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Hi Karl,<br>
<br>
I agree that this is what we concluded with at the end of the
meeting yesterday. <br>
<br>
1 thing that I just wanted to mention; <br>
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.
<br>
<br>
Also, Steve Wood has offered to take an early look at our numbers
before we submit. This might be a good idea.<br>
<br>
Narbe<br>
<br>
<br>
On 04/26/2013 12:22 PM, Karl Slifer wrote:<br>
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cite="mid:CAKYfHovAq-xqnQmjV3-_pYoSCBcWeNZ8E2+vFg2qQNo7Kw1m1g@mail.gmail.com"
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Hi,
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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. </div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.<br>
</div>
<div><br>
</div>
<div>my few further cents,</div>
<div><br>
</div>
<div> Karl</div>
<div><br>
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<div><br>
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<div class="gmail_extra"><br clear="all">
<div>
<div>
<div>
<div>---<br>
<div>Karl J. Slifer
<div>Assistant Professor</div>
<div>University of New Hampshire<br>
<div>Telephone : <a moz-do-not-send="true">603-722-0695</a></div>
</div>
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<br>
<br>
<div class="gmail_quote">On Fri, Apr 26, 2013 at 11:04 AM,
Dustin Keller <<a moz-do-not-send="true"
href="mailto:dustin@jlab.org">dustin@jlab.org</a>> wrote:<br>
<blockquote class="gmail_quote">
As I mentioned in the meeting using the notation Axx can be<br>
mis-leading especially in the case of DIS where azimuthal<br>
control is not obvious. However the relationship for<br>
sigma^{+/-} for m=+1,-1 is
sigma^{+/-}=sigma^u(1+(1/2)AzzPzz).<br>
If you believe that then Axx=Azz, and the conclusion is the
same.<br>
If you call it Axx or Azz in either case you just measure
the<br>
ratio of polarized and unpolarized cross sections. This
will lead<br>
to a target tensor polarization of about 10%. There are
certainly<br>
other systematic concerns but this is the best we can do
target wise.<br>
<font color="#888888"><br>
dustin<br>
</font>
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