Decays of M2 baryonium states and a new scheme of baryonium assignment

Assuming the existence of M2 baryonium states, which have a structure of a large closed string and a quark-antiquark pair, we study their decay properties on the basis of duality and unitarity. It is shown that M2 decays involving tree-type hadrons are strongly suppressed by a mechanism similar to the small breaking of the OZI rule in conventional meson decays, while the decay into two M2's is not suppressed. The total width of an M2 state is then narrow below the lowest two-M2 threshold, say 3 GeV. A new scheme of baryonium assignment is suggested: Below 3 GeV observed narrow states are assigned to M2 states and wide ones to M4 states. (author)