[b1_ana] b1 phone meeting April 29 (note time)

[Dustin Keller]

yes I think for the most part he was not saying we should look at
b1 from the difference instead of Azz, he was just pointing out
that it too can be extracted from the same exact data without
using F1.  Azz of course will give smaller errors.  Outside of
that he was just concerned with how f should be in the Azz equation
which we figured out.  Even though the errors are much larger in
some cases its really good that we have multiple route to our
observables.

dustin

On Wed, 1 May 2013, Patricia SOLVIGNON wrote:

> Hi Oscar.
>
> I think we are still running in the same problem as at the last time we propose the sigma_para - sigma_perp method. It is the difference of two huge numbers to extract a very small number. The method of using two cups work well for getting g1 and control its systematics because the unpolarized cross section never comes into play. Just looking at equation (2) of your note tells me that we are back to the same issue as the last proposal. From the statistics point-of-view, it is true that the unpolarized cross section using the method you propose will cancel but it will stay in the systematics.
> I convince myself a while ago that there is no other way to get b1 than by the asymmetry method because it is the only way to truly cancel the unpolarized cross section contribution in the statistics and in the systematics as well. Of course the asymmetry method suffers from the statistics but that can be overcome with beam time request and/or going to large acceptance spectrometer. If I remember well, Dustin came up with the same conclusion.
>
> Bests,
> Patricia
>
> -- 
> Patricia SOLVIGNON
> Staff Scientist
> Jefferson Lab
>
> Current address :
> Jefferson Lab
> Suite 6, MS. 12H4                               Room C121 (Cebaf Center)
> 12000 Jefferson Avenue                      Office:   (757)-269-6933
> Newport News, VA 23606
>
> On Apr 30, 2013, at 5:59 PM, O. A. Rondon <or at virginia.edu> wrote:
>
>> Hi Dustin,
>>
>> Dustin Keller wrote:
>>> You can only benefit from the systematic reduction if you us Azz as
>>> discussed yesterday.  But at this point I am not partial.
>>>
>>> dustin
>>>
>>
>> In the experiment, we only have counts. What we need to show to the PAC
>> is how we go from the counts Npol and Nu, to Azz or b1. A measured
>> quantity needs to be on one side and physics on the other. Lets say we
>> start with your ratio Npol/Nu - 1 = Pzz*Azz, which only requires Pzz >0.
>>
>> We need to prove that the lhs reproduces the rhs. We have, in general,
>> N = Q*e*A*l*sigma. But since N are counts from everything in the target,
>> it is not a simple matter of canceling quantities that stay the same
>> when the polarization changes:
>>
>> Npol = Qpol*epol*Apol*lpol*sigma_pol
>>     = Qpol*epol*Apol*lpol*[(sigma_N+3*sigma_Dpol)*pf + sigma_He*(1-pf)]
>>
>> Nu   = Qu*eu*Au*lu*[(sigma_N+3*sigma_D)*pf + sigma_He*(1-pf)]
>>
>> sigma_N and sigma_He are the same, always unpol. And
>> sigma_Dpol = sigma_D(1+Pzz*Azz).
>>
>> Then, since Apol = Au = A, and lpol = lu = l,
>>
>> Npol/Nu =
>> (Qpol/Qu)*(epol/eu)*[(sigma_N+3sigma_D(1+ Azz*Pzz))*pf+..)]/[(sigma_N+..
>>
>> where I just put ..., because I don't see how it can be simplified to
>> just leave Azz*Pzz + 1, to equal the rhs.
>>
>> On the other hand, if instead of taking the ratio Npol/Nu first, we take
>> the difference first, it's indeed possible to isolate the required
>> Pzz*b1 on on side, like I do in my draft, eq. (19) or (20). And in
>> fact, we don't even need to bother with Azz, because we get b1 without
>> having to multiply Azz by F1, introducing one more systematic error.
>>
>> So, in summary, once one substitutes all the ingredients for your sigmas
>> we get, or ought to get, eq.(19) or (20) back.
>>
>> In both of those equations, the systematics for Pzz, A, and l(pf) are
>> normalization factors, just like we want them to be, for control of
>> systematics, but the charge and the detector efficiency are not common
>> factors, they depend on the period when the data are taken, either pol.
>> or unpol.
>>
>> My point is that for the proposal, we must spell this all out, to give
>> explicit sources of errors, and to calculate times or statistical errors
>> correctly. For example, the statistical error must be sqrt(Npol + N_U) ~
>> sqrt(2N), because it is just the error of a difference, etc.
>>
>> We need to have a consensus on how the method is going to be described
>> in the proposal, which needs to be done in the most precise way to avoid
>> any confusion due to ambiguities.
>>
>> Cheers,
>>
>> Oscar
>>
>>
>>> On Tue, 30 Apr 2013, O. A. Rondon wrote:
>>>
>>>> Hi,
>>>>
>>>> Since I couldn't stay until the end of the meeting, and I don't think
>>>> there will be minutes of it, I would like to share some ideas for the
>>>> proposal draft.
>>>>
>>>> Basically, what we need is an equation with the measured quantity on one
>>>> side and b1 or Azz on the other. Based on what I think the consensus
>>>> was, to measure polarized minus unpolarized counts on a single cup with
>>>> the target field aligned along the beam, I've updated the draft of my
>>>> method, see subsection 0.2, which discusses this. Eq. (19) or eq. (20)
>>>> meet the conditions stated above. This is the approach I would subscribe
>>>> to, unless there is another version that is shown to also represent the
>>>> procedure, which should be circulated as soon as possible. The draft
>>>> is here
>>>> http://twist.phys.virginia.edu/~or/b1/b1_method-v2.pdf
>>>>
>>>> Cheers,
>>>>
>>>> Oscar
>>>>
>>>> _______________________________________________
>>>> b1_ana mailing list
>>>> b1_ana at jlab.org
>>>> https://mailman.jlab.org/mailman/listinfo/b1_ana
>>>>
>>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> b1_ana mailing list
>> b1_ana at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/b1_ana
>
>