Diquarks and Exotic Spectroscopy

We propose that the recently discovered Θ⁺ baryon is a bound state of four quarks and an antiquark, containing two highly correlated $ud$ pairs. If so, the Θ⁺ has positive parity, and it lies in an near-ideally mixed SU(3)f 10̄f8f. The Roper resonance and the P₁₁(1710) fit naturally into this classification. We predict an isospin $3/2$ multiplet of Ξ's (S=-2) with J^Π=1/2⁺ 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 analogs of the Θ⁺ may be stable against strong decays.