[Frost] Neutron Measurements with FROST

[Philip L. Cole]

Hi all,

Are there any plans to use the LAC for detecting neutrons?  Right now, ISU
is working on calibrating the LAC for g13 and I wonder if it would be
useful for the deuterated butanol target for FROST.

Phil

> Barry, let me clarify physics (experimental part is hard, no questions).
>
> First of all, the structure in the cross section of the gn-->etaN at W =
> 1680 MeV has been observed by three (correctly four as Volker pointed out)
> groups independently.  The cross section on the neutron is larger than on
> the proton by a factor of 7 (for the P11 case, u-spin can explain this
> large factor).  Sigma-beam asymmetry changes a sign at the same place.
> That is not a hunting for a bump.  Something is going on here and it is
> good to figure out what is going on
>
> Mike, if our feeling is correct and we met a non-strange narrow resonance
> (say 20-40 MeV) that is something.  We do not know any so narrow and
> non-strange baryons.
>
> Pi-p case is bad for the P11 (BR P11 into pi-p is too small) but we found
> a suspect via piN modified PWA.  So, there is a chance that polarized
> measurements will allow to catch up something
>
> Igor
>
> On Mon, 24 May 2010 22:47:02 -0400 (EDT), Michael Dugger <dugger at jlab.org>
> wrote:
>
>>
>> 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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-- 
   Philip L. Cole
   Associate Professor
   Idaho State University
   Department of Physics
   Pocatello, Idaho 83209
   (208) 282-5799  office
            -4649  fax
    cole at athena.physics.isu.edu
    http://www.physics.isu.edu/staff/cole.html