We consider a $[ud]^2\bar{ s}$ current in the QCD sum rule framework to study the mass of the recently observed pentaquark state $\Theta^+(1540)$, obtaining good agreement with the experimental value. We also study the mass of the pentaquark $[ud]^2\bar{ d}$. Our results are compatible with the interpretation of the $[ud]^2\bar{ d}$ state as being the Roper resonance N(1440), as suggested by Jaffe and Wilczek.
Categories: hep-ph nucl-th