Observation of J/ψp Resonances Consistent with Pentaquark States in Λ_b^0 → J/ψK^-p Decays
The LHCb collaboration at CERN's Large Hadron Collider reported the observation of exotic structures in the J/ψp invariant-mass spectrum of Λ_b^0 baryon decays, interpreted as hidden-charm pentaquark states. Two resonant states, labelled Pc(4380)+ and Pc(4450)+, were identified with high statistical significance. The result provided the first compelling evidence for pentaquarks, baryon-like states composed of five quarks.