We compute the leading contribution to the E2/M1 mixing ratio of the decay $\Delta\rightarrow N\gamma$ in heavy baryon chiral perturbation theory. We find the mixing ratio to be $4\% \ltap |\delta_{ \rm E2/M1}| \ltap 11\%$, much larger than estimates based on the quark model and other hadronic models. We also compute the mixing ratio for the radiative decay of the hyperon resonances. The decays $\Sigma^{ *+}\rightarrow\Sigma^+\gamma$ and $\Xi^{ *-}\rightarrow\Xi^-\gamma$ provide a particularly sensitive probe of deviations from heavy baryon spin-flavour SU(6).
Categories: hep-ph nucl-th