Strong and electromagnetic decays of the baryon decuplet

Abstract

To explore further the role that QCD symmetries play on hadron dynamics, we discuss the radiative decay of the baryon decuplet to the baryon octet and compute the leading non-analytic SU(3) violating corrections induced at the one-loop level. In the limit of exact flavour SU(3) symmetry two of the possible decay modes are forbidden and the rates for these two decays are dominated by loop corrections. There is only one SU(3) conserving contact term at leading order in chiral perturbation theory for the radiative decays. We determine its coefficient from the observed branching ratio for Δ → N γ and from the present upper limit on Ξ ∗0 → Ξ 0γ . We then predict the branching fractions for Σ ∗− → Σ − γ, Σ ∗0 → Λγ, Σ ∗0 → Σ 0γ, Σ ∗+ → Σ + γ, Ξ ∗0γ → Ξ 0γ and Ξ ∗− → Ξ −γ . Some of the decay modes are predicted to have branching fractions near the current experimental upper limit and could possibly be observed in the near future. The leading corrections to the octet-decuplet-meson strong coupling constant, C , are computed at one-loop and the strong decay rates of the Δ, Σ ∗ and Ξ ∗ allow us to determine | C| = 1.2 ± 0.1 and H = −2.2 ± 0.6 , in remarkable agreement with predictions based on spin-flavour symmetry. We calculate the Δ pole graph contribution to the polarisability of the nucleon to order 1 Λ χ 2 in chiral perturbation theory.