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

[silvia at jlab.org]

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