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Please look at this:</div>
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<a href="https://halldweb.jlab.org/DocDB/0066/006668/001/primexd-igal-jaegle-01112024.pdf" id="LPlnk234938">https://halldweb.jlab.org/DocDB/0066/006668/001/primexd-igal-jaegle-01112024.pdf</a></div>
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tks ig.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> gasparan <gasparan@jlab.org><br>
<b>Sent:</b> Friday, November 1, 2024 12:15 PM<br>
<b>To:</b> Igal Jaegle <ijaegle@jlab.org><br>
<b>Cc:</b> primexd@jlab.org <primexd@jlab.org>; Malte Albrecht <malte@jlab.org>; Justin Stevens <jrsteven@jlab.org>; Eugene Chudakov <gen@jlab.org>; Shepherd, Matthew <mashephe@indiana.edu><br>
<b>Subject:</b> Re: [Primexd] Questions on the PrimEx analysis strategy</font>
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Hi Igal,<br>
<br>
I see we have some good agreements on some parts and still have some<br>
different interpretations, especially on the Nuclear Incoherent part.<br>
Let's discuss this part in our upcoming meeting(s).<br>
<br>
Best,<br>
Ashot<br>
<br>
<br>
On 2024-10-31 15:13, Igal Jaegle wrote:<br>
> Thank you, Ashot, for finding the time to give your answers in your<br>
> busy schedule.<br>
> <br>
> Questions #1, I see that we are converging toward the same answer.<br>
> <br>
> Questions #2, my understanding is that Ilya used different elementary<br>
> amplitude scenario/model for the Nuclear Coherent but these changes<br>
> were not applied to the Nuclear Incoherent or what you call<br>
> background. I do not agree with this approach. If the elementary<br>
> amplitude used in the Nuclear Coherent is changed then the exact same<br>
> changed must be applied to the Nuclear Incoherent part. This cannot be<br>
> neglected and looking at the variation of the chi^2 will not capture<br>
> correctly the systematic error linked to the model dependence.<br>
> <br>
> Here by different models, I am also referring to the inclusion yes<br>
> or no of the quasi-free Primakoff/Coulomb and more importantly the<br>
> corresponding interference between the quasi-free Primakoff/Coulomb<br>
> and rho+omega terms.<br>
> <br>
> Questions #3, we do not agree. Any changes to the elementary<br>
> amplitudes contributing to the Nuclear Coherent term must also be<br>
> applied to the Nuclear Incoherent term because any changes to the<br>
> elementary amplitudes will change automatically the shape of the<br>
> Nuclear Incoherent particularly at small angle particularly for the<br>
> eta case.<br>
> <br>
> tks ig.<br>
> <br>
> -------------------------<br>
> <br>
> From: gasparan <gasparan@jlab.org><br>
> Sent: Thursday, October 31, 2024 2:10 PM<br>
> To: Igal Jaegle <ijaegle@jlab.org><br>
> Cc: primexd@jlab.org <primexd@jlab.org>; Malte Albrecht<br>
> <malte@jlab.org>; Justin Stevens <jrsteven@jlab.org>; Eugene Chudakov<br>
> <gen@jlab.org>; Shepherd, Matthew <mashephe@indiana.edu><br>
> Subject: Re: [Primexd] Questions on the PrimEx analysis strategy<br>
> <br>
> Hi Igal,<br>
> <br>
> Here are my initial answers to your three basic questions outlined in<br>
> your recent text. The text is also attached to this email<br>
> and it is not edited for a wider use.<br>
> <br>
> Question #1<br>
> Which process(es) can we measure?<br>
> My answer:<br>
> If one includes the BCAL in coincidence with the eta detected in the<br>
> FCAL then the list of measurable processes is rather large, including<br>
> some elastic and very many inelastic reactions.<br>
> However, we cannot measure the gamma + He4 -> eta + He4 elastic<br>
> process<br>
> at these small angles since recoil He4 (or alpha) can not reach to the<br>
> <br>
> BCAL sensitive area due to its small recoil energy. With that in mind,<br>
> <br>
> all Primakoff type experiments so far are designed to not attempt<br>
> measuring the recoil nuclei since it is not possible at ~~1-degree<br>
> angles. In particular, our current eta-proposal is designed/approved<br>
> without measuring the recoil alpha particles in the elastic reaction.<br>
> Rather we assume that at these angles (0-4 degrees) the events without<br>
> <br>
> the recoil alpha detection can be: (a) Primakoff coherent; (b) nuclear<br>
> <br>
> coherent; (c) interference between them; (d) all kind of incoherent<br>
> and<br>
> inelastic processes having an eta as a one of final states. We call<br>
> the<br>
> (d) as a background in our experiment(s).<br>
> The remaining question is how to identify them and fit out underneath<br>
> of<br>
> the Primakoff part but, this is a separate question.<br>
> <br>
> Question #2<br>
> Can we rely on only one model and/or only one scenario for the<br>
> radiative<br>
> decay width extraction?<br>
> My answer:<br>
> It is always better to have more than one model to use in the<br>
> extraction<br>
> process (since any model is not a fundamental theory, also includes<br>
> some<br>
> limited information only). If we succeed to have at least two models,<br>
> we<br>
> need to use them both. If we do not have the second model, then we<br>
> will<br>
> rely on it and state it in the publication.<br>
> About the “…only one scenario…”. Obviously, it is better to<br>
> have two or<br>
> more ways to extract the decay width. In pi0 PrimEx in Hall B we had<br>
> 3.<br>
> Here we are trying hard to have 2 at least.<br>
> <br>
> Question #3<br>
> Can the built-in model interdependence between the Nuclear<br>
> Incoherent<br>
> term and the Primakoff and Nuclear Coherent terms be neglected?<br>
> My answer:<br>
> This question needs more clear wording to try answering it. However, I<br>
> <br>
> will guess the question and try to answer it. Two processes (mentioned<br>
> <br>
> above) (a) Primakoff (that is electromagnetic coherent exchange<br>
> reaction) and (b) the “Nuclear coherent” (that is the same only<br>
> with a<br>
> hadronic exchange) kinematically (and quantum mechanically) are the<br>
> same<br>
> (if you want, similar) elastic and coherent processes. They can be<br>
> simulated by theory very accurately. Small exception is some constants<br>
> <br>
> and parameters, mostly for the nuclear coherent part. In addition,<br>
> since<br>
> they are quantum mechanically similar, they have an interference term<br>
> as<br>
> a process, this is also a predictable thing with the phase angle.<br>
> The so-called “incoherent part” in reality is all processes other<br>
> than<br>
> first two. We call them as a “background” in the Proposal.<br>
> The short answer: If we have all these 4 processes simulated<br>
> (predicted)<br>
> by model(s) then we should not “… neglect…” or ignore any<br>
> process, we<br>
> simply include them in our extracted cross section for all forward<br>
> angles. This is related to the good case when we are hoping to 1-3%<br>
> extraction. Since (unfortunately) we are not there yet there are<br>
> several<br>
> variations in my previous statement. That is a separate subject, and<br>
> we<br>
> had discussed them in our meeting many-many times.<br>
> <br>
> Best,<br>
> Ashot<br>
> <br>
> On 2024-10-18 12:08, Igal Jaegle via Primexd wrote:<br>
>> Hi, Ashot,<br>
>> <br>
>> I put into a note my questions,<br>
>> <a href="https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668">
https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668</a><br>
>> [1].<br>
>> <br>
>> A dedicated PrimEx discussion at the GlueX Physics Working Group<br>
>> Meeting would be highly beneficial, especially if there are<br>
> differing<br>
>> perspectives on how to address these questions. We would greatly<br>
>> welcome such a discussion.<br>
>> <br>
>> tks ig.<br>
>> <br>
>> Links:<br>
>> ------<br>
>> [1]<br>
> <a href="https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668">https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668</a><br>
> [1]<br>
>> _______________________________________________<br>
>> Primexd mailing list<br>
>> Primexd@jlab.org<br>
>> <a href="https://mailman.jlab.org/mailman/listinfo/primexd">https://mailman.jlab.org/mailman/listinfo/primexd</a><br>
> <br>
> <br>
> Links:<br>
> ------<br>
> [1] <a href="https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668">
https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668</a><br>
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