MULTIPLY STRANGE NUCLEAR SYSTEMS

We investigate the stability of multiply strange baryonic systems, in the context of a mean field approach obtained from an underlying set of phenomenological meson-baryon interactions. The coupling parameters which determine the conventional sigma + omega mean fields (Hartree potentials) seen by various baryon species (N, LAMBDA, XI) in the many-body system are constrained by reproducing the trend of observed binding energies of single particle (N, LAMBDA, XI) states, as well as the energy per particle and density of non-strange nuclear matter. We also consider additional scalar (sigma*) and vector (phi) fields which couple strongly to strange baryons. The couplings of these fields are adjusted to produce strong hyperon-hyperon interactions, as suggested by the data on LAMBDA LAMBDA hypernuclei. Extrapolating this approach to systems of large strangeness S, we find a broad class of objects composed of neutrons, protons, LAMBDA's and XI's, which are stable against strong decay. In these systems, the presence of filled LAMBDA orbitals blocks the strong decay XI N --> LAMBDA LAMBDA, leading to a strangeness fraction f(s) = \S\/A almost-equal-to 1, density rho almost-equal-to (2 - 3) rho0, and charge fraction f(q) in the range - 0.1 < q/A < 0.1, comparable to that of hypothetical stable strange quark matter (''strangelets''), but with a low binding energy per particle E(B)/A almost-equal-to -10 to -20 MeV. We compare with an approximate mass formula which qualitatively describes the results of the mean field calculations. Such weakly bound multi-strange objects can be stable for very large A, unlike ordinary nuclei, since the Coulomb repulsion generated by the protons is largely cancelled by the presence of a comparable number of XI-'s, leading to a small net charge (positive or negative) of order A1/3. We comment on the weak decays of such subjects and the possibility of their production in relativistic heavy ion collisions. (C) 1994 Academic Press, Inc.