  We investigate the role the interweaving of surface vibrations and nucleon
motion has on Cooper pair formation in spherical superfluid nuclei. A
quantitative calculation of the state-dependent pairing gap requires to go
beyond the quasiparticle approximation, treating in detail the breaking of the
single-particle strength and of the associated poles. This is done solving
self-consistently the Dyson equation, including both a bare nucleon-nucleon
interaction (which for simplicity we choose as a monopole-pairing force of
constant matrix elements g) and an induced interaction arizing from the
exchange of vibrations (calculated microscopically in QRPA) between pairs of
nucleons moving in time reversal states. Both the normal and anomalous density
Green functions are included, thus treating self-energy and pairing processes
on equal footing. We apply the formalism to the superfluid nucleus 120Sn.
Adjusting the value of g so as to reproduce, for levels close to the Fermi
level, the empirical odd-even mass difference (Delta approx 1.4 MeV), it is
found that the pairing gap receives about equal contributions from the
monopole-pairing force and from the induced interaction. [More sentences
continue. See the main body.]
