[Frost] Neutron Measurements with FROST

[Michael Dugger]

Just to clarify something that I think Eugene forgot to mention: The pi- 
on the neutron probably won't show the bump. The physics motivation is 
different. The good part is that we should be able to get this channel 
easily. The bad part is that the physics motivation is not as strong.

-Michael

On Mon, 24 May 2010, Eugene Pasyuk wrote:

> Eta-production on the neutron is hardly possible with FROST or even
> HDIce for that matter. I looked in to that when HDIce proposal was
> written. One would need to detect two charged pions, two photons from
> pi0 decay and a neutron. The acceptance is way below 10^-3, more like
> 10^-4. That's on the top of a large background. Acceptance of CLAS to
> 2gamma decay of eta is tiny as well. This case is even worth, no charged
> particles in final state at all! That's ok for detectors like Crystal
> Ball or Crystal Barrel, but not for CLAS.
> What seems to be doable is K0Lambda on the neutron. This is four charged
> particles final state.
> And of course pi- on the neutron.
>
> -Eugene
>
> On 5/24/10 5:33 PM, Volker Crede 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
>>
>>
>>
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