[clas12_rgk] draft of response letter to CCC from run group K

Fri Oct 26 19:04:55 EDT 2018

Dear Volker

I completely agree with this suggestion. We did some tests in the past with
event by event likelihood. Assigning negative likelihood to background
events we were able to cross check asymmetries. It would be even better to
do this at the level of amplitudes and CFFs. This is not something that can
be demonstrated in a couple days however. It will requires time to move in
this direction.

Nevertheless, even with the best possible analysis, it still remains true
that combining short amounts of data taken months or years apart will be
detrimental to our systematics. During our PAC presentation we were
challenged in our supposed aggressive estimation of systematics, on the
basis of the published systematics from e1dvcs. It was always clear to me
that we should aim to improve the systematics we had in the past, and I
think we have reasons to believe we can do so. This public challenge in
front of the PAC from the very people in charge of scheduling now puts us
naturally in a position to be reluctant to agree to increased systematics.
Our proposal already has the most challenging analysis of the approved
exclusive program. I think our proposal deserves to be scheduled in full
and not as convenience to fill in between other experiments.

Best regards
FX

On Fri, Oct 26, 2018 at 6:42 PM burkert <burkert at jlab.org> wrote:

> Hi Maxime,
>
> I can understand that if we keep working with binned data sets that
> changing the energy can create such issues. However, is this the way we
> want to continue, instead of moving towards non-binned data analysis, which
> I think will not have these same issues and allows more flexibility in the
> final physics analysis? We should explore this possibility more.
>
> Volker
>
>
>
>  On 10/26/18 12:03 PM, mdefurne wrote:
>
> Dear Volker,
>
> I completely agree with F-X about the recommendation of keeping the beam
> energy as stable as possible. And I agree that combining this two "data
> set" might significantly increase the systematics. This kind of exercise is
> extremely complicated and the final results tends to be extremely sensitive
> to the overall systematics. (You can trust me on this for having done it in
> Hall A and it was with a much simpler experimental setup.)
>
>   Kind regards,
>
> Maxime
> On 25/10/2018 19:37, Francois-Xavier Girod wrote:
>
> Dear Volker
>
> The DVCS group has some experience combining datasets at 6.75 and 6.88
> GeV. It does actually require caution and should be evaluated carefully
> before stating that we can accept such differences of 100 MeV or more. The
> issue is not simply that the cross-section changes, which can affect the
> real part of the amplitude, but the issue is also that the kinematics
> change. Q2 is not the same in xB and theta bins. Of course we can attempt
> to correct for this by changing the binning in theta to keep Q2 fixed, but
> then we also change xB... And in the end, even if we somehow manage to keep
> xB and Q2 both fixed, we will still have a change in epsilon which enters
> the Rosenbluth separation when combining beam enegies.
>
> In writing our proposal we do not have strong constraints on the absolute
> beam energy, but we do have an expectation that the energy will be fixed at
> better than the MeV level. Combining beam energies as far as 100 MeV will
> for certain affect our systematical uncertainties. If we really have to
> work with this, then we must do our homework and put a number on this. I do
> not think it is a straightforward exercise however.
>
> Best regards
> FX
>
> On Thu, Oct 25, 2018 at 1:15 PM burkert <burkert at jlab.org> wrote:
>
>> All,
>>
>> I agree with intention of the text. However, I suggest to downplay the
>> 6.5 vs 6.4 GeV. I don't think it is such a big deal and we have to deal
>> with that later again as the machine energy will never be exactly the same
>> as in previous run periods. We have to learn how to deal with slight energy
>> variations in an effective way.
>>
>> Typo: In the next to last paragraph please delete the first "during" in
>> the string " during as soon as possible during the November RG..
>>
>> Regards,
>> Volker
>>
>>
>> On 10/25/18 7:41 AM, Annalisa D'Angelo wrote:
>>
>> Dear All,
>>
>> after last RGK meeting, some additional  thinking and exchange of
>> information with Raffaella, I have put together a draft letter to answer
>> the CCC request information, which you may find at:
>>
>> https://userweb.jlab.org/~annalisa/hybrid_baryons/RGK_response_to_CCC.docx
>>
>> In a nut shell I would like to propose that the new trigger requiring a
>> central hadron could be implemented and commissioned as soon as possible
>> during RGA, not to loose time during our assigned RGK data taking. RGA
>> could take all the Spring data taking in return.
>>
>> This would optimize the overall efficiency.
>>
>> Please let me know your opinion on the matter.
>>
>> Any comment/correction/suggestion is highly appreciated
>>
>> All the best
>>
>> Annalisa
>>
>> p.s. we  may discuss the matter tomorrow at the RGK weekly meeting.
>>
>>
>>
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