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

[burkert]

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 
>> <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
>>>     <https://userweb.jlab.org/%7Eannalisa/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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