[Halla_parity] PREX status

[Robert Michaels]

Dear Colleagues

The PREX experiment is on the verge of going into
production data-taking after a successful but
slightly slow start.  The commissioning has been
very successful.  The high-current data on lead
show we can meet our statistical goals; the noise
and beam systematics appear to be, in first analysis,
excellent.  Of course, we need a few more days of
production and a fully-debugged analysis chain to
be 100% sure.

We measured our vertical spin asymmetry; I can't
tell the results here but it was "very encouraging". 
If you've been to the hall A meetings you've heard
that the upgraded Moller and Compton polarimeters
are working and now need to do studies to understand
the systematics at the ~1% level; they will get
priority for this.

At the moment there is a vacuum problem in the
target chamber; possibly a leak, but not it's not
really known.  The target group is investigating.
Swing (Apr 6) and Owl (Apr 7) are on "standby" --
meaning you don't need to come in.  The target is
warm and we're in restricted access.  But keep
you pager handy.  The Run Coordinator, Ramesh
Subedi, will keep you apprised of the situation.

We are keeping up-to-date the run plan

Daily Run Plan
https://prex.jlab.org/wiki/index.php/RunPlanDaily

Global Plan:
https://prex.jlab.org/wiki/index.php?title=RunPlan

After fixing the target vacuum we'll want to get
into production, interleaved with a few auxiliary
measurements and studies of the polarimeters.

Sincerely
Robert
-------------------------------------------------------
Robert W. Michaels           http://www.jlab.org/~rom
Staff Scientist              phone (757) 269 7410
Thomas Jefferson National Accelerator Facility
12000 Jefferson Ave, Newport News, VA 23606 USA