[Primexd] Questions on the PrimEx analysis strategy

Igal Jaegle ijaegle at jlab.org
Fri Nov 1 13:22:40 EDT 2024 

Please look at this:

https://halldweb.jlab.org/DocDB/0066/006668/001/primexd-igal-jaegle-01112024.pdf

tks ig.
________________________________
From: gasparan <gasparan at jlab.org>
Sent: Friday, November 1, 2024 12:15 PM
To: Igal Jaegle <ijaegle at jlab.org>
Cc: primexd at jlab.org <primexd at jlab.org>; Malte Albrecht <malte at jlab.org>; Justin Stevens <jrsteven at jlab.org>; Eugene Chudakov <gen at jlab.org>; Shepherd, Matthew <mashephe at indiana.edu>
Subject: Re: [Primexd] Questions on the PrimEx analysis strategy


  Hi Igal,

  I see we have some good agreements on some parts and still have some
  different interpretations, especially on the Nuclear Incoherent part.
  Let's discuss this part in our upcoming meeting(s).

  Best,
  Ashot


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