[Frost] Neutron Measurements with FROST

[Barry Ritchie]

As I've often said, I'm not a big fan of bump-hunting anyway, but this
strikes me as very, very dicey motivation. Note that just finding a
reasonable signal for photoproduction on the proton using FROST has been
incredibly difficult because the target backgrounds are relatively
ENORMOUS. Any event signature restrictions just makes the miniscule peak
even smaller. I don't know whether Brian has anything up more recently,
but I recall what he was getting in March:
http://www.jlab.org/Hall-B/secure/g9/morrison/eta_scheme_tests/eta_schem
e_testing.html 

The only thing we're likely seeing there is threshold photoproduction
near 800 MeV. Up where you guys are talking about, the peak is probably
not visible at this time. 

The neutron cross sections will be between factors of 5 to 10 lower than
the proton cross sections, if we are to believe the GRAAL numbers. So,
I'm not optimistic at all that looking for eta photoproduction on the
neutron using FROST is going to be feasible. 

And, whatever the decision, you absolutely cannot break up a few-week
run period and hope to see anything at all.
 

---BGR

Professor  Barry G. Ritchie 
Department of Physics 
Arizona State University 
Tempe, AZ  85287-1504 
  
Telephone: (480) 965-4707 
Fax: (480) 965-7954 

-----Original Message-----
From: frost-bounces at jlab.org [mailto:frost-bounces at jlab.org] On Behalf
Of Volker Crede
Sent: Monday, May 24, 2010 4:32 PM
To: Igor Strakovsky
Cc: FROST
Subject: Re: [Frost] Neutron Measurements with FROST

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
>
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