Quark Model Perspectives on Pentaquark Exotics

A large number of experiments now appear to confirm the existence of the exotic, strangeness +1 θ baryon. The I = 3/2 exotic Ξ3/2 signal observed by NA49 remains to be confirmed (it is not seen by HERA-B, and its compatibility with earlier high statistics Ξ production experiments has also been questioned). Recently, H1 reported evidence for an anti-charmed exotic, though this state was not seen by ZEUS. Whether or not the NA49 and H1 signals are confirmed by subsequent experiments, the existence of the θ makes a rethinking of our understanding of the excited baryon spectrum inevitable. If the θ has I = 0, and lies in a 10F multiplet, for example, exotic pentaquark partners having N and Σ quantum numbers necessarily also exist. These should sit in the same region as the 3q radial excitations of the N and Σ ground states and, unavoidably, mix with them. This immediately calls into question past quark model