Excited Heavy Baryons and Their Symmetries III: Phenomenology

Abstract

Phenomenological applications of an effective theory of low-lying excited states of charm and bottom isoscalar baryons are discussed at leading and next-to-leading order in the combined heavy quark and large $N_c$ expansion. The combined expansion is formulated in terms of the counting parameter $λ\sim 1/m_Q, 1/N_c$; the combined expansion is in powers of $λ^{1/2}$. We work up to next-to-leading order. We obtain model-independent predictions for the excitation energies, the semileptonic form factors and electromagnetic decay rates. The spin-averaged mass of the doublet of the first orbitally excited sate of $Λ_b$ is predicted to be approximately $5920 MeV$. It is shown that in the combined limit at leading and next-to-leading order there is only one independent form factor describing $Λ_b \to Λ_c \ell \barν$; similarly, $Λ_b \to Λ_{c}^{*} \ell \barν$ and $Λ_b \to Λ_{c1} \ell \barν$ decays are described by a single independent form factor. These form factors are calculated at leading and next-to-leading order in the combined expansion. The electromagnetic decay rates of the first excited states of $Λ_c$ and $Λ_b$ are determined at leading and next-to leading order. The ratio of radiative decay rates $Γ(Λ_{c}^{*} \to Λ_c γ) / Γ(Λ_{b1} \to Λ_b γ)$ is predicted to be approximately 0.2, greatly different from the heavy quark effective theory value of unity.

21 pages, 2 figures