[Clas_cascades] Minutes 9/9/2010

[Zhiwen Zhao]

On 09/03/2010 11:31 AM, Igor Strakovsky wrote:
> Dear Zhiwen,
>
> I have several questions to you...
>
> 1) I am a little bit confused - what is the purpose of your analysis? In
> particular, you pretend to compare with the LEPS experiment. But your
> plots show that you have practically no statistics below 20 deg. This is
> especially so for "on Lambda(1520)", where interference amplification
> could be expected.
The purpose of the study is search for Theta+ production on neutron by 
detecting all particles pK0Km except the spectator proton. This not a
direct comparison to LEPS result because they are looking at a different 
decay channel nKpKm. If you believe Theta+ may decay into pk0 and nKp at 
the same time, you should assume this study is meaningful.
And I believe this channel actually has some advantage because we can 
study exclusive reaction, while the channel LEPS used depends on some 
models and they could be questionable ( see the paper pointed out by 
Eugene here http://arxiv.org/abs/1008.4978 ). I heard LEPS is looking 
into the same channel and I don't know what's their outcome yet.
I have some slides in the talk I gave last year about the background info.
http://www.jlab.org/Hall-B/secure/hadron/meetings/19mar10/hadron20100319_zwzhao_Lambda1520Theta+.pdf

So again this's not a direct comparison to LEPS result, but a search for 
the same physics. Therefore, some of conditions and cuts LEPS used could 
be borrowed to see what we have.
For my understanding, LEPS didn't cut out Lambda1520, but their Theta+ 
signal is well separated from Theta+, see the Fig 12(b) in their 2009 
paper here 
http://clasweb.jlab.org/rungroups/eg3/wiki/images/f/f4/PhysRevC.79.025210.pdf
We can decide to cut on Lambda1520 away or not, but in the plots, I 
shows them all.

> BTW, Takashi Nakano told me that he tried to change his setting so to
> reproduce CLAS conditions, and it does not work for him.
This is a very interesting comment. As you know, LEPS have very 
different coverage from common CLAS setting. They have the very forward 
angle detector which CLAS only can do with negative field. eg3 is the 
only run so far has the potential to have some overlap with LEPS 
coverage. I am curious about what did not work for him.
>
> 2) Then, is it possible to see your Ks recoil spectrum? Its structure,
> with well known Sigma and Lambda states, would allow to estimare how
> good your selected pi+pi- pairs correspond to K0 decay products.
Lambda1520 production study is not completed yet, but in good shape. I 
used pkm invariant mass for the study, not xk0 because it's not a free 
target. but the K0 invariant mass plot can be seen at the same wiki page 
and in my talks. However I have to study its large background more 
carefully.
>
> 3) As far as I can see, your collinear cut is cos(theta)>0.9 while the
> ODU analysis demonstrated thar the optimal boundary is 0.98, and
> definitely not less than 0.95. Can you do such cut?
I can try to do a tighter cut, but I won't be left with good stat 
because its an elusive reaction while ODU study is inclusive. And again 
this related to K0 background which I have to deal more carefully,

>
> 4) For the pK-Ks events you show us the spectra M(pKs). But the ODU
> analysis has demonstrated that such spectra have a bad resolution,
> because of proton measurements in CLAS. Could you show instead the
> spectra of MM(K-)?
I have to study the resolution issue also the background from k0. but I 
doubt MM(K-) will really help me because the D target. Anyway, I will 
check it.
>
>
> Elton,
>
> Recently, your committee accused the ODU analysis for using a t-cut. Now
> your suggestion to Zhiwen is to do just the t-cut. Have you changed your
> mind?
>
> Thanks, Igor
>
>
> On Thu, 2 Sep 2010 09:29:21 -0400 (EDT), Elton Smith <elton at jlab.org>
> wrote:
>
>>
>> Present: Elton, Hovanes, Zhiwen, Kijun, Stepan
>> On the phone: Ralf <br>
>> Notes by Elton.
>>
>> == Announcements==
>> # Hovanes will run the next meeting, 8:00 am Sep 9
>>
>> == Draft of Phi-- Paper (Hovanes) ==
>> # Started including sections of the analysis note and submitted to cvs,
>> but not yet ready for other input
>> # There will be quite a long sections included, but they can then be cut
>> back
>> # Asked whether there should be discussions of two sets of cuts (liberal
>> and conservative): Elton: Focus on the set of cuts used for the upper
>> limit. It makes the paper simpler and easier to read.
>> # Stepan: Compare results to normal cascade cross sections
>>
>> == Theta+ (Zhiwen) ==
>> # Started looking at g n -> K-K0p(p), with Theta+ -> K0p.
>> # Advantages of eg3 are better acceptance for K- in forward direction,
>> and
>> larger overlap with LEPS kinematics compared to other CLAS analyses
>> # Invariant mass plots of (K0p) shown. No indication of a peak in the
>> region close to 1530-1540.
>> # Stepan: list of cuts to consider are a) Missing mass peak b) photon
>> energy cuts c) t-cuts.
>> # Elton: Suggests to only use missing mass cut for primary mass spectrum,
>> and use t-ranges as a selection only to compare to LEPS data.
>> # Elton: Try to get an estimate of an upper limit to see if it is
>> competitive with LEPS published results.
>>
>> == Next Meeting Sep 9, 8:00 am ==
>> # Phi-- Draft of paper (Hovanes)
>> # Theta+ update (Zhiwen)
>> # Analysis note for Lambda(1520)?
>>
>>
>> Elton Smith
>> Jefferson Lab MS 12H5
>> 12000 Jefferson Ave
>> Suite # 16
>> Newport News, VA 23606
>> elton at jlab.org
>> (757) 269-7625
>> (757) 269-6331 fax
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>
> 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