[Clas12_rgb] [EXTERNAL] Re: feedback needed on Beam Energy Requirements in Hall B

[harut avagyan]

Hi Silvia,
What I sent to Latifa to address the same questions is very close to your
comments.
(b) 10.55 -10.6GeV  to be consistent with what we collected so far, in
particular with RGC to avoid unnecessary work. We will, however, prefer the
stable beam versus higher energy unstable.
(c) a reduction of beam energy impacts mainly the maximum Q^2 (relevant for
evolution studies) and P_T (relevant for studies of transverse momentum,
higher cleaner from rho) for SIDIS
experiments.
(d) running longer helps, as smaller kinematic range will be compensated
 to some extent with higher  statistical precisions in accessible
kinematics.

Best,
Harut

On Mon, Aug 5, 2024 at 12:42 PM Silvia Niccolai via Clas12_rgb <
clas12_rgb at jlab.org> wrote:

> Dear all,
> a few days ago I received the email, that I report at the end of my
> message, from Patrick.
> Here is my first-draft proposition, for the table that Patrick requests,
> for RGB:
>
> (a) 11 GeV
> (b) 10.6 GeV (it is the maximum energy we had so far for RGB) - or should
> we put 10.7 to be consistent with the current expectations for Hall B
> reported in Patrick's message?
> (c) a reduction of beam energy impacts mainly the nDVCS, Gmn, and J/psi
> experiments, as it reduces the kinematic reach in not-yet-explored
> regions. Measuring DVCS at highest-possible Q2, in particular, is crucial
> to ensure applicability of the leading-twist formalism for GPDs.
> (d) running longer can help increase the statistics in the
> statistics-starved kinematics at high Q2, where the cross section drops.
>
> Can you please give me your feedback on this table, as soon as possible?
> Please reply directly to the mailing list.
> Thanks a lot and best regards,
> Silvia
>
>
> Dear contact persons of '11-GeV runs' in Hall-B,
>
> Earlier this year, DOE has performed an Operations Review which was
> concluded with a list of comments and recommendations. One particular
> recommendation is to... "Develop a beam energy requirement document for
> the approved experiments in the experimental halls, complete with physics
> justifications. This document must be distinctly separate from issues
> pertaining to reliability."
>
> Physics division will compile, for each experiment still to run, (a)
> Proposed Energies, (b) Minimum Acceptable Maximum Energy if 12 GeV was
> proposed, (c) Science Impact of difference from 12 GeV, and (d) any
> potential mitigation such as run longer.
>
> The focus of this recommendation is a review/justification for a 12-GeV
> CEBAF beam (equiv. to 11 GeV delivered to Hall B) as compared to a beam
> with some 100s MeV less energy.
>
> Can you please give me input to the requested table entries (a) to (d)?
> Feel free to justify running at 11 GeV for Hall B with some extra
> narrative if the table is not sufficient. I believe, we can give common
> numbers for experiments in run groups for which the science impact and the
> potential mitigation is similar. However, I don't think that we can
> combine all experiments from a run group.
>
> Let me remind you, the scheduled beam energy for the next run is 1060 MeV
> per linac, equiv. to 10.70 GeV in Hall B. Plans are in place to increase
> this to 1090 MeV, equiv. to 11 GeV in Hall B for the FY26, but not at all
> cost.
>
> Physics division is not moving quickly on this, so a reasonable target to
> have all information compiled is August 20, 2024.
>
> Best regards,
> Patrick
>
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