[Halld_src] [EXTERNAL] SRC-CT J/ψ Manuscript

[Axel Schmidt]

Regarding the supplement:

- Can you give an explanation of what the chi parameter "means" in eq. 3?

- Is there any rationale for the values of the modification coefficients 'a' (eq. 8) and 'b' (eq. 9)?

- I would add to the caption of Fig. 4 that this is simulation. (I know it should be obvious, but help avoid misconceptions)

- I am embarrassed that I cannot recall the rationale for when you average just helium and carbon, and when you average deuterium, helium, and carbon all together. Can you walk me through that again?


Thanks for this comprehensive work, Jackson!
-Axel
________________

> On Jul 1, 2024, at 12:01, Axel Schmidt <axelschmidt at gwu.edu> wrote:
> 
> Dear Jackson, 
> 	I have read the paper (will read the supplement now) and I have some comments which I hope are helpful. Please feel free to disregard any that you disagree with. 
> Best,
> Axel
> ________________
> 
> Abstract
> 
> "above and below the threshold energy..."
> --> I think we should clarify that this is the threshold energy for photoproduction from a free nucleon.
> 
> 
> Introduction
> 
> "Understanding the partonic structure of nuclei" is technically not a question.
> It is a task, an undertaking, a goal, but it's not a question. A question would be: "How is nuclear structure determined from fundamental quarks and gluons?"
> I'm also not crazy about the word 'outstanding,' but I'll live. I'd prefer 'major' or 'primary' for reasons that some progress has been made. It's a question of degrees. We'd like to understand better than we do, but we do already understand a lot. 
> 
> 
> "The photoproduction of J/ψ particles off nucleons is mediated primarily by the exchange of gluons, and is therefore directly sensitive to the gluon density inside nucleons."
> Just note that this is not a universally held truth. Craig Roberts would disagree with that statement. His scalar di-quark model seems to dispute gluon exchange mechanism, but I am far from understanding exactly what the reaction becomes sensitive to.
> 
> 
> "Measuring only the inclusive production of J/ψ, they cannot provide direct knowledge of the incident photon energy."
> Inclusive, to me, doesn't necessarily imply 'untagged.' I think we need to specify that the previous measurements did not have a mechanism for tagging photon energy, AND because they were inclusive, they couldn't back this out by other means.
> 
> 
> "therefore observing no J/psi events."
> The word "therefore" does not sound appropriate to me. It would have been possible for them to have observed events (which is why they did the search).
> 
> 
> "The detection of a knocked-out proton allows both an improved reconstruction of the dilepton invariant mass and an inference of the initial-state nucleon momentum"
> I would prefer "The detection of a coincident proton" to "knocked-out" so we don't imply any speculation about the reaction mechanism.
> 
> 
> "We observe a small but significant number..."
> All well and good, but would you feel comfortable putting a number of sigma in parentheses after "significant" as in, "significant (X sigma)"?
> Have we estimated the significance of the subthreshold J/psi signal over the background only hypothesis? Since you already know the mass of the particle, this should be easy to do. 
> 
> 
> Experiment
> 
> "via coherent bremsstrahlung from a diamond radiator."
> IMO, we should cite the GlueX NIM here as well, since that is the reference that covers the beamline.
> 
> I'd prefer "The energy COMMA E_\gamma COMMMA of the bremsstrahlung..."
> 
> Instead of "with a primary coherent enhancement at an energy 7.6-8.6 GeV."
> I'd prefer "with additional coherent enhancements, the primary enhancement occuring at an energy of 7.6–8.6 GeV. 
> 
> "using two calorimetry method following Ref. [12, 14]"
> Something is not right here.
> "using two calorimetry methods, following Refs. [12, 14]" 
> or
> "using A two-calorimeter method, following Refs. [12, 14]
> or
> "using THE two-calorimeter method, following Refs. [12, 14]"
> 
> "Identification of the proton..."
> 	I feel like this should be a new paragraph, even if one sentence long. If you want to make two sentences, you could do:
> "Identification of the proton in the reaction was performed by comparing track momentum with time of flight signals provided by either by the FCAL, BCAL, or TOF. Additional discrimination was achieved by considering energy loss in the SC, CDC, and FDC."
> 
> "tagged beam bunch RF time"
> 	RF is not defined. Nor is it particularly meaningful. 
> "if the signal in the tagger fell within a 2 ns window synchronous with the arrival of the photon at the target."
> 
> "to account for the substantial rate of accidental photons in the tagger"
> Technically, photons do not go to the tagger. I suggest:
> "The substantial background caused by accidental coincident tagged photons was estimated and subtracted by using the rate of "off-time photons" with tagger signals between 6 and 18 ns before or after the synchronous time." 
> You can add "event mixing" in if you like, but that is a complication that I feel can be safely left to the supplement.
> 
> "To improve on this..."
> I think we can make this sentence more clear by setting off the mathematical definitions in commas.
> "To improv on this, we make the observation that, along with the transverse momentum COMMA p_\perp COMMA, the light-cone coordinate "minus" component of the momentum COMMA p^- \equiv E - p_z COMMA is well (no hyphen) reconstructed for the high-momentum leptons..."
> 
> "is the total momentum of the measured final-state."
> --> "is the total four-momentum of the measured final-state."
> 
> "for mean-field protons"
> I worry that this expression will not be clear to a general PRL audience. Would "low momentum" be better? Or perhaps "protons in mean-field states"?
> 
> "and reconstructed as measured data."
> This has the unfortunately implication that the Geant4 data becomes measured data.
> I suggest, "and reconstructed in the same manner as the measured data."
> 
> "the simulation extracted efficiency was rescaled by a factor..."
> This is one place where the passive voice construction really makes things hard to follow.
> What we want to say is that our simulation over-estimates the true efficiency, and so we presume a true efficiency is actually 84.7% of what we got with simulation. 
> "Following a recent study of the QED Bethe-Heitler process with GlueX [37] that found the experimental e+e- efficiency to be 84.7 ± 1.9% of that predicted by simulation, we rescaled our simulated efficiency results by that factor to arrive at estimated efficency of ≈11%."
> 
> 
> Results
> 
> 
> Fig. 2: Remind me again why deuterium is not included in the average?
> 
> Fig. 3: Is this for all three nuclei (as shown in Fig. 1), or for C+He (Fig. 2)?
> 
> In the abstract, you talk about measurements of the differential cross section as a function of momentum transfer, but you don't show them in the paper. I think a sentence pointing the reader to the supplement would be appropriate. 
> 
> 
>> On Jun 25, 2024, at 00:04, Jackson Reeves Pybus via halld_src <halld_src at jlab.org> wrote:
>> 
>> Hello SRC-CT group members.
>> 
>> As discussed in this morning’s meeting, given the wrap-up of the internal J/ψ analysis review, I am emailing to distribute the draft of the manuscript “First Measurement of Near- and Sub-Threshold J/ψ Photoproduction off Nuclei” (along with the supplemental material for the paper). Comments and questions regarding the analysis and the manuscript are appreciated and should be sent to me at (jrpybus at mit.edu <mailto:jrpybus at mit.edu>).
>> 
>> In addition, here is the google-form signup link for authorship to the paper, so please sign up now to be included as an author on the final paper:
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__docs.google.com_forms_d_e_1FAIpQLScx4u2554oJ7Go6Qgg9-5FgWqivcNkVfMhSAE2AGeUp-2DT-5FO7xVw_viewform-3Fusp-3Dsf-5Flink&d=DwIFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=66Sb4pp0d4diwFuNQ_jTiKyZDsB_FG2X3Hlmk9_wuSY&m=E-fT4FOTEF7TS75HUJewK2_a92uBbe-5tJhIaI2aA9CthWXS63oiVMHNjtVbZk_0&s=poJoIoBXQakMf7k4aaJ262VMK88D7Awpf_URUpt4eG0&e= 
>> 
>> Comments on this draft would be appreciated by the end of this week, Friday, June 29.
>> 
>> Best regards,
>> Jackson Pybus
>> 
>> <SRC_CT_JPsi_Paper_v1.pdf>
>> <SRC_CT_JPsi_Supplement_v1.pdf>
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> 

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