[Clascomment] OPT-IN: Resolving the proton form factor problem by comparing electron and positron scattering from the proton

Tue Nov 18 15:17:29 EST 2014

Dear Dan,

Thank you for your gloriously thorough reading of the paper.  We have 
adopted most of your suggestions.

- Larry

Daniel Carman wrote:
> Larry et al.,
>
> I have read through the draft TPE paper dated November 14. 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
>
> ************************************************************************************
> Page 1.
> - Institution list. Use "Santa Maria".
Done
> - Abstract.
>    - Line 6. Use "liquid-hydrogen".
nope
>    - Line 8. Use "... simultaneously, as well ...".
done
>    - Line 9. Use "systematic uncertainties".
nope.  The errors cancel, leaving a smaller systematic uncertainty.
> - Missing PACS numbers.
added
> - Line 17. Use "... GeV$^2$ [1-9]".
done
> - Line 36. Use "... form factor extract $G_E$ from ..." (You introduced G_E as the electric form
>    factor and you now call it the charge form factor. This helps to improve clarity.)
done
> - Line 38. Use "... because the $G_E$-dependent part of the cross section is small compared to the
>    $G_M$-dependent part at large $Q^2$, ...".
done
> - Line 44. Use "... virtual photon. These corrections are therefore not ...".
done
> - Line 52. Use "... positron beams, existing older measurements of ...".
ok
> - Line 54. Use "However, two new experiments, ...".
too many howevers.
> - Line 58. Use "In this work, we used a unique ...".
ok
>
> Page 2.
> - Second line from top. Use "higher-order QED".
ok
> - Line 7. Use "... then used the photons ...".
ok
> - Line 9. Use "... (RL) gold foil to produce ...".
ok
> - Line 11. Use "... diverted by the Hall B tagger magnet [29] ...".
ok
> - Line 14. Use "... gold foil to produce ...".
ok
> - Line 20. Use "30-cm-long liquid-hydrogen".
nope
> - Line 22. Use "... line, see Ref. [28]".
ok
> - Line 32. Add ref. for CC (G. Adams et al., NIMA 465, 414 (2001).
we didn't use the CC so I'm only mentioning it for completeness
> - Line 35. The only system without an explanation of its purpose is the EC here. Use "... (EC) [33]
>    for electron/pion separation".
added 'for triggering' since that is what we used it for
> - Line 35. Use "The CLAS momentum resolution ...".
not needed.
> - Line 42. Use "A compact mini-torus magnet placed ...".
ok
> - Line 47. Use "... uncertainties between the $e^+p$ and $e^-p$ final states due to ...".
not sure that helps
> - Line 57. Problem with opening quotation on "left beam". Also, it is not clear what you mean by "left beam".
>    Please clarify.
added the phrase: `left beam' luminosity for particles passing on the 
left side of the chicane
> - Line 59. Problem with opening quotation on "ratio of ratios".
ok
> - Line 65. Use "... events for the difference chicane ($c$) ...".
ok
> - Line 66. Use "... polarity settings."
not needed
> - Line 84. "... thus matching the acceptances for electron and positron.". You wording is unclear to me.
>    You cannot match the acceptance for electrons and positions for a given field polarity configuration
>    given the different paths through the spectrometer. Please clarify what you are trying to say.
we matched the geometric acceptances
> - Line 88. Use "... incident lepton beam energy ...".
no, because the beam did not have a single energy.  Each incident lepton 
had its own energy.
> - Line 90. Use "Since elastic lepton-proton ..." (to cover both e+ and e- beams).
ok
>
> Page 3.
> - $E_l$ is not defined here.
defined on p2, l90
> - Add comma after $\Delta p_p$ equation.
ok
> - Line 7. Shouldn't this be "$\Delta E_l^{\pm}$?
It could be
> - Line 8. What is meant by "We identified positions and electrons kinematically."?
by whether their momenta and angles satisfied the elastic constraints.  
This is explained in the next sentence.
> - Fig. 1. Are the red and blue curves fits to the data? Why are you not showing histograms of the data?
those are the data.  Caption modified to make it clearer.
> - Line 27. Use "through CLAS and ...".
ok
> - Line 28. Use "... original lepton or oppositely charged .. malfunctioning counter.".
no.  we also threw out the event if the proton hit the counter
> - Line 40. Use "... polarity was identical ...".
ok
> - Line 46. "The negative chicane data for magnet cycle two were discarded ... TPECal were anomalous.". This
>    is a worrying statement to me that raises alarm bells. What specifically was the reason for the problem?
>    If you cannot say, how can you be 100% certain that this same problem didn't affect other settings are
>    a lower level and you are attributing to a TPE signature? I think that you need to consider your wording
>    here with some more care.
replaced 'anomalous' with 'very different from unity'
> - Line 46. "This effect also appeared ... cross section ratio." I cannot make sense of what you are trying
>    to say here for certain.
sentence deleted
> - Line 49. Use "... that had a uniform acceptance ...".
ok
> - Line 56. "The acceptance correction factors are all within 0.5% of unity ...". What are you trying to say?
>    Are you saying that the e+p and e-p acceptances in CLAS are 99.5%? Please clarify your point here.
No.  The ratio of e+p to e-p acceptances for positive torus times the 
same for negative torus were within 0.5% of unity.
> - Fig. 2 caption.
>    - Line 3. Use "GeV$^2$".
OK
>    - Line 4. Use "... 1.45~GeV$^2$ data.".
ok
>    - Remove the last sentence as it repeats exactly what is stated in the second sentence."
ok
> - Line 59. Use "Our TPE data ...".
ok
> - Line 60. Use "A small scattering angle $\theta$ corresponds to a virtual photon ... and a large ...".
fixed
>
> Page 4.
> - Second line from top of page. You have not said anything about your Q2 bins. What are your bin centroids
>    and extents?
not sure how to do this in the space available.  Perhaps we should put 
it into the supplemental material.
> - Line 4. Provide a reference for the peaking approximation.
ok
> - Line 13. Use "... vertex cuts was estimated as the difference ...".
> - Line 15. Use "... cuts was estimated as the difference ...".
> - Line 17. Use "... selection was estimated as the difference ...".
> - Line 32. Use "... was estimated to be ...".
too many extra words
> - Fig. 3. Are the model curves predictive or have any of the data shown (older data or this data) used to
>    provide constraints? That is not apparent from what is included here.
the model curves are predictive
> - Fig. 3. Provide references for "previous world's data".
will do
> - Right column first line. Use "... to a linear function in ...".
ok
> - Right column second line. What do you mean by a "reduced cross section"? Is this a ratio of e+p/e-p or
>    something else?
it's defined in the Andivahis paper.  Added 'electron scattering' before 
'cross section'
> - Line 61. Problem with opening quotation on "Unpolarized + TPE cross section".
ok
> - Line 64. Use "$e^+p/e^-p$.
ok
>
> Page 5.
> - Fig. 4 caption. You need units of GeV^2 on the Q2 denominator of G_D^2.
ok
> - Fourth line from top of page. Use "... measurements. At ...".
ok
> - Line 10. "However, those calculations are not quite large enough to resolve the discrepancy at higher
>    $Q^2 [14,34]." Are you saying that at higher Q^2 that TPE effects are not sufficient to resolve the
>    discrepancy between polarized and unpolarized data? Are you saying that the calculations are not fully
>    trustworthy at higher Q^2? Maybe you are saying something else?
The TPE effects as calculated from these calculations are not sufficient.
> - Line 18. Use "... of TPE effects and examine ...".
ok
> - Ref. [25]. Do not include arXiv number for published work.
ok
> - Ref. [34]. Use "... Yang, arXiv:1407.2711, (2014).".
That is the results of bibtex.  I'll let the PRL copy editor fix all that.
> - Ref. [35]. Use "... Collaboration), arXiv:1303.2160, (2013).".
> - References: "et al." should be in italics font everywhere.
> - Ref. [28] should include "(CLAS Collaboration)" after et al.
ok
> - Your data should be included in the CLAS physics database and that reference should be included in this
>    reference list.
I'll ask Dasuni to enter the data in the CLAS physics data base.
> - You mention in the paper about "supplementary material". What do you mean by this?
It's posted on the reviews page and should have been circulated.  It 
consists of (a) data tables and (b) tables of uncertainties.

-- 
				Sincerely,
				Larry

-----------------------------------------------------------
Lawrence Weinstein
University Professor
Physics Department
Old Dominion University
Norfolk, VA 23529
757 683 5803
757 683 3038 (fax)
weinstein at odu.edu
http://www.lions.odu.edu/~lweinste/