Even parity Θ pentaquark and stable antistrange nuclear matter

The newly discovered exotic Θ baryon of mass 1540 MeV (and very small width) truly has a very low mass, if it is a pentaquark system of even parity. A schematic model in which the coherent interaction of us and ds pairs leads to a very large residual attractive interaction is introduced. This collective vibrational model accounts for the mass and small decay width to the KN channel, but yields a significant coupling to the virtual K*N channel. The schematic model predicts an attractive Θ-nucleon interaction sufficient to produce a Θ-nuclear bound state stable against strong decays. The discovery of Θ-nuclei could be a proof that the Θ parity is even