The hybrid configuration mixing model and the spectroscopy of odd nuclei

We introduce a new approach which is meant to be a step towards complete low-lying spectroscopy of odd nuclei. In the first applications, we limit ourselves to a magic core plus an extra neutron or proton. The model does not contain any free adjustable parameter, but is based on a Hartree-Fock (HF) description of particle states and Random Phase Approximation (RPA) calculations for core excitations. With respect to traditional particle-vibration coupling calculations, in which one can only address single-nucleon states and particle-vibration multiplets, we can also describe states of shell-model type like 2 particle-1 hole. The underlying spirit is, of course, related to filling the gap between shell-model-like approaches for low-lying spectroscopy, and the traditional HF+RPA approach to high-lying states like giant resonances.