Pentaquark update after ten years

Abstract

Studying scattering of heavy flavor hadrons and looking for bound states is shown to give experimental information otherwise unobtainable about effective two-body interactions between constituent ( qq) 6 and ( qq) 8 pairs respectively in color sextet and color octet states. All the successes of the constituent quark model in ( uds) hadron spectroscopy are shown to depend only on effective two-body interactions in color 3 ∗ and singlet states. New directions for bound pentaquark searches are discussed following the availability of vertex detectors which can pinpoint events where a proton is emitted from a secondary vertex. Any such event indicates a particle decaying weakly by proton emission and the discovery of a new particle if its mass is higher than that of known charmed baryons. There is no combinatorial background and striking decay signatures like pθπ − are no longer needed. The beauty pentaquark ( bsuud ) and the doubly strange pentaquark ( cssud ) may be relevant to future searches. A simple calculation shows that the effects of flavor-SU(3) breaking on their binding relative to the relevant thresholds are similar to that for the singly strange pentaquark ( csuud ) relative to the D s p threshold.