[E12-11-009-collab] Talks from Feb 15 Collaboration Meeting

[Brad Sawatzky]

You can find the talks from our recent collaboration meeting here:
  https://hallcweb.jlab.org/doc-public/DisplayMeeting?conferenceid=27


Bryon Anderson made an nice synopsis of the meeting (below):

Michael Kohl presented John Arrington's review of the scientific
motivation for the experiment.  Michael added a few slides at the
beginning to indicate some of his previous experience on this kind of
experiment and to add to the description of the motivation.

Andrei Semenov then made his presentation showing his Plan A and Plan
B geometries for the neutron polarimeter.  These Plans were
distributed by Andrei to the spokespersons a week or two ago.  Andrei
presented a very nice update on the expected A.P. for n-p scatterring
obtained, as I understand it, from discussions and references obtained
from persons at Dubna.  He broke the discussion of A.P. up into n-p
elastic, n-p quasielastic on C and inelastic.  He showed n-p elastic
A.P. angular distributions for a few relevant momentum transfers.
These show that the A.P. is positive, typically 10 to 15 % from around
5 to 10 degrees of neuton scattering angles. At larger angles, it
sometimes goes negative, so one needs to have good angular resolution.
 From all this info, Andrei showed that we need to do all that we can
to help with count rate and FOM.  This led to his Plan A and Plan B
proposed geometries.  Andrei showed that even with the improved
geometry, because of the new information on the A.P., the FOM for the
highest Q**2 is reduced somewhat from that presented to the PAC.

Much discussion followed Andrei's presentation.  There was general
agreement that something like what he was proposing was required,
although the geometry of the "up" and "down" detectors appears
difficult.  Michael Kohl noted that there are a no. of 10 cm X 10 cm X
4 m detectors at MIT Bates that were used in BLAST that might be able
to be used for the up and down detectors.  It was agreed that this
should be seriously considered.

After lunch, I (B. Anderson) presented a talk reviewing the present
status of available neutron and veto detectors, and needs for
front-end electronics.  Between available detectors now in the Hall A
HAND detector, which includes all the 10 x 10 x 100 cm front detectors
from our earlier GEn experiment in Hall C, plus a no. of 5 X 4 X 40 in
detectors that belong to KSU, plus possibly using the 10 x 10 x 160 cm
detectors from the Hall A GEn experiment as suggested by Donal Day,
that we would have enough neutron detectors to assemble the
polarimeter proposed to the PAC.  In order to implement new Plan A or
B, considerable work would need to be done, probably using the Hall A
160 cm detectors, which may or may not be allowed.  In the discussion,
it was agreed again that using the 4 m detectors from BLAST may be the
best solution.

The veto detector situation is not well known.  Perhaps one-half of
those needed exist at JLab.  Considerable work needs to be done here.
In private conversation later, Abdellah Ahmidouch from NC AT&T Univ.,
indicated that his group could take the lead in responsibility  for
veto detectors.

For front-end electronics, it was discussed that we probably can get
the kind of timing we need from Flash ADC's, or some system without
having to use CR discriminators in the Hall.  So many detectors are
planned now, that we do not have one-half of the CF's that would de
needed and this would cost around $100K, or more.  Brad Sawatsky
thinks that we can probably make this work. Much discussion followed
about this and about count rates and maintaining stable detector gains
in the scatterer detectors.

After coffee, Brad Sawatsky made and excellent presentation about
possible DAQ systems and software needs.  Several systems are
available, one or more of which will probably work for this
experiment.  Accurate count rate estimates for the various detectors
are needed to make final decisions.

A general discussion followed Brad's talk, discussing such things as
target cryo power needs, beam polarization measurements (Moeller and
Compton), detector stands and shielding, electron-arm electronics,
etc.  The strong need for a precessing, sweeping magnet(s) was
discussed several times during the day and this remains a large
concern.

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-- Brad