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WASA finds evidence for a six-quark state

Experiments performed by the WASA-at-COSY collaboration have now found compelling evidence for a new state in the two-baryon system, with mass 2380 MeV and width 70 MeV. The structure, containing six valence quarks, constitutes a so-called dibaryon, either an exotic compact particle or a hadronic molecule.

Polarized proton-neutron scatteringEnergy dependence of the analyzing power near 90 degrees, where the maximum of the resonance effect occurs. Red symbols exhibit the new measurements. Dashed and solid lines show the SAID partial-wave solution with and without resonance.
Copyright: WASA-at-COSY Collaboration

The result answers the long-standing question of whether there are more eigenstates in the two-baryon system than just the deuteron ground-state. This fundamental question has been awaiting an answer at least since 1964, when first Freeman Dyson and later-on Robert Jaffe envisaged the possible existence of non-trivial six-quark configurations. The new structure has been observed in high-precision measurements carried out by the WASA-at-COSY collaboration. First signals of this new state had been seen before in neutron-proton collisions, where a deuteron is produced together with a pair of neutral pions. Now this state has also been observed in polarized neutron-proton scattering itself and extracted by application of the partial-wave analysis technique - the generally accepted ultimate method to reveal a resonance.