[Frost] Neutron Measurements with FROST

[Igor Strakovsky]

Hi Volker and Frosters,

When I spoke to Eugene privately before meeting then my request was the
same - to study W = 1600 - 1750 MeV range first of all.  The reason was
exactly the same because GRAAL, CB-ELSA, and LNS observations agreed
with our predictions for the N(1680) which we found using modified piN
PWA [PRC69, 035208(2004)].  ChSA helped with some estimations for its
decay modes.  Let me say that prlm GRAAL data shown a good structure in
the K-Lambda final state as well. I do not know what MAMI (B or C) data
are you talking about but I will report CB at MAMI data for gp-->etaP in
two weeks on MENU10.  There is interesting behavior in the differential
cross section around W = 1670 MeV

I do not think that idea that D15(1675) is responsible for this effect
makes any sense.  Let us collect new data to see what is going on

Cheers, Igor

On Mon, 24 May 010 17:33:50 -0400 (EDT), Volker Crede 
<crede at hadron.physics.fsu.edu> wrote:

> Hi all,
> 
> last Wednesday in the FROST meeting, we started discussing the possible 
>physics case for a short, three-week long FROST run for measurements off the 
>neutron using deuterized butanol. In my opinion, the most interesting physics 
>topic to advertize would be the study of the 1650-1700 MeV mass region in eta 
>photoproduction. Using a linearly-polarized beam at 1.1 GeV coherent edge 
>position would be ideal; in combination with transverse target polarization, 
>the observables H and P can be measured.
> 
> The reason why this interesting is the relatively narrow structure that has 
>been observed at 1680 MeV off neutrons bound in the deuteron at:
> 
> * GRAAL (width < 30 MeV): Kuznetsov et al., Phys. Lett. B647 (2007) 172.
> * ELSA (width < 60 MeV): I. Jaegle et al., PRL 100 (2008) 252002.
> * MAMI (width about < 40 MeV): not yet published
> * Tohoku-LNS (width < 40 MeV):
>    F. Miyahara et al., Prog. Theor. Physics Supplement 168 (2007) 90.
> 
> A pronounced bump appears in the total cross section. Although the nucleon 
>resonance, D15(1675), is not a likely cause of the narrow structure, it's 
>role in this reaction is not entirely understood; it cannot be ruled out that 
>significant contributions from this state in addition to the narrow structure 
>cause the much slower fall-off of the neutron cross section in this energy 
>region compared to the proton. I have attached a picture with sensitivity 
>studies on the D15(1675) using MAID at 1 GeV. The solid, red curves indicate 
>the full model; the dashed, blue curves without D15(1675). The model predicts 
>asymmetries of measurable size for basically all pol. observables. The cross 
>section data are from ELSA, the beam asymmetry was measured at GRAAL.
> 
> Taking data for all other reactions simultaneously is certainly also useful, 
>but since we have only three weeks, I think eta photoproduction offers this 
>particular physics case. A dedicated run at 1.1 GeV for both transverse 
>target polarizations (to get H and P) would be very useful.
> 
> What do you think?
> 
>    Volker

Igor Strakovsky, SAID CNS The George Washington University
Tel: 703-726-8344(NV),202-994-4742(FB),Skype: igors1945_2
Fax: 202-994-3001(FB),Emails: igor at va.gwu.edu, igor at jlab.org