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

[mdefurne]

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 
> <mailto: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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