[Tpe] new Gep paper

[Guy Ron]

Larry is correct.
One additional possible problem with the internal target measurement is 
a possible uncertainty in the polarization
direction. Note however, that there is also some discrepancy (which is 
being looked at) with the GEp-I results, which did use a recoil 
polarization measurement.
Our upcoming experiment, scheduled to start Nov 2011 will extend the 
range of the previous measurement to lower Q^2 using a solid polarized 
target (the UVa target). Hopefully this will help resolve any discrepancy.
As Larry mentioned, we are very confident about our current result since 
Xiaohui Zhan, who performed the analysis, was very meticulous in testing 
for any possible systematic effects in the measurement.

Guy

On 2/4/11 9:23 AM, Larry Weinstein wrote:
> I spoke to Guy Ron this morning about that.  He is not sure what the
> difference is between the JLab measurements and the Bates BLAST
> measurement, but he is pretty confident of the JLab measurement.  There
> are a few sources of uncertainty in those kinds of measurements.  The
> JLab measurement is a polarization transfer measurement, measuring the
> polarization of the outgoing proton [p(pol e, e' pol p)].  The Bates
> measurement is an internal polarized gas-jet target measuring [pol p(pol
> e, e' p)].
>
> It is tough to know your target polarization precisely.
>
> Guy can comment more if he wants.
>
> Will Brooks wrote:
>> Well, it's very good news for us if it turns out to be true, since we
>> can clearly span their Q2 range and far beyond. The new measurement
>> seems to be systematically different from previous analyses, beyond the
>> uncertainties.
>>
>> http://arxiv.org/abs/1102.0318
>>
>>
>> On 2/3/11 6:51 PM, Larry Weinstein wrote:
>>
>>> Dear TPE Folks,
>>>
>>> There is a new paper from Hall A on the low Q2 Gep/Gmp ratio:
>>> arxiv 1102.0318
>>> Zhan et al
>>>
>>>
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