Radiative annihilation ofK−p atoms and theΛ(1405)

The radiative annihilations of $K^{\mathrm{-}}$p atoms to Λγ and ${\Sigma }^0$γ are shown to be dominated by the Λ(1405) hyperon. These processes thus provide a sensitive probe of the properties of this controversial state. We show that present data on the Λγ branching ratio are in agreement with its interpretation as a normal quark-model state, and that further information on the Λγ and the comparably strong ${\Sigma }^0$γ channel will provide compelling tests of the viability of this versus the K¯N bound-state interpretation.