[d2n-analysis-talk] Neutron extraction for A1

[Diana Parno]

Brad,

This is an excellent point. Wally's previous work should cover g_1 and  
g_2, though we may need some more guidance as to how to perform the  
actual extraction, but d2 is different.

Of course, if our d2 measurement is solely in the DIS region, then we  
probably don't need the full x-dependent treatment. My recollection  
was that the LHRS kinematic settings (which dictate the d2 kinematics)  
were all DIS -- is that correct?

I went back to the d2n 6-GeV proposal to see what the original  
strategy was, but I only see a discussion of corrections to g1 and g2  
to extract g1n and g2n -- I don't see a global strategy for extracting  
the fully realized d2n from d2n(3He). Was this initially in the plan,  
or is this a new hope based on recent interest in this area from Wally  
and others? I can certainly email Wally about the feasibility of doing  
an x-dependent d2n calculation alongside A1n and A2n, but it would be  
helpful for me to know what we already know.

Best,
Diana

On Jun 15, 2011, at 2:16 PM, Brad Sawatzky wrote:

> Just a couple comments on issues to keep in mind.
>
> Note that we'll want to have the information available to correct the
> g_1(x,Q2), g_2(x,Q2) points individually, _and_ to be able to correct
> the d2(Q2) term as a 'unit'.  That is we'll want to be able to apply a
> correction to the already-integrated d2 matrix element, rather than
> correct the individual integrand points prior to integration.
>
> (We'll probably do it both ways, but the latter method should result  
> in
> a smaller systematic uncertainty for the final d2n value.)
>
> -- Brad
>
> On Fri, 10 Jun 2011, Diana Parno wrote:
>
>> Wally Melnitchouk and I met yesterday afternoon and had a very
>> productive discussion about going from 3He to the neutron. Here's the
>> executive summary:
>>
>> - The Bissey et al method (which I presented in last week's analysis
>> meeting) assumes no x-dependence (so, it's not quite as "complete" as
>> the title describes!). This is probably safe for our DIS points but
>> definitely not for our resonance points.
>>
>> - Wally recommends the more general, x-dependent method in Kulagin  
>> and
>> Melnitchouk, PRC78 065203 (2008). Unfortunately, they've only worked
>> out this method for g_1 and g_2 on the neutron, not on the
>> asymmetries. He thinks that the extension to A_1 and A_2 would be
>> relatively straightforward and a useful problem, and predicts that he
>> should have something for us on the general time scale of three  
>> months
>> (see email). He's excited at the prospect of experimental interest in
>> the method described in the 2008 paper. From our end, I think a few
>> months is quite reasonable and will give us time to pursue the 5.9- 
>> GeV
>> dataset, pair-production corrections, radiative corrections, etc.
>>
>> - He agrees with my worry about Bissey et al's assumption that A2 is
>> close to zero, but we think that (for a first look at the DIS data
>> points), their equation should be very easily extensible to g1/F1
>> without having to make that assumption. I think the math on that is
>> relatively simple and I'll work on it next week.
>>
>> - He doesn't think that anti-shadowing is a big deal for our low-x
>> point -- probably a few percent. On the other hand, we're worrying
>> about a few-percent EMC effect, so perhaps it's worth some study. His
>> own work includes the delta isobar but not shadowing/anti-shadowing.
>>
>> Brad, Matt, and Dave: I enjoyed seeing you at the Hall A meeting!  
>> Hope
>> we'll cross paths in person some time again soon. It was a very
>> productive and interesting couple of days.
>>
>> Enjoy your weekends,
>> Diana
> -- 
> Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C /  
> C111
> Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
> The most exciting phrase to hear in science, the one that heralds new
>  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov
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