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<p>Dear Volker,</p>
<p>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.)</p>
<p> Kind regards,</p>
<p>Maxime<br>
</p>
<div class="moz-cite-prefix">On 25/10/2018 19:37, Francois-Xavier
Girod wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAOKxh47rq+O8jw_kwW0Vzmumuz0f3HZEeGoGvm_eNyNWYy6UHg@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Dear Volker
<div><br>
</div>
<div>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. </div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>Best regards</div>
<div>FX</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Thu, Oct 25, 2018 at 1:15 PM burkert <<a
href="mailto:burkert@jlab.org" moz-do-not-send="true">burkert@jlab.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div class="m_3725191116230764221moz-cite-prefix">All,<br>
<br>
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. <br>
<br>
Typo: In the next to last paragraph please delete the
first "during" in the string " <span> during as soon as
possible during the November RG..</span> <br>
<br>
Regards,<br>
Volker<br>
<br>
<br>
On 10/25/18 7:41 AM, Annalisa D'Angelo wrote:<br>
</div>
<blockquote type="cite">Dear All, <br>
<br>
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: <br>
<br>
<a class="m_3725191116230764221moz-txt-link-freetext"
href="https://userweb.jlab.org/~annalisa/hybrid_baryons/RGK_response_to_CCC.docx"
target="_blank" moz-do-not-send="true">https://userweb.jlab.org/~annalisa/hybrid_baryons/RGK_response_to_CCC.docx</a>
<br>
<br>
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. <br>
<br>
This would optimize the overall efficiency. <br>
<br>
Please let me know your opinion on the matter. <br>
<br>
Any comment/correction/suggestion is highly appreciated <br>
<br>
All the best <br>
<br>
Annalisa <br>
<br>
p.s. we may discuss the matter tomorrow at the RGK weekly
meeting. <br>
<br>
<br>
</blockquote>
<p><br>
</p>
</div>
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