Nuclear pairing and pairing vibrations in stable and neutron-rich nuclei

Studies on pairing effects in both nuclear matter and finite nuclei have known intensified interest in the recent years. However, constructing and constraining the pairing interaction is a difficult task and several directions for extensions and improvements may be explored. Some of these improvements can be for instance: i) choosing a richer structure of the pairing interaction by explicitly introducing an isospin dependence, ii) using also the features of nuclear matter for fitting the parameters of pairing interaction to be used for nuclei, iii) considering additional observables than the usual odd-even mass staggering in nuclei to constrain the interaction. Investigations around points i) and ii) have been started and are performed more and more extensively. We concentrate here on the analysis of point iii) and suggest pairing vibrations as additional observables that can be measured through two-particle transfer in nuclei. These observables may eventually allow to explore isospin-asymmetry dependence in the pairing channel if isotopic chains are systematically analyzed. In the framework of self-consistent mean field with Skyrme interactions in the particle-hole channel and a zero-range density-dependent interaction in the pairing channel, we study the response associated to two-neutron transfer in Sn isotopes. We show that the spectrum of the associated excitation modes, the pairing vibrations, is sensitive, especially in neutron-rich nuclei, to the features of the used pairing interaction, namely to its surface/volume character.(author)