[b1_ana] Axx

[Narbe Kalantarians]

Hi Karl,

I agree that this is what we concluded with at the end of the meeting 
yesterday.

1 thing that I just wanted to mention;
The time dependence between +/- P_zz could be handled, possibly in the 
sense of systematics, provided that they're both in the same orientation 
(i.e. either para. or perp.) If it were to be a difference of para. and 
perp., then it becomes a major challenge.

Also, Steve Wood has offered to take an early look at our numbers before 
we submit. This might be a good idea.

Narbe


On 04/26/2013 12:22 PM, 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
>
>
>
>
>
>
>
>
>
>
> ---
> 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 
> <mailto: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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