[Jlab-seminars] Seminar Announcement

[Luci Collins]

*Seminar
Thursday, April 15, 2009
11:00AM
CCL102-104

* Christopher Bass, NIST - Gaithersburg MD

"Measuring the Parity-Violating Neutron Spin Rotation in Helium:
          The Neutron Spin Rotation Experiment."

A precision measurement of the parity-violating neutron spin rotation in
helium due to the nucleon-nucleon weak interaction has been performed at the
NIST Center for Neutron Research. The measurement employed a beam of low
energy neutrons passing through a liquid helium target system located
between a neutron polarizer--analyzer pair. The magnitude of the
parity-violating spin rotation was determined from measured count
asymmetries in the analyzer. The expected parity-violating spin rotation of
order 10-6 rad placed severe constraints on the apparatus design. In
particular, isolation of the parity-odd component of the spin rotation from
the much larger Larmour precession required use of a nonmagnetic target
system that allowed movement of the target helium upstream or downstream of
a vertical precession coil, which enabled us to take asymmetry differences
and subtract background rotations. The design and performance of the
apparatus used for this experiment will be described, as well as preliminary
results for the measurement, and possible follow-up experiments with reduced
statistical and systematic errors.

 




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