[G8b_run] FROST meeting

Thu Jun 30 08:59:16 EDT 2011

Ken,

I look forward to seeing the results of this technique. When do you think 
that you can use this new method to get the ratio of polarizations? I 
would very much like to get that information. I have had a hard time using 
FROST pi0 data to obtain the ratio of polarizations.

Thanks for your time.

Sincerely,
Michael

On Thu, 30 Jun 2011, Ken Livingston wrote:

> 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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>>>>     2. Enter 7-digit access code, *7440953* followed by *#*
>>>> 
>>> 
>