Charmed Baryon Masses in Chiral Perturbation Theory

The masses of the charmed baryons in the ${\bf 6}$ representation of $SU(3)$ obey an equal spacing rule at lowest order in $SU(3)$ breaking, ${\cal O}(m_s)$. We compute the corrections to this relation at order ${\cal O}(m_s^{3/2})$ arising from meson loops using chiral perturbation theory combined with heavy quark symmetry and find them to be small. We also examine the hyperfine interaction responsible for the splitting between the $J^\pi={3\over 2}^+$ and $J^\pi={1\over 2}^+$ baryons in the \ss\ representation. The results also hold in the b-baryon sector.