The Hypernuclear Spectroscopy Program at Jefferson Lab

The central question of nuclear science is the structure of nuclear matter. For a complete

understanding of the evolution of nuclear matter in the universe, detailed

knowledge is necessary not only for stable nuclei, but also increasingly for

unstable and exotic nuclear matter. Nuclear matter containing strangeness is

thought to play an important role in stellar objects like neutron stars. The

knowledge of the underlying interaction between strange baryons (hyperons) and

nucleons (protons and neutrons) is incomplete. A complete theory of

baryon-baryon interactions in the context of the underlying QCD degrees of

freedom, quarks and gluons, will ultimately also have to describe interactions

with and between strange baryons. In the laboratory, these can be best studied

by implanting hyperons in ordinary nuclei, thus converting them to hypernuclei.

The high quality electron beam at Jefferson Lab allowed for the first time to

study hypernuclei by (e,e'K$^+$) reaction spectroscopy. Six experiments on

a number of light to medium heavy targets were conducted.

Currently, the hypernuclear spectroscopy system at Jefferson Lab is being

upgraded to ensure compatibility with the higher beam energies after the 12 GeV

upgrade. Four new experiments have already been approved.

They will measure the hyperhydrogen nuclei which will addresses charge symmetry

breaking or isospin dependence. Spectroscopy 40K and

48K hypernucllei will study the isospin dependence of the 3-body Lambda-nn

force. Finally, a study on a lead target will provide data on an extended nucleus with large neutron excess;

this is the closest approximation to neutron star matter than can be achieved

in the laboratory.

In this talk, I will review the results from the previous program and conclude with an outlook

on the future experiments.