[Rgc_analysis] [EXTERNAL] Re: Comments on J12-24-RunGroupC

[Kuhn, Sebastian E.]

Dear all,

I am planning to submit the following in response to our reader. Please let me know if you want me to change anything. I will send this out tomorrow!

- Sebastian

————— 

Dear Krešimir,

thank you for your comments. I am providing my responses to each of the points you raised below. Please let me know if you have additional questions.

With best regards - Sebastian 

> On Jun 27, 2024, at 6:44 AM, Krešimir Kumerički <kkumer at phy.hr> wrote:
> 
> EXTERNAL to ODU: This email is not from an ODU account. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> Dear Sebastian,
> 
> I am a member of the PAC52 assigned to do a first reading
> of Run Group C Jeopardy update,
> (for which you are the contact person),
> 
> 
> Since this run group comprises some well-established
> and thoroughly reviewed experiments I don't have  many
> scientific questions.
> 
> Still, PAC has to address some points during Jeopardy review,
> and it would be helpful if you had some comments on the following:
> 
> 1. Jeopardy instructions say that "If the experiment has already received a
> portion of its allocated beam time, the spokespersons should present the status
> of the analysis of the existing data and the projected results for the final
> complete data set. The goal is to show the physics impact of the beam time
> requested in the jeopardy update."
> 
> I notice that update document focuses on the preliminary results from the
> already recorded data (actually small part of it), and I don't see any
> projections for the complete data set. This would be singularly
> helpful to have, but I certainly understand that this
> means a lot of work and likely cannot be produced for the PAC meeting. In that
> case, PAC will work with what we have.

As you know, analyzing data from such a complex apparatus as CLAS12 is a time-consuming process, and we are presently in the middle of converting the huge data set we collected in 2022-23 to meaningful physics observables. We have made considerable progress even since the submission of the update document, and in our oral presentation will be showing results based on the entire Summer 2022 part of the run (roughly 1/4 of the total accumulated statistics in terms of electrons on target). Furthermore, we will demonstrate (at least for some of the approved channels) what statistical precision we expect with the full 2022-23 data set, and how this would improve with the additional data from the remaining 40 PAC days.
I should add that, beyond increasing the statistical precision of the data, there are other advantages if we can take additional data. For instance, we had planned to minimize systematic uncertainties by taking data with two opposite torus polarities, and two opposite solenoid polarities. Some of these runs, as well as the full statistics on some auxiliary targets, had to be abandoned due to the solenoid power supply failure and other losses of beamtime.
> 
> 2. Is there any change in the status of the collaboration in terms of
> institutes, committed staff, and prospective students that could
> impact the feasibility of performing and analyzing proposed measurements?
> 
All spokespersons and other senior personnel are committed to setting up and taking data for the anticipated additional run of RG-C, and to analyze the complete data set including these new data. While some students working on the first run of RG-C will graduate (or have already done so) before RG-C can run again, we are actively (and successfully) recruiting new students (and postdocs) to work on the present analysis who will also help with the next run. By the time the new data are avaiilable, all analysis tools, simulations, and other procedures will be in place, and adding additional statistics to each of the channels under investigation should be fairly quick and straightforward.

> 3. Finally, I do have one "scientific" question. TAC report says that
> your APOLLO target "has been operating with great success". On the
> other hand, you mention problems with pre-irradiation of this target
> and consequently the sub-optimal polarization in the first part of
> your run, so the remaining 1/3 of the originally requested 120 PAC
> days, if approved, would result in more than 1/3 of the additional
> statistics. Could this improvement (or previous degradation) be somehow
> roughly quantified in terms of some effective PAC days or related quantifier?

I should clarify that the polarized target APPARATUS (i.e., all of the hardware and software that are part of operating “APOLLO”) has indeed worked nearly flawlessly. The comment about the less-than-optimal polarization refers to the target SAMPLES (material) which is pre-irradiated ammonia or deuterated ammonia. These samples (in particular the ND3 ones - your comment below is correct) started out with rather low polarizability, and had to be irradiated in situ (which is not an efficient use of beam time). Having a dedicated target material irradiation facility at Jefferson Lab AND a setup to check the polarizability of the target material before inserting it into the beam will both save time and improve the figure of merit.

Regarding the latter, the figure of merit for polarized target experiments is proportional to the integrated luminosity times the square of the target polarization. So, for instance, running with an average deuteron polarization of 35% instead of 28% (which is quite realistic given our experience with fully irradiated ND3 material) will yield an improvement of nearly 1.6 in this figure of merit. In combination with a preference for running on ND3 vs. NH3 (see below), we believe we can nearly double the equivalent “figure-of-merit adjusted PAC days" for ND3. This doesn’t yet include improvements in running efficiency and beam current (the latter made possible by recent advances in AI-supported tracking).  
> 
> Also, when you write in the third-to-last sentence of the report
> "... mostly due to (deuterated) ammonia samples ..." do you mean that
> measurements with ND3 were more affected by the pre-irradiation problem
> than those with NH3, or is the problem ND3-NH3 symmetric? Because if it
> is not symmetric wouldn't it make sense to favor ND3 for the remaining data taking?
> (Related to this, I am confused by your Beam Requirements List which looks like you
> are asking for 40 days (960 hours) for each of the 5 targets.)
> 
I apologize that our beam requirements list may have been a bit confusing. You are correct that we will split the 40 days between all different targets, with the largest fraction reserved for ND3 (for the reasons you list), followed by NH3. The remaining targets are auxiliary and will account for less than 15% of the overall beam time.
> 
> Thank you for any comments you can provide.
> 
> Best regards,
> Kresimir