[b1_ana] Axx

[Dustin Keller]

Hi,
Getting 20% uncertainty using hole burning for negative tensor 
polarization down to 5% seems a bit of a stretch to me especially given 
the small single people are interested in for b1.  But I'm glad to help in 
anyway I can to try to get it through.

We really should consider the form of
Azz=(2/Pzz)(N^p-N^u)/N^u
it get the uncertainty from 20% to 10%, a much better starting point.

dustin

On Fri, 26 Apr 2013, Karl Slifer wrote:

> Hi,
>
> While it would be easier to run with only positive Pzz, there is no
> technical or theoretical reason that I know of that prevents us from using
> negative pol.  This will require target development to achieve large
> negative as well as positive tensor polarizations, along with careful study
> of the systematics in extracting these values.  I thought we all agreed on
> this yesterday....And I also see no technical or theoretical reason (other
> than it is difficult and will require R&D) which limits the enhanced tensor
> polarization to 10%.  I believe Don, Chris, Josh would all agree with this,
> atleast they all did when I talked to them within the last 6 months.
>
> So to be clear, I believe we can propose an experiment where we enhance the
> m=0 population (via rf saturation or by using two independent microwave
> sources) and measure N_0 unpolarized electrons inclusively scattered while
> in this state, and then we deplete the m=0 state to obtain a positive
> polarization and measure N_1 unpolarized electrons scattered while in this
> state.  Then we form the asymmetry (with appropriate numerical factors).
> The Pzz will not be the maximal positive or negative value in either state,
> but we can correct for this by the relative Pzz in each state.    One
> significant concern is that this introduces time dependent systematics
> since it will likely require some time to switch between the two states.
> This has to be studied, but I do not see it as a fundamental limitation.
>
> After careful study of the systematics, its possible that the cross section
> difference method may well turn out to be the best way to do the
> experiment, but I suspect we will struggle mightily to convince a very
> skeptical PAC in 30 mins that we really can control all the systematic
> effects to the level needed for a cross section measurement.
>
> With this in mind, I think it is reasonable to aim for conditional approval
> based on demonstration of the target performance to the level needed (+-20%
> tensor pol with about 5% relative uncertainty).  I believe we can defend
> these as reasonable goals, although we should get something in the way of a
> support statement from Don or Chris.  And I believe conditional approval is
> a highly desirable state, since the target groups will not be able to
> commit serious R&D to this without an approved experiment for motivation.
> In addition, it opens the door to attract more theory support and start
> consideration of several other possible experiments.
>
> my few further cents,
>
> Karl
>
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> ---
> Karl J. Slifer
> Assistant Professor
> University of New Hampshire
> Telephone : 603-722-0695
>
>
> On Fri, Apr 26, 2013 at 11:04 AM, Dustin Keller <dustin at jlab.org> wrote:
>
>> As I mentioned in the meeting using the notation Axx can be
>> mis-leading especially in the case of DIS where azimuthal
>> control is not obvious.  However the relationship for
>> sigma^{+/-} for m=+1,-1 is sigma^{+/-}=sigma^u(1+(1/2)AzzPzz).
>> If you believe that then Axx=Azz, and the conclusion is the same.
>> If you call it Axx or Azz in either case you just measure the
>> ratio of polarized and unpolarized cross sections.  This will lead
>> to a target tensor polarization of about 10%.  There are certainly
>> other systematic concerns but this is the best we can do target wise.
>>
>> dustin
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>