[Primex] eta proposal for PAC35

Tue Nov 3 11:35:48 EST 2009

Dear Tulio,

Thanks very much for your comments. Here are answers:

(1) Of course we should have NI term in Fig. 5. The current one in the draft is 10 year old. The NI term is missing for some reasons. We will update it in next couple weeks.     

(2) Fig. 30 is from last year for 45 days. We are working on the update. On the other hand, I don't think there are any existing eta Primakoff data on proton target (at least published data). For proton, fortunately, there is no "nuclear incoherent" contribution at all in that region. In addition, Laget's calculation demonstrates that he can fix the relative sign of phase angle.  Experimentally, we can measure the nuclear coherent production very precisely outside of Primakoff peak since the it drops slowly at larger angles. Therefore, we can determine the phase angle from the experiment data.   

(3) I agree with you that 12C is an very interest target. However, adding it into the proposal will make our total beam time over 100 days. We are afraid that PAC might not like it if we ask too many days at the beginning.

Liping

-----Original Message-----
From: tulio at if.usp.br [mailto:tulio at if.usp.br] 
Sent: Tuesday, November 03, 2009 9:34 AM
To: Gan, Liping
Cc: primex at jlab.org
Subject: Re: [Primex] eta proposal for PAC35

Dear Liping,

I have few questions related with the ETA proposal.

(1) You present in Fig.5 a prediction for coherent photoproduction of eta mesons
from 4He, since the NI term is not added and the 4He is presumably in the G.S.
However, you show in Fig. 19 that the energy resolution of the FCAL has a sigma
of the order of 270 MeV.  So, my question is how you can be sure that additional
channels, including isobar excitation, do not contribute to the extracted
angular distributions? For the case of PrimEx a much better energy resolution
was achieved and we had to account for the NI part anyway. In case you are
considering the NI part for 4He, then we could verify qualitatively that it
would be very difficult to disentangle unambiguously the NC and NI parts of the
cross section (Fig. 5). The NC peak is very small and has a long tail to larger
angles. Maybe it would be interesting to perform measurements in light nuclei
as well. The NC peak goes with ~ A^2.

(2) You present in Fig. 30 a simulation based on Laget's calculation for the
angular distribution of eta mesons (dN/dtheta) from a 45 days run. First, I
think it would be interesting to show the predictions of Laget calculation on
top of some experimental data. These data at forward angles are not very
precise and I am sure that the PrimEx group will improve very significantly
this scenario, but it would be interesting to show that Laget's calculation
"fits" the old dataset. The second comment is that the Primakoff peak (0.1 -0.2
deg.) is accompanied by a very large overlap with the INT and NC contributions.
We faced similar problems with pi0 photoproduction, where the Primakoff peak
angle is approximately 16 times lower than for the eta. So, my question is how
the proton data can be effectively used to extract the decay width? In am
convinced that additional and high precision proton measurements are essential
to constraint the amplitudes of the Regge model, but the result of the
extracted decay width using only the proton and 4He targets will be strongly
correlated with the phase-shift.

(3) Just few comments about the choice of targets: You mention on p. 13 that
light nuclei, such as 12C, are "another improvement" using the 12 GeV upgrade.
However, the 12C target is not included in the proposal. You also mention that
the proton and 4He would allow checking the Z dependence of the Primakoff peak.
If that is the case, then what would be sufficiently good to discard 12C from
the analysis? The number of Primakoff events from eta photoproduction from 12C
is one order of magnitude higher than 4He and almost 40 times higher than the
proton. Following your beam time request, 40 days on proton would represent 1
to 2 days in Carbon. Another important aspect to mention is that the neutron
cross section was never measured and maybe you could consider using also the
deuteron target, although this would probably need a much higher beam time
request.
With my best regards,
-Tulio.

> Rory,
>
> This is the same physics proposal as we submitted to PAC34 last year. The
> only difference is that we suggest to use standard GlueX calorimeter FCAL
> instead of PrimEx HYCAL in this new proposal. On the other hand, this is a
> draft proposal only. We must submit it to Eugene this week in order to start
> the process to be reviewed and discussed by hall D staffs and GlueX
> collaboration. If someone need more time to study the proposal, it is
> perfectly all right. We can always add people later on once they decide to
> join us before the final proposal.
>
> Other collaborations at Jefferson lab have such kind of calls regularly. We
> are not the only one.
>
> Therefore, whoever responding our call by 6:00pm on Nov 3 (tomorrow), his/her
> name will be on this eta draft to be submitted to Eugene. However, we still
> welcome anyone to join us after.
>
>
> Liping
>
>
>
>
> -----Original Message-----
> From: Rory Miskimen [mailto:miskimen at physics.umass.edu]
> Sent: Monday, November 02, 2009 12:30 PM
> To: Gan, Liping
> Cc: primex at jlab.org
> Subject: Re: [Primex] eta proposal for PAC35
>
> Liping,
>
> It's a reasonable courtesy to give people a week or two to read and
> study a proposal, to see
> if they want to join.  Tomorrow by 6 PM is too soon.
>
> Rory
>
>
>
> Gan, Liping wrote:
> >
> >
> >
> >
> >
> > Dear PrimEx friends,
> >
> >
> >
> > Since two years ago,  we have been developing the eta Primakoff
> > experiment in Hall D. In the past month, we are actively discussing
> > different aspects of the new proposal and new simulation results in
> > the regular PrimEx weekly meetings. We plan to submit this proposal to
> > coming PAC35 with the standard GlueX setup. In order to be reviewed by
> > the Hall D staffs and GlueX collaboration we must submit a draft to
> > Eugene by this Wednesday (Nov 4).
> >
> >
> >
> > Attached file at http://people.uncw.edu/ganl/primex/index.htm is our
> > current draft. We will continue working on it up to Dec 14, the
> > deadline for the PAC.  We would like to invite you to join this
> > exciting project with your contributions to the proposal and the
> > experiment. If you would like to have your name on the proposal,
> > please send me an e-mail with participant names from your institute by
> > Tuesday (Nov 3) at 6:00pm.
> >
> >
> >
> >  Best regards,
> >
> >
> >
> >  Liping
> >
> >
> >
> >
> >
> >
> >
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