[Frost] Neutron Measurements with FROST

[Volker Crede]

Igor,

the D15(1675) resonance was just an idea; it's most likely not the reason 
for the narrow structure, but probably contributing in this mass range. 
The picture I sent out is actually from an internal CBELSA/TAPS note and 
has been the basis for some discussion about this narrow structure.

The MAMI data I mentioned have not been published, yet. I also have not 
seen anything. Bernd Krusche told me about it (private communication); if 
I remember correctly he has a student working on this.

Whatever the details, I think this is what we should do.

     Volker


On Mon, 24 May 2010, Igor Strakovsky wrote:

> 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
>