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.