[Halld-physics] draft text of the eta-Primakoff proposal update

[Curtis A. Meyer]

Hi Ashot -

    I went through your draft this morning. Overall, it looks to be in 
very good shape, and
you certainly benefit from have done the proposal only a year ago. I did 
have a few comments
on things and hope that the following feedback is useful.

  *) In section 1 where you give the Pseudoscalar mixing angle with a 
very precise value. I am
not sure that it is possible to measure this so accurately. There are 
too many experimental
biases and assumptions that go into the wide range of measurements.  For 
example, the 2010
PDG lists the mixing angle as -18+-2  from eta-prime -> two gamma vs 
eta-> two gamma,
but it is -24 from eta-> 2gamma vs pi0-> 2gamma. Klempt and Zaitsev 
(Phys. Rep. 454, p.1  2007)
give a combined number of -13.2 +- 1.2  when looking at radiative decays 
to eta and eta-prime
and on page 18 of there report, Figure 3 shows a nice contour plot of 
this. The bottom line
is that It is hard to believe that one can measure this to better than 
1-2 degrees as the wide
range of definitions will mess distort your result. While an improved 
gamma-gamma width
will no doubt impact this mixing angle, I do not believe that it will 
improve the accuracy to
the level that you quote.

*) I liked the discussion on the new theoretical work. That is important 
to see.

*) At the end of section 1 where you talk about the comp-cal. Do you 
have GEANT simulations
for the performance of this down stream of the FCAL? It would certainly 
be very nice to be able
to use it there, but I am concerned about all the the scattering from 
the walls of the hole in the
FCAL. You probably need to expand this a bit to show your detailed MC 
results. Particularly
because this is used to measure the Compton events accurately and is 
crucial to your argument
for separate beam time.

*) You discuss the coplanarity condition as an important cut for pulling 
out Comptons from the
data stream, and show how the magnetic field destroys this. That is nice 
to see. My question is
about the impact of the material in GlueX on this angle? Unfortunately. 
there is material in
the FDCs along the beam line that also might impact this. Do you have an 
estimate for this
effect?

*) While the 11 days that you were able to shave off the beam-time 
request are good, you may
want to caveat that those shared days need to occur close to the start 
of your running. If we
hit a year where only PrimEx runs, then those days would need to be part 
of your requested beam
time. It is probably worth pointing this out in your explanations.

   Cheers -- Curtis

On 11/29/10 5:53 AM, Ashot Gasparian wrote:
>
>   Dear Hall D Collaborators,
>
>  We are required to submit a short update for the eta-Primakoff
>  proposal to this upcoming PAC37 for the beam time assignment and
>  scientific rating.
>  The proposal was approved a year ago by PAC35.
>
>  The first draft of the suggested update is in the attachment of
>  this email. The submission deadline is on this Wednesday, so you
>  will have a few days to send your critical suggestions and questions
>  to us to make this document better for the submission.
>
>  Thank you for your participation and valuable support,
>  Ashot, Liping
>
>
>
> .............................................................
> Ashot Gasparian                    Phone:(336)285-2112 (NC A&T)
> Professor of Physics
> Physics Department                       (757)-269-7914 JLab
> NC A&T State University              Fax:(757)-269-6273 JLab
> Greensboro, NC 27411               email: gasparan at jlab.org
> .............................................................
>
>
> _______________________________________________
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-- 
Prof. Curtis A. Meyer		Department of Physics
Phone:	(412) 268-2745		Carnegie Mellon University
Fax:	(412) 681-0648		Pittsburgh PA 15213-3890
cmeyer at ernest.phys.cmu.edu	http://www.curtismeyer.com/


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