Diquarks and Exotic Spectroscopy

Abstract

We propose that the recently discovered Θbaryon is a bound state of four quarks and an antiquark, containing two highly correlated ud-pairs. If so, the Θbaryon has positive parity, and it lies in an near-ideally mixed SU(3)_{f} \mathbf{\bar{10}}_{f} oplus \mathbf{8}_{f}. The Roper resonance and the P_{11}(1710) fit naturally into this classification. We predict an isospin 3/2 multiplet of Ξ's (S=-2) with J^Π=\half^{+} around 1750 MeV. A search for manifestly exotic Ξ^{+} and Ξ^{--} in this mass range could provide a sharp test of our proposal. We predict that charm and bottom analogues of the Θbaryon are stable against strong decays.