On the spin, parity and nature of the $\Xi (1620)$ resonance

Abstract

Using a unitary extension of chiral perturbation theory with a lowest-order s-wave SU(3) chiral Lagrangian we study low-energy meson-baryon scattering in the strangeness $S=-2$ sector. A scattering-matrix pole is found around 1606 MeV which corresponds to an s-wave $\Xi$ resonance with $J^P=1/2^{-}$. We identify this resonance with the $\Xi (1620)$ state, quoted in the Particle Data Book with $I=1/2$ but with unknown spin and parity. The addition of the $S=-2$ state to the recently computed $\Lambda (1670)$, $\Sigma (1620)$ and N(1535) states completes the octet of $J^P=1/2^{-}$ resonances dynamically generated in this chiral unitary approach.

Comments: 8 pages, 1 figure