[Gdh_lowq2] EG4 meeting

Tue Feb 18 22:50:29 EST 2014

In my analysis, I have two cases: one like yours (neutron only
"detected" by missing mass); and one in which I actually detect
a neutron in the EC (a neutral particle with beta<0.95). In this
case, I can put cuts on the angle between predicted and measured
neutron direction cosines, which can eliminate almost all of
the ammonia events if made sufficiently tight. As far as I know,
I'm the only one doing this second topology. It works best for
the higher neutron momenta, where the detection efficiency is greater.
Peter

> I did apply a cut on the neutron peak in the missing mass spectrum.
>
> Xiaochao
>
> ----- Original Message -----
> From: "Sebastian Kuhn" <kuhn at jlab.org>
> To: bosted at jlab.org
> Cc: "Xiaochao Zheng" <xiaochao at jlab.org>, "gdh lowq2" <gdh_lowq2 at jlab.org>
> Sent: Tuesday, February 18, 2014 2:48:31 PM
> Subject: Re: [Gdh_lowq2] EG4 meeting
>
> I may be wrong, but I thought Xiaochao's analysis does NOT include
> detection of the neutron in the pi+ case. Then, you otherwise valid
> exclusivity argument is not quite as convincing - you may get a reasonably
> good measurement at the 20% level, but not as good as the dedicated Ae
> measurements Volker mentions.
>
> - Sebastian
>
> On Feb 18, 2014, at 2:12 PM, bosted at jlab.org wrote:
>
>> Hi all,
>>   Yes, there is some mixture in our measurement of Ae from
>> A>2 nuclei like nitrogen. But, in the fully exclusive
>> topologies, like e p -> e pi+ n (all particles detected),
>> the exclusivity cuts reduce the A>2 contribution to a very
>> small level (less than 10% for eg1-dvcs), due to the ability
>> to cut on the neutron angle relative to that expected for
>> a stationary target. Similarly for pi0 with the proton and
>> both pi0 decay photons detected.
>>   If CLAS had published Ae for exclusive pion production
>> already, then it would be interesting to compare with
>> pure proton results. However, as far as I can tell, almost
>> nothing is published. If there are results for Ae
>> for exclusive pi+ and/or pi0, can somebody please give
>> me the references? In fact, the eg1-dvcs Exclusive Analysis
>> Note Review committee asked for such a comparison, so
>> I am vitally interested!
>>   Yours, Peter
>>
>>
>>> Hi Xiaochao,
>>>
>>> thanks for the update. I know that Peter is always interested in Ae -
>>> I'm
>>> a bit puzzled by that. As you know, what we measure in experiments like
>>> EG4 is a rather haphazard average of Ae on a mix of proton, Helium,
>>> Nitrogen and other elements. As a rough check (does it agree with
>>> precision data on the proton alone) it may be useful (especially for
>>> pi+
>>> which will be totally dominated by protons). So, I agree, the
>>> EXPERIMENTAL
>>> systematic uncertainty is small (no dilution factor or Pt needed), but
>>> I'm
>>> not sure what one can really learn.
>>>
>>> - Sebastian
>>>
>>> On Feb 18, 2014, at 2:06 AM, Xiaochao Zheng <xiaochao at jlab.org> wrote:
>>>
>>>> Dear Alexandre and all:
>>>>
>>>> Just another weekly update:
>>>>
>>>> My student has converted all exclusive pi+/NH3 ntuple results to plain
>>>> text files. I emailed these files to both Igor and Peter.  Peter has
>>>> made some plots on the 3 GeV data. I believe he is looking at other
>>>> energies right now. And we will keep discussing about the plots.
>>>>
>>>> Igor is taking shifts at Mainz and he said he will look at the data
>>>> carefully when he comes back. He mentioned that if we need to combine
>>>> bins to get higher statistics, he prefer that I do it, so that the
>>>> combining process can be done properly.
>>>>
>>>> Both Igor and Peter have expressed interest in the single-beam
>>>> asymmetry
>>>> Ae. I didn't expect this, and need to look at the systematic
>>>> uncertainty
>>>> of Ae carefully. At the first thought, the uncertainty of Ae should
>>>> come
>>>> only from the beam polarization, which would be from Moller alone. At
>>>> the moment I am taking a simple average of the Moller error bars (for
>>>> example if there are two Moller results during the 3GeV run period, I
>>>> am
>>>> taking the average of the two relative Moller uncertainties).  If
>>>> Moller
>>>> is indeed the only dominate error for Ae, then I plan to calculate the
>>>> statistics-averaged value from multiple Moller measurement.  Please
>>>> comment.
>>>>
>>>> If eventually Ae is provided as results from EG4, should I add these
>>>> to
>>>> the analysis note too?
>>>>
>>>> I also found I have misused the uncertainty of (f*Pb*Pt), with f the
>>>> dilution factor, as the systematic uncertainty for both Aet and At.
>>>> The
>>>> correct way should be to use the error of (f*Pb*Pt) for Aet alone. For
>>>> At, the uncertainty should come from (f*Pt), not Pb. But since the
>>>> elastic analysis provides the product of Pb*Pt, the correct way for At
>>>> would be to add the relative uncertainty of Pb (Moller) to that of
>>>> (f*Pb*Pt) in quadrature, to get a conservative estimate of the
>>>> systematic uncertainty for (f*Pt) for At. The resulting relative
>>>> uncertainty isn't too much higher than that of Aet because Moller
>>>> typically have <2% of relative uncertainty.
>>>>
>>>> I will keep everyone posted on the progress. Thanks,
>>>>
>>>> Xiaochao
>>>>
>>>> ----- Original Message -----
>>>> From: "Xiaochao Zheng" <xiaochao at jlab.org>
>>>> To: "Alexandre Deur" <deurpam at jlab.org>
>>>> Cc: "gdh lowq2" <gdh_lowq2 at jlab.org>
>>>> Sent: Monday, January 27, 2014 3:07:13 PM
>>>> Subject: Re: [Gdh_lowq2] EG4 meeting
>>>>
>>>> Dear Alexandre and all:
>>>>
>>>> I am never able to attend this meeting so it might help to provide an
>>>> update on the exclusive analysis by email:
>>>>
>>>> As some of you know, we received the review on our analysis note last
>>>> fall. Reading through the review, the major concern is what physics
>>>> conclusion can we draw from these results?  I discussed this with the
>>>> exclusive group and we think the best way is to send the results to
>>>> Igor
>>>> and have him look at it. He will be able to compare the new data with
>>>> all existing ones and come up with ideas.
>>>>
>>>> Igor requested the data in plain text form, while my data were stored
>>>> in
>>>> ntuples.  I asked one of my 2nd-year students to work on the format
>>>> conversion. It has been about two weeks and he has been making some
>>>> progress. Once he completes for one kinematics, I will do a cross
>>>> check
>>>> and send the plain-text data to Igor, and we will proceed from there.
>>>>
>>>> Thanks for your attention.
>>>>
>>>> Xiaochao
>>>>
>>>> PS is today already Jan. 28th?
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: "Alexandre Deur" <deurpam at jlab.org>
>>>> To: "gdh lowq2" <gdh_lowq2 at jlab.org>
>>>> Sent: Monday, January 27, 2014 1:33:57 PM
>>>> Subject: [Gdh_lowq2] EG4 meeting
>>>>
>>>> Dear EG4 collaborator,
>>>>
>>>> We will have our EG4 analysis meeting today (Jan 28th) at
>>>> 9:30am (EST) in room F227. Instructions to call-in can be found at:
>>>>
>>>> http://www.jlab.org/Hall-B/secure/eg4/deur/call_in_procedure.html
>>>>
>>>> Best regards,
>>>>
>>>> Alexandre
>>>> _______________________________________________
>>>> Gdh_lowq2 mailing list
>>>> Gdh_lowq2 at jlab.org
>>>> https://mailman.jlab.org/mailman/listinfo/gdh_lowq2
>>>> _______________________________________________
>>>> Gdh_lowq2 mailing list
>>>> Gdh_lowq2 at jlab.org
>>>> https://mailman.jlab.org/mailman/listinfo/gdh_lowq2
>>>
>>>
>>> _______________________________________________
>>> Gdh_lowq2 mailing list
>>> Gdh_lowq2 at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/gdh_lowq2
>>>
>>
>>
>