled because of various cuts that we detail ...".
- Right column.
- Line 263. Use "... area that was not ...".
- Line 265. Use "... sections varied rapidly in this region.".
- Line 273. Use "... we identified the three ...".
- Line 274. Use "... we accepted every event that has ...".
- Line 278. Use "... electrons required a hit in the same sector of CLAS in ...".
- Line 279. Use "... (which formed the trigger) and EC with a momentum greater than ...".
- Line 281. Use "... trigger suppressed pions ...".
- Line 283. Use "... Since the electrons lost all of their energy ...".
- Line 284. Use "... they deposited an energy ...".
- Line 287. Use "... in the EC and $p$ is the momentum as measured ...".
- Line 289. Use "... field. More massive ...".
- Line 291. Use "... ionization, therefore a ...".
- Line 293. Use "... indicated which particles were electron ...".
- Line 294. Use "... proportional to their momentum ...".
- Line 299. Use "... The final cut required that a particle had ...".
Page 5:
- Left column.
- Line 300. Use "... fraction that lies within ...".
- Fig. 6. z-axis labels overlap color bar. y-axis label overlaps axis values.
- Fig. 6 caption. Line 4. Use "... is visible at $f_s = 0.12$, which lies outside ...".
- Line 302. Use "Additionally, fiducial cuts were applied to avoid areas where the
geometrical acceptance of CLAS was small and changing rapidly.".
- Eq.(5). Use "$\Delta \beta = \beta_{TOF} - \beta_{DC}$".
- Line 312. Use "... peak about $\beta = 0$ does not significantly ...".
- Line 313. Use "... horizontal cut was taken.".
- Line 314. Use "... for this analysis was ...".
- Line 317. Use "... identification include geometrical fiducial cuts ...".
- Line 320. Use "Two detectors in this experiment were used to ...".
- Line 321. Use "The first was the EC for lab scattering angles ...".
- Right column.
- Fig. 7 caption. Line 1. Use "The proton identification cut on ... momentum $p$".
- Line 322. Use "... 20^\circ$ and the second was the IC for ...".
- Line 324. Use "... in the EC was achieved ...".
- Line 329. Use "... in the EC relative to the reference ...".
- Line 331. Use "... from the center of CLAS to ...".
- Line 332. Use "... vector from the center of CLAS ...".
- Line 333. Use "... electron that was detected ...".
- Line 335. Use "... peak about $\beta = 1$, ...".
- Line 336. Use "... a tail to lower $\beta$, representing the neutrons.".
- Line 337. Use "The final photon selection cut requires $\beta > 0.9$ (see Fig. 8)."
- Line 340. Use "It was assumed that .. in the IC was from a ...".
- Line 341. Use "... electrons was removed by the analysis cuts."
- Line 344. Use "Several corrections to the measured ...".
- After line 349. Add "Details regarding these corrections are provided in the following
subsections.".
Page 6:
- Left column.
- Line 351. Use "... loss as occurring ...".
- Line 354. Use "... This code simulated ...".
- Line 356. Use "... of traversing particles as described in ...".
- Line 357. Use "... were generated within the target with momentum ...".
- Line 359. Use "... through the detector taking into account ...".
- Line 360. Use "... response to yield the reconstructed ...".
- Line 362. Use "The energy loss corrections were given by the difference ...".
- Line 363. Use "... sets of momentum values,"
- Line 367. Use "... then applied to the reconstructed momenta.
- Note: Make a statement as to the size of the momentum corrections.
- Line 370. Use "... beyond energy loss, for ...".
- Line 371. Use "... misalignments or ...".
- Line 374. Use "... distributions and our ...".
- Line 375. Use "... of the energy loss corrections, ...".
- Line 376. Use "... them to the expected ...".
- Line 377. Use "... 5.88~GeV for the elastic channel.".
- Right column.
- Line 384. Use "... on the electron kinematics.".
- Line 392. Use "... general, was different from ...".
- Line 394. Use "... by determining:".
- Eq.(11). End equation with a period for proper punctuation.
- Line 395. Typo on "dependence".
- Eq.(14). Denomination should be sin^2(the/2) not sin (the/2)^2.
- Line 404. Use "... was due to the corresponding ...".
Page 7:
- Left column.
- Line 409. Use "... particles that minimizes ...".
- Line 411. Use "... according to:"
- Line 420. Note: I think that you should show before/after results and discuss
the improvements in resolutions and centroids.
- Line 423. Use "... First, we demanded ...".
- Line 426. Use "... laws - our so-called ...".
- Line 432. Why the unnecessary column shifting here?
- Line 469. Use "The CLAS detector was not 100\% efficient in recording events due
to acceptance losses due to gaps between the sectors associated with the torus
coils and the inefficiencies associated with the edges of the different detector
subsystems. In order to obtain a cross section ...".
- Question: How have you accounted for system dead time, trigger inefficiencies, and
tracking inefficiencies?
- Line 473. Use "... events that were missed by the detector to determine the acceptance".
- Line 475. Use "... events that were detected ...".
- Note: Your discussion here focuses (really) only on the geometrical acceptance. How
have you accounted for inefficiencies?
- Right column.
- Line 440. Use "... and the measured angle,".
- Line 442. Use "... photon, and the recoil proton."
- Line 443. Use "Each of these variables should be centered about zero. However, due to
resolution effects, ...".
- Line 447. Use "... choosing the exclusivity ...".
- Line 448. Use "... (Figs. 9, 10, 11, and 12)".
- Line 450. Remove period at the end of this line.
- Line 452. Use "... (Figs. 13, 14, 15, and 16).".
- Note: You reference Figs. 9 to 16 here but you have not discussed them in the text.
- Line 457. Use "... applied cuts that decreased the background. These cuts were ...".
- Line 466. Add a period at the end of the sentence.
- Note: The MC do not compare so well to the data looking at Figs. 9 to 16. You need to
discuss these figures and what the obvious differences mean and how they either do
or do not affect your results and systematic uncertainty assignments.
- Line 482. Use "... of the detector geometry ..."
Page 8:
- Figs. 9, 10, 11, 12, 13, 14, 15, 16. These figures are not well put together. The UL
and LR plots are not labeled, the cut and paste color scale is not acceptable, and the
wasted space with the label box should go. I suggest that you convert these figures to
a 2 x 3 grid, with the top 3 subplots the MC distributions and the bottom 3 subplots the
corresponding data distributions, thus reducing the 8 figures to 4 figures.
- Fig. captions for Figs. 9, 10, 11, 12, 13, 14, 15, 16. The captions all have the same
issue. Use "... after preliminary cuts and with fits:".
- Left column.
- Line 490. Use "... software that reproduce the measured detector resolutions.".
- Line 500. Use "An ensemble of events ...".
- Line 502. What do you mean by "both virtual and radiative effects"? You need to be
more precise in your language and provide some relevant details for the reader.
- Right column.
- Line 514. Use "The EC was not perfectly ...".
- Line 515. Use "... showering that occurred within ..."
- Line 519. Use "... perfectly in the simulations.".
- Line 521. Use "... CC was not perfectly ...".
- Line 523. Use "... effects that were not taken into account in the simulations.".
- Line 525. Use "... simulations was too narrow in comparison to the actual data.".
- Line 528. Use "... called GPP (for GSIM post-processor).".
Page 9:
- Left column.
- Line 529. Use "GSIM Post-Processor"
- Line 530. Use "There were imperfections in the detector that were not included in
GSIM.".
- Line 533. Use "... a post-processor called GPP was employed. DC sense wires that had ...".
- Line 535. Use "... in the experiment were ...".
- Line 536. Use "... from the simulations.".
- Line 537. Use "... in the experiment ... wires in the simulation ...".
- Note: The GPP section is not complete. GPP serves two main purposes. The first is
to knock out bad channels, the second is to smear the DC and TOF timing so that the
MM resolutions of the MC and the data match.
- Line 540. Use "During the experiment there was ...".
- Line 541. Use "... scattering or other accidental events being ...".
- Line 543. Use "... cosmic rays, or other random ...".
- Line 545. Use "... way. This background was linearly ...".
- Line 548. Use "... background was not taken ...".
- Right column.
- Line 551. Use "... background in the data.".
- Line 551. There is no such thing as a "Faraday cup trigger". Also, what do you mean
that the Faraday cup records the "state of CLAS". The Faraday cup is a charge
integrator. Your language needs to be made more precise here.
- Line 555. Use "... rate that we measured ...".
- Note: I do not find this "Background Merging" section particularly well written. Please
review for clarity and accuracy.
Page 10:
- Left column.
- Line 570. Use "... was made to correct the bin yields.".
- Line 572. Use "... the $\pi^0$ could decay ... photons were detected.".
- Line 573. Use "... \gamma + \gamma$. Second, the $\pi^0$ could decay such that
only one photon was detected and the other is missed, either due to acceptance
effects or the 150~MeV photon detection threshold of the calorimeters. We
refer to this as $\pi^0 \to \gamma + (\gamma)$, with the ... not detected."
I would delete the remainder of this paragraph as it is not necessary.
- Line 579. Use "... energy could be so low
- Right column.
- Line 602. Use "... detected was determined.".
Page 11:
- Left column.
- Line 609. Use "... are denoted as ...".
- Line 615. Use "... of the photon pair ...".
- Line 621. Use "$E_X$, the missing energy ...".
- Line 624. You have changed notation in using $MM_{e'X\gamma_1\gamma_2}^2$. I
also think the MM and IM notation with the "+" signs including between the
different particles cumbersome. I suggest that you use, e.g. $"IM_{\gamma_1 \gamma_2}$,
etc.
- Right column.
- Line 631. This line should not begin a new paragraph.
- Line 632. Remove the sentence "We took a cut at the three sigma level." You have already
stated on line 625 your cut limits.
- Line 635. The statement "The ratio of pion to single photon background ..." is unclear.
- Line 639. Use "... 310$^\circ$ and $\vert t \vert$ near 0.1~GeV$^2$, where the yield is
maximal, it is typically ...".
- Line 640. Use "... near 180$^\circ$ and ... near 0.5~GeV$^2$ where the yield is minimal,
it ...".
- Line 642. Use "The measured cross ...".
- Line 645. Use "... can be calculated and used to ...".
- Line 646. Use "... Born cross sections. The virtual photon corrections ...".
- Line 647. Use "... vertex) and the real photon corrections ...".
Page 12:
- Fig. 13. The x-axis values for the LL plot all overlap.
- Left column.
- Line 648. Use "... cross sections in ...".
- Line 649. Use "... interfere coherently, while the latter interfere ...".
- Line 650. Use "... experiment, each of these ...".
- Line 652. Use "... virtual photon corrections ...".
- Line 658. Use "... and DVCS calculations. This ...".
- Line 660. Use "... without the soft ...".
- Note: Are your systematic uncertainties independent of kinematics or are you
presenting average values. Make this clear.
- Line 667. Use "... Examples of the radiative corrections as a function of ...".
- Line 668. End the sentence with a period.
- Right column.
- Line 670. Use "... analysis using CLAS ...".
- Line 671. Use "... is the determination of the overall normalization of ...".
- Line 672. Use "... results. For this analysis, this normalization procedure was ...".
- Line 672. The word "belief" sounds like some sort of faith-based analysis. This is
not a proper scientific statement. Please rewrite.
- Line 675. Take care with your statement "It is assumed ...". Your analysis should not
be based on untested assumptions. Please review this statement so the reader is not
left with a false impression.
- Line 677. Use "... of the overall ...".
- Line 678. Use "... normalization, we have made a ...".
- Line 680. Use "... quantity that has previously been measured [14,19].".
- Line 681. Use "Our measurement of the elastic cross section using CLAS ...".
- Line 683. Begin a new paragraph with "The elastic cross section ...".
- Line 687. Notation change. Use "$ep \to e'p'$". Did you detect both the electron and
the proton? More details are needed to clarify exactly what you did.
Page 13:
- Left column.
- Line 690. Use "... is shown in Fig. 20.".
- Line 702. Use "The major sources of systematic uncertainty ...".
- After line 707. Add "The estimated contributions from each of these sources is
detailed in the following subsections. Put the subsequent subsections in the order
in which they are listed as bullets.
- Right column.
- Line 698. The sentence "Note well that the ..." is far from clear. Are you making
sector-dependent corrections are not? (Note spelling of the word "dependent".)
- Eq.(22) gives a value of 4\% so you arbitrary change this to 5\% "to be conservative".
This change is not justified. If your approach that gives 4\% is not trustworthy,
then change your approach, don't just arbitrary increase your uncertainty, especially
as you have not done this for your other sources.
- Note: The elastic normalization does not provide any information on your acceptance
for photons, thus your adjustment of the normalization and your understanding of the
systematics is not complete. I think that you need to provide an estimate for the
normalization effects for your photons in both the EC and IC. Whether this is a change
in your normalization or another source of systematic uncertainty remains to be seen.
Page 14:
- Left column.
- Line 718. Use "... each of the exclusive ...".
- Line 719. Use "... \theta_{\gamma,X}$, and ...".
- Line 724. The final paragraph "The variation was in steps ..." is far from clear,
especially the par of how you define your systematic uncertainty. Please review
for clarity.
- Line 733. Use "... for the exclusivity cuts.".
- Right column.
- Line 737. The sentence "The procedure not only allowed us ..." is completely meaningless
to me. Please review for clarity.
- Line 747. Use "... statistical uncertainty."
- Note: What is the systematic from the model dependence of your generator. Your generator
is not discussed in this paper.
- Line 755. Use "... of 10.3\%. We find ...".
- Line 757. Use "... statistical uncertainty ...".
Page 15:
- Left column.
- Table II. Adding 5 and 5.5 and 4.2 and 3 in quadrature does not give 10.3!
- Table II caption. Use "Summary of systematic uncertainties of the cross section
measurements presented in this work.". Again, are these average values or do
you apply them a an overall scale uncertainty to data points. (I hope this is
not the case!)
- Why is there no mention of beam polarization related systematics in your section on
systematics?
- Line 761. Use "The cross sections were ...".
- Line 763. Use "... to determine the unpolarized ...".
- Right column.
- Line 769. Use "... 21, 22, and 23.".
- Line 778. Use "... 24, 25, and 26."
- Sections A and B. You have given only the most cursory statements regarding your
results here. I think some more work is necessary in describing your results across
your full kinematic phase space.
- Note: All cross sections from this work must be entered into the CLAS physics database
and a reference to the database provided in your text.
Page 16:
- Left column.
- Fig. 17 caption. Use "Data (top) and Monte Carlo ...".
- Fig. 18. Use black y-axis labels. Also, the labels are too small and this plot is
of poor/grainy quality.
- Right column.
- Fig. 19 overlaps the equation. Also for some reason you equations have ceased to be
labeled. All equations should be labeled.
- Fig. 19 the axis labels overlap the values.
- Fig. 19 caption. Use "Examples of the radiative correction factor as a function of
$\phi_\gamma$ for two representative kinematic bins.".
- Line 780. Use "... where $P$ corresponds to ...".
- Line 783. Use "... uncertainty of 3\% ...".
- Line 785. Use "... polarization was ...".
- Equations N+,0 and N-,0. These terms are not in the cross section at the top of the
column. Please fix your notation.
- Line 790. Use "... form factors and CFFs.".
- Line 791. Use "... twist-two as:".
- Equation for cross section. Goes into right margin.
- Line 792. There is no f1 term in the equation. There is an f4 term.
- Line 796. Use "... beam spin only at the ...".
- Line 797. Use "... twist-three level.".
Page 17:
- Fig. 20.
- Improve the y-axis label on the left plot.
- Plots are of poor/grainy quality.
- The horizontal line fit is not justified by the data. Fit with a line with the
Q2-dependent slope a fit parameter. This is a short coming in this work.
- Caption. Line 2. Use " ... Ref.[19] is shown as the red line.".
- Section XII. I find this section quite poorly written and incomplete. You need to
provide more details regarding e1-dvcs1 and take the scale differences seriously.
Even though the kinematic bins are not perfectly matched there is clearly a ~10%
normalization difference that you cannot avoid. It must be addressed here. Also
Fig. 27 is not a well-crafted figure. It is very sloppily made and presented.
- Line 804. Use "... recently been published ...".
- Line 808. Use "... of the experiments.".
- Line 812. The sentence "However, as the kinematics do not vary extremely ..." is
essentially content free. Please review.
- Line 816. The sentence "Additionally, a correction has been applied ..." needs more
explanation.
- Line 824. Use "This model parametrizes the GPDs ...".
- Line 826. Use "... parameters that are fitted to nucleon ...".
- Right column.
- Line 834. Use "... cross sections extracted ...".
- Line 843. Use "... intermediate, and ...".
- Line 847. Notation change. Use "$ep \to e'p'\gamma$".
- Line 852. Use "... sections, which peak at $\phi \sim 0$ are dominated ...".
Page 18:
- Figs. 21, 22, 23.
- Are these cross sections plotted at the middle of the bin or are they bin-centered
or bin-averaged. Please make a definitive statement in the text.
- There are no grey bands on any of these plots.
- Caption.
- Line 1. Give the kinematic values in the caption and not just on the plot.
- Line 1. Use "The black points represent ...".
- Line 2. Use "The blue (upper) curves are the results of the VGG model. The
red (lower) curves are from BH contributions only.".
- Left column.
- Line 864. The statement "is in the ball park of the data" is not appropriate for a
scientific paper. Please revisit your language.
- Line 868. Use "... to the H GPD ...". Also fix the style of "H" here.
- Line 869. Use "... differences, the largest ...".
- Right column.
- Line 875. The last bit "These studies, utilizing ..." is not a complete thought. Please
review your language.
Page 19:
- Left column.
- Line 877. Use "Summary and Conclusions"
- Line 880. Use "... with CLAS in a wide range ...".
- Line 882. I suggest to present the relevant range for your statistical and
systematic uncertainties.
- Line 883. Use "... supplement past JLab data ...".
- Line 884. Use "We have presented a comparison ...".
- Right column.
- Line 886. Use "... have compared the new results with the DVCS ...".
- Line 889. Use "... are currently active ...".
- Note: It seems to me that you have completely run out of steam at this point. This
final section is really a very weak section to end on. It really needs to be
revisited to make it complete and with a much more complete review of what has been
presented in this paper and some stronger statements regarding the usefulness of
these data must be spelled out.
References:
- You have a consistent style problem with your references. Do not put a comma between
the journal name and the journal volume.
- Do not include preprint numbers for already published papers.
- Ref.[10]. Include proper spacing in the Erratum reference.
- Ref.[15]. This is not a complete reference. Make it a CLAS-Note and provide a proper
URL.
- Ref.[16]. This is not an appropriate reference for a journal article. It is a sketchy
wikipage is not even viewable by the outside world.
Page 24:
- Table II.
- Your top table lists x_B and the, but Fig. 5 shows x_B and Q2.
- Add units for the t binning table.
- Add units for the phi binning table.
Page 25:
- Fig. 27 caption.
- Line 1. Use "... e1-dvcs2 for ...".
- Line 2. Use "... 1, 5, and 15, ...".
- Line 4. Use "... not exactly the same.".
More information about the Clascomment
mailing list