[G8b_run] FROST meeting

[Ken Livingston]

Hi Micheal,
Thank a lot for having a look at that.
I've fixed the missing  parenthesis  and wrong subscripts, and the eqn 
for unpolarized target asymmetry, which was screwed up - none of which 
affect the basic argument. ( I even removed some of the more flippant 
remarks).

The point of this was to look at the best way of using all the 
information, in general, but particularly to get G, since Stuart is 
doing this right now. The possibility of measuring G without knowing the 
photon polarization just drops out.

The aim is to extract as much useful information as possible from the 
data on the carbon and CH2, where any old asymmetry will be good enough 
to give the ratios N_21 and P_21, and the phi_0 offset. The channel 
doesn't matter, we just need as big a signal as possible.  The data only 
has to be binned in E_gamma, but can be integrated over all thetas where 
the asym has the same sign. The values of N_21 and P_21 and phi_0 are 
then applicable to the butanol data for the same E_gamma bins, but any 
theta binning we like. (Actually, as you know we can take phi_0 from one 
enormous asymmetry on C or CH2 covering all E_gamma and theta bins where 
asym is +ve). Ideally this would be done for the channel with the 
highest stats - single pion.

I hope Stuart will test this on his K Lambda data, since he's in the 
process of extracting Sigma and G at the moment.
Maybe, as you say, we won't do any better this way than with the 
polarization from coherent brem calculations. But it's worth investigating.

I believe it was always the intention in these double polarization expts 
to use values of single observables already measured elsewhere in 
dedicated experiments. So we have always assumed that the g8 values for 
Sigma would be used to extract G. Stuart is just comparing his extracted 
sigma with those from G8 at the moment to confirm that they agree, but 
then we expect to use the g8 values in the final extraction of G.

Cheers,
Ken


On 06/29/2011 09:43 PM, Michael Dugger wrote:
> 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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>>>            * UK Toll-Free Number: *08004960576*
>>>            * Other International Toll-Free Numbers:
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>>>     2. Enter 7-digit access code, *7440953* followed by *#*
>>>
>>