[Gpdtc] Wednesday....

[David Richards]

Dear Wally,

Thank you.

On Jan 10, 2022, at 11:02 PM, Wally Melnitchouk <wmelnitc at jlab.org<mailto:wmelnitc at jlab.org>> wrote:

Thanks, David, for putting this together.

On slide 4, 3rd bullet: a suggestion for alternative wording for the is "Development of global QCD analysis methods with uncertainty quantification for PDFs and TMDs, and their extension to (3D) GPDs."

Done...

Slide 5, point #1: there might be potential uncertainty about what exactly "QCD-inspired descriptions of GPDs and CFFs" refers to. If it is some other than model calculations of GPDs and CFFs, perhaps this should be specified a bit more explicitly?

Peter had a somewhat similar comment (and to also to your point ^^^ below).  What I’ve done is to move any talk about QCD models to bullet 4 as "confronting QCD-inspired descriptions of hadrons to identify the key DOF”.   So the extraction of GPDs is model independent (to the extent possible), but models are valuable in learning how QCD works, cf spectroscopy and the quark model, etc.

Slide 5, point #2: is it just the x dependence of GPDs that is of interest, or also the ξ (skewedness) dependence, along with the t dependence?

I’ve modified this - point being that they are 3D distributions, as opposed to the 2D GFF computed previously on the lattice, and indeed that are most closely related to experimental observables.

Slide 5, point #3: "Global QCD analysis with uncertainty quantification to extract..." Again, I would like to be careful about how "QCD-inspired descriptions" would be used to extract GFFs and GPDs, as we don't want to imply that models will be used to help determine these from data (since we may want to "test" models rather than assume them).



^^^
Slide 5, point #5: what is the significance of this point being in parentheses?

Simply it may or may not be a task - also in our GPD meeting at JLab several years back, one topic was where the boundary lay between “experiment” and “theoretical analysis”, and the consensus seemed to be that radiative corrections lay in the former.

Slide 6: maybe put dots after a bullet below "William and Mary" to suggest other institutions may be involved too?

Done…

Regards,
David

Wally


________________________________
From: Gpdtc <gpdtc-bounces at jlab.org<mailto:gpdtc-bounces at jlab.org>> on behalf of David Richards <dgr at jlab.org<mailto:dgr at jlab.org>>
Sent: Monday, January 10, 2022 5:06 PM
To: gpdtc at jlab.org<mailto:gpdtc at jlab.org> <gpdtc at jlab.org<mailto:gpdtc at jlab.org>>
Subject: [Gpdtc] Wednesday....

Hi All,

Before I go too far down writing something for Wednesday, please find attached some first thoughts - without figures.


The first couple of slides are basically some observations about the call, and what are likely to be the criteria (NB I could have also included diversity in all its interpretations…).
The real issue is how much should we discuss about our discussions and aims in the context of this meeting (transparency 5), and should I say (verbally or on paper) who is currently in our discussions (page 6) - I’ve listed institutions + (incomplete) names.  I make the point on page 3 that the creation of long-term positions is an important task, but I’m not sure I would want to say in writing where those positions might be.

I’ve taken the Executive Summary document, and page 5 is basically the extraction of that.  But we had some discussion before the break as to what the focus should be - for example, purely to extract GPDs, or aim to learn something more about the internal dynamics of hadrons (ie as Christian was discussing).  Similarly, Global Fitting or are there some better words we can use?


Regards,
David

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