Hypernuclear Studies
Hypernuclear physics is expected to be a major part of the
CEBAF program.
the Lambda-hypernucleus, a nuclear system with strangeness S = -1 in which
a Lambda-hyperon replaces one of the nucleons, is a long-lived baryon
system (lifetime is about 10**(-10) sec) and provides us with a variety
of nuclear phenomena. The hyperon is not excluded by the Pauli principle from
the filled nucleon orbitals and can penetrate deep inside the nucleus.
Weak interactions in the nuclear medium (mesonic Lambda -> N + pi versus
nonmesonic Lambda + N -> N + N decay modes of the hypernucleus) can be
studied as well as possible modification of baryon properties (e.g., the
magnetic moment of the Lambda) in the nuclear enviornment. From low energy
Lambda-p scattering studies information has been obtained on the s-state
Lambda-N interaction but the non-central part of the Lambda-N forces is not
well established. The better systematics of hypernuclear spectroscopy
will yield more precise information on the Lambda-N interaction. Especially
useful information on the spin dependence of the effective Lambda-N interaction
can be obtained from the energy splitting of hypernuclear spin doublets.
High resolution studies of hypernuclear systems have been persued at several
laboratories for many years to obtain information on the spin dependence
of the effective Lambda-N interaction. At the moment only electromagnetic
production of hypernuclei via electron beams of
CEBAF quality
together with the Hall A
high resolution
spectrometers
offers the possibility of high resolution data (280 KeV). This is approximately
an order of magnitude better than resolutions presently available elsewhere.
An experiment to study 1p-shell hypernuclear spectroscopy with high resolution
in Hall A is
conditionally approved for 24 days of beam, contingent upon completion of a
pair of septum magnets which will allow the
Hall A spectrometers
to reach the required forward scattering angles. The majority of the funding
for these devices is to be provided by institutions external to the US.
Although these septa are being built for a specific experiment, they will be
part of the general equipment in the hall.