[G8b_run] FROST meeting

[Michael Dugger]

Ken,

I looked over your method and have a few comments:


* It looks like you are missing closing parenthesis in the equations just 
before Eqn. 4

* You might want to check that all of the subscripts are correct. In Eqn. 
4 you have R_n21*R_n21 and this should be R_n21*R_p21.

* I can't get the same expression as you do for the "Eqn. 4 for 
unpolarized target reduces to..."
Perhaps I am missing something here. I just set Y_1 = 0 and get a 
different expression than what you show.

* It seems to me that the big problem is going to be measuring R_p21. 
R_p21 is the ratio of beam polarization 2 to beam polarization 1, and from 
what I have seen so far (looking at pi0 using the 1.3 GeV coherent edge 
FROST data), the amount of bound nucleon background makes finding this 
ratio very difficult. For g8b, finding the ratio of beam polarizations is 
fairly easy using the forward going pi0 because the forward going pi0 has 
a very large beam asymmetry. For FROST, the dilution is killing us.

* You have the equations:
A = P1*Sigma
B = P1*Y1*G
and use the ratio to get
B/A = Y1*G/Sigma
This is a good idea, and one we should explore. However, if we use a 
previous measurement of Sigma, this is just a fancy way of measuring P1 
using previous measurements of Sigma, and FROST measurements of 
A=P1*Sigma. The question then becomes: What values of Sigma do we use? Do 
we use previous measurements or a parametrization like SAID?

In either case, we have to have a very good measurement of A=P1*Sigma. 
Measuring P1*Sigma will be difficult due to the fact that a raw Sigma 
measurement will have a complicated dependence on the bound nucleon 
contribution that can not be neglected, especially since we would be 
comparing the A=P1*Sigma measurement to previous measurements of Sigma, to 
obtain P1.

I think that this is something worth looking at, but I would not be 
surprised if it turns out that the errors we get for P1 and R_p21 using 
the suggested method ends up being much larger than the systematic errors 
we get using polarizations determined by your coherent bremsstrahlung 
calculations.

Take care,
Michael


On Wed, 29 Jun 2011, Ken Livingston wrote:

> Hi All,
> I've added this link http://nuclear.gla.ac.uk/~kl/g9/G.html to those other in 
> the meeting page. It's an outline of a method for measuring G - making best 
> use of all available information. I also believe this method avoids the need 
> to know the photon beam polarization.
> If anyone has time to have a look before the meeting that would be useful. I 
> could give a summary if required.
>
> Regards,
> Ken
>
> On 06/29/2011 08:19 PM, Eugene Pasyuk wrote:
>> Hi all,
>> 
>> We will have our weekly meeting tomorrow Thursday Jun 30 at 11:30 JLab time 
>> in B101.
>> http://clasweb.jlab.org/rungroups/g9/wiki/index.php/June_30%2C_2011
>> 
>> The g9 meeting will possibly be followed by g8b beam polarization 
>> discussion.
>> 
>> -Eugene
>> 
>> 
>> 
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