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

[Francois-Xavier Girod]

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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>
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