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 $(\bar qq)_8$ 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 $p \phi \pi^-$ are no longer needed. The beauty pentaquark ($\bar b suud$) and the doubly-strange pentaquark ($\bar c ssud$) 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 ($\bar c suud$) relative to the $D_s p$ threshold.