Odd parity bottom-flavored baryon resonances

Abstract

The LHCb Collaboration has recently observed two narrow baryon resonances with beauty. Their masses and decay modes look consistent with the quark model orbitally excited states ${\ensuremath{\Lambda}}_{b}(5912)$ and ${\ensuremath{\Lambda}}_{b}^{*}(5920)$, with quantum numbers ${J}^{P}=1/{2}^{\ensuremath{-}}$ and $3/{2}^{\ensuremath{-}}$, respectively. We predict the existence of these states within a unitarized meson-baryon coupled-channel dynamical model, which implements heavy-quark spin symmetry. Masses, quantum numbers and couplings of these resonances to the different meson-baryon channels are obtained. We find that the resonances ${\ensuremath{\Lambda}}_{b}^{0}(5912)$ and ${\ensuremath{\Lambda}}_{b}^{0}(5920)$ are heavy-quark spin symmetry partners, which naturally explains their approximate mass degeneracy. Corresponding bottom-strange baryon resonances are predicted at ${\ensuremath{\Xi}}_{b}(6035.4)$ (${J}^{P}=\frac{1}{2}\genfrac{}{}{0}{}{{}^{\ensuremath{-}}}{}$) and ${\ensuremath{\Xi}}_{b}(6043.3)$ (${J}^{P}=\frac{3}{2}\genfrac{}{}{0}{}{{}^{\ensuremath{-}}}{}$). The two ${\ensuremath{\Lambda}}_{b}$ and two ${\ensuremath{\Xi}}_{b}$ resonances complete a multiplet of the combined symmetry SU(3)-flavor times heavy-quark spin.