[Clas_cascades] eg3 data analysis

[Igor Strakovsky]

Dear Ralf,

Let me answer you (see below...)

> Igor Strakovsky wrote:

>> Dear Ralf,
>>
>> Thank you for your writing me. I admit that my questions addressed to
>> Zhiwen gave him some troubles. And now I can hear a senior reaction.
>>
>> On Thu, 16 Sep 2010 10:45:27 -0400, Ralf W Gothe <gothe at physics.sc.edu>
>> wrote:
>>
>>> Dear Igor,
>>>
>>> we are in the process of identifying the statistical significance of
>>> our results, as well as we are still playing with all - more or less -
>>> reasonable cuts. We haven't even produced an analysis note let alone
>>> a paper draft on this topic. Hence criticizing cut conditions as well
>>> as other claims that have not been finalized still doesn't make too
>>> much sense. Of course, suggestions to optimize cuts and/or the analysis
>>> are always welcomed but best placed if we could discuss them with you
>>> in our weekly meetings, where you could also learn more about issues
>>> we already have discussed.

>> I would like to play as well. Therefore I am curious to see a KS plot
>> which I asked Zhiwen to do. I cannot understand why Zhiwen (or you)
>> could not show me that.

> As Zhiwen already pointed out to you, you may find it on our wiki page
> or in his slides e.g.
> http://www.jlab.org/Hall-B/secure/hadron/meetings/19mar10/hadron20100319_zwzhao_Lambda1520Theta+.pdf

I've looked through Zhiwen's slides, but I could not find a picture that
I asked Zhiwen to show me. If you mean a particular slide, please let
me know which one.

BTW, the slide of p21 gives a very intriguing picture. It shows data and
simulation for the proton momentum distribution. They exactly coincide at
P<0.2 GeV/c(?), where direct detection of protons in CLAS is technically
impossible. However, in the whole region P>0.2 GeV/c, where the direct
detection is possible, the data and simulation are strongly different,
up to 10 times or even more.

Could you please explain why the boundary between good and bad agreement
of data and simulation is just the lowest detected momentum?

>> Regarding cuts...  As far as I know, recently Elton's committee accused
>> the ODU analysis for using a t-cut. Now Elton's suggestion to Zhiwen is
>> to do just the t-cut. Because Elton does not answer my simple and naive
>> question - can you do that for Elton?

> t and theta cuts are not independent and impact potentially the physics.
> We just want to see how.

You are right, and in the ODU analysis they also studied correlations
between t and other variables. But I would like to understand why Elton
suggests you to use the t cut for his eg3, while he strongly opposed its
use in the ODU analysis. What could be the difference?

Of course, I guess that you are not responsible for Elton, and nevertheless...

>> And one more... Hovanes minutes (Sept 9th) gave estimation of the
>> Theta+ production from eg3 as 10 nb.  Can I ask you please how strong
>> was this point?  I do not think that the 10 nb limit is publishable.
>> BTW, on the proton or neutron?

> Very vague!

OK, I see your position.

>>> One last remark, we clearly cannot unambiguously state that we have
>>> measured the production off a free proton, but we can determine the
>>> so-called spectator-proton momentum even below 200 MeV/c.

>> Sure, because of the deuteron target, eg3 does not allow a free proton
>> measurement.  But if you recover a 'spectator-proton' (CLAS cannot
>> explicitly measure outcoming protons with momentum less than 200 MeV/c,
>> but could find slower protons by missing mass) then you can consider a
>> neutron as target.  The question is - how small is your lowest proton
>> momentum?  Can you reach the regime where impulse approximation would
>> be applicable?

> Again you may find it on our wiki page or in his slides e.g. (slide 21)
> http://www.jlab.org/Hall-B/secure/hadron/meetings/19mar10/hadron20100319_zwzhao_Lambda1520Theta+.pdf

OK, one question on just this slide 21 was formulated above. Here is one
more question. The slide shows the proton momentum distribution in the
log scale.

Is it possible to see a linear scale for P<250 MeV/c or so?

BTW, if you are going to use impulse approximation (spectator mechanism),
you have to keep your cut on the level P<50 MeV/c (average momentum of
the nucleon in the deuteron), not P<200 MeV/c.

And an additional question. For me, the missing proton mass distributions
(p20} look too broad. It means for me that your proton momentum recovery
might be not sufficiently good.

Best, Igor

>> Kind Regards,
>> Igor
>>
>>> Best regards,
>>>
>>> Ralf