Schematic model for narrow Δ(1232) resonances bound in a nucleus -: art. no. 064605

A schematic model explaining the recent evidence for bound states of the Delta (1232) resonance in C-12 With a width of about 5 MeV found in the C-12(e,e' p pi (-))C-11(g.s.) is suggested. It interprets the observed narrow resonances as coherent bound states enforcing a fixed phase relation for the rescattering of the decay pi 's in the nucleus. The coherent summing of the rescattering diagrams results in a cancellation of the tails of the resonance and a constructive interference in the maximum of the resonance leading to the observed narrow states at the maximum of the Delta (1232) shifted by the binding energy. The same mechanism may contribute to narrow Sigma hypernuclear states and explains their successful and failed observation, respectively.