Search for the H-dibaryon as a ΛΛ resonance

The discovery of pentaquark baryons has attracted new attention to the search for the sixquark (hexaquark) object. Since the observation of double-Λ hypernuclei, the hypothesized H-dibaryon can no longer exist below the ΛΛ mass by more than a few MeV. Enhanced ΛΛ production near threshold, which has been reconfirmed by two other experiments, was first observed in 12C(K-,K+)ΛΛ X reactions at KEK-PS and reflects the possible existence of a ΛΛ resonance, which is referred to as an H-dibaryon resonance state. The present study of ΛΛ enhancement near threshold has been performed to study the spin of the parent particle decaying into ΛΛ. It should be noted that the ΛΛ resonance(s) below 2.261 GeV/c2 is likely to be a spin 0 state.