Charm and bottom baryon masses in the 1/N expansion

The 1/Nc expansion has proven useful for studying the spin-flavor properties of baryons containing light quarks. A spin-flavor symmetry for baryons is defined in large-Nc QCD. Away from the Nc → ∞ limit, 1/Nc corrections which break large-Nc baryon spin-flavor symmetry can be classified in terms of the spin and flavor symmetries which remain for finite Nc. Since explicit SU(3) flavor symmetry breaking ǫ ∼ ms/Λχ is comparable to 1/Nc = 1/3 for QCD baryons, a combined expansion in 1/Nc and ǫ is necessary to explain the symmetry-breaking pattern. The 1/Nc expansion has had considerable phenomenological success for qqq baryons; 1/Nc suppression factors clearly are present in experimental data. For baryons containing a single heavy quark Q in HQET, there is spin-flavor symmetry in the large-Nc limit as well as in the heavy quark limit [1]. The spin-flavor symmetry of heavy quark baryons with one heavy quark flavor contains a SU(6)l symmetry of the light degrees of freedom in the Nc → ∞ limit, and a SU(2)Q spin symmetry of the heavy quark in both the mQ → ∞ and Nc → ∞ limits. The spinflavor symmetry of the light degrees of freedom is broken by corrections suppressed by factors of 1/Nc and SU(3) flavor symmetry breaking, whereas the heavy-quark spin symmetry is broken by terms suppressed by factors of 1/Nc and heavy quark symmetry breaking δQ ∼ ΛQCD/mQ. Note