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

[Gan, Liping]

Dear Curtis,

I would like to response your first  comment on the mixing angle.  Currently there are different existing schemes  to define the pseudoscalar  mixing angles. The one we described in the proposal (page 6 and 7) is assuming simple mixture of SU(3) octet and singlet states, where the eta and eta-prime decay widths are the inputs to determine the mixing  angle. A recent lattice QCD calculation ( by N.H. Christ et al., arXiv:1002.2999 [hep-lat] Feb 2010)  has confirmed this picture. The error analysis is done by Jose is based on next-to-leading order chiral and 1/N_c expansions. It gives us an estimation how much the mixing angle can be improved by improving the eta decay width under this theoretical frame. 


Liping
________________________________________
From: halld-physics-bounces at jlab.org [halld-physics-bounces at jlab.org] On Behalf Of Curtis A. Meyer [cmeyer at ernest.phys.cmu.edu]
Sent: Monday, November 29, 2010 11:12 AM
To: Ashot Gasparian
Cc: GlueX Physics
Subject: Re: [Halld-physics] draft text of the eta-Primakoff proposal update

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<mailto: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<mailto:cmeyer at ernest.phys.cmu.edu>   http://www.curtismeyer.com/