Studies of exotic baryon structure in the light quark sector with the BGOOD photoproduction experiment

The discoveries of the pentaquark states and XYZ mesons in the charmed quark sector initiated a new epoch in hadron physics, where the existence of exotic multi-quark states beyond the conventional valence three quark and quark-antiquark systems has been confirmed. Such states could manifest as single colour bound objects, or evolve from meson-baryon and meson-meson interactions, creating molecular like systems and re-scattering effects near production thresholds. Equivalent structures may be evidenced in the light, uds sector, which is the focus of research at the BGOOD photoproduction experiment at the ELSA accelerator in Bonn, Germany. Our results in the strangeness sector suggest a dominant role of meson-baryon dynamics which has an equivalence to the P C states in the charmed sector. This includes structure in K 0 Σ 0 and K + ( Λ ( 1405 ) → π 0 Σ 0 ) photoproduction at the K * Y threshold and a peak at the K + K − p threshold in K + Σ − photoproduction which is only evident at very low momentum transfer kinematics. In the non-strange sector, our measurements of the coherent reactions, γd → π 0 π 0 d, γd → π 0 ηd and γd → π 0 π 0 π 0 d exhibit forward differential cross sections an order of magnitude higher than phenomenological model calculations. This is consistent with intermediate dibaryon formation, including the proposed d *(2380) hexaquark, however other mechanisms, such as final state interactions may yet prove to play dominant roles.