Hadron Dynamics  Nuclear Structure  Many Body Problem

Hypernuclei.

The study of hypernuclear structure provides an original alternative approach to the nuclear many body problem. A striking example is the existence of deeply bound states of $\Lambda$'s in a nucleus. The Pauli exclusion principle does not prevent a $\Lambda$ from occupying a deeply lying shell already filled with nucleons. Hypernuclei also represent a unique laboratory for the study of the weak interaction reaction $\Lambda N\rightarrow NN$, that can occur only in nuclear matter and not in vacuum. Meson-exchange and quark model predictions are quite different for the relative strengths of the weak $\Lambda$-neutron and $\Lambda$-proton interactions, but the present data, do not allow a significant test due to their low statistics and large systematic errors. Hypernuclear initial states and nuclear final states may be used as a filter for selecting the quantum numbers in the reaction usually referred to as non-mesonic decays of hypernuclei. In the next five years the completion of two new major experimental facilities will enlarge the present scenario. The FINUDA experiment at DA$\Phi$NE (Frascati), will exploit the low-energy (16 MeV) K^- from $\phi$ decay, background free and tagged, to produce abundantly $\Lambda$ - hypernuclei by the $(K_{stop}^{-},\pi ^{-})$ reaction on several nuclear targets. The momentum transfer involved in the reaction is such that all the spectrum of allowed hypernuclear states will be populated. The good energy resolution will allow a substantial step forward in spectroscopy. The transparent structure of the detector will allow one an unprecedented step forward in the study of the non-mesonic decay of hypernuclei. An extensive research programme on hypernuclear physics with a remarkable energy resolution is planned at CEBAF (Jefferson Lab) using the $(e,e^{\prime }K^{+})$ reaction. The University of Mainz proposes an energy upgrade of MAMI to 1.5 GeV that will also give access to strangeness production. One hopes to disentangle the doublets of states expected by the weak spin-orbit interaction of the $\Lambda$ and to determine their form factors.