Are ${\Theta }^{+}$ and the Roper resonance diquark-diquark-antiquark states?

Abstract

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.

9 pages RevTex4 and 3 eps figures. Revised version accepted for publication in Phys. Lett. B