Spectroscopy of pentaquark states

We construct a complete classification of qqqq¯q pentaquark states in terms of the spin-flavour SU(6) representations. We find that only some definite SU(3) representations are allowed, that is singlets, octects, decuplets, anti-decuplets, 27-plets and 35-plets. The latter three contain exotic states, which cannot be constructed from three quarks only. This complete classification is general and model independent and is useful both for model builders and experimentalists. The mass spectrum is obtained from a Gürsey-Radicati type mass formula, whose coefficients have been determined previously by a study of qqq-baryons. The ground-state pentaquark, which is identified with the recently observed Θ+(1540) state, is predicted to be an isosinglet anti-decuplet state. Its parity depends on the interplay between the spin-flavour and orbital contributions to the mass operator