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

Tue Nov 30 17:31:55 EST 2010

Thanks Liping -

    I agree that within a particular model, you can measure the mixing 
angle as
accurately as you want. Unfortunately, I am not convinced that one 
particular
model is so much better than all the rest.  Thus the uncertainty based 
on the different
models must be many degrees.  Even the simple assumption that there is a 
glueball
component in the eta/eta-prime system throws a non-negligible error into 
this.

    Curtis


   my point is not so much that in a given model, you can m
On 11/30/10 5:02 PM, Gan, Liping wrote:
> 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/
>
>
>
>


-- 
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/