[Primexd] Questions on the PrimEx analysis strategy

Fri Nov 1 14:49:18 EDT 2024

   Hi Igal,

  I went through the pointed text. Our old question is: what is the 
Nuclear Incoherent
  amplitude (or the process). We first need to define it clearly then to 
see its
  properties.
  Ashot

On 2024-11-01 13:22, Igal Jaegle wrote:
> 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]
>>> [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
>>> Primexd at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/primexd
>> 
>> 
>> Links:
>> ------
>> [1]
> https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668
> [1]
> 
> 
> Links:
> ------
> [1] https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=6668