Odd-odd N=Z nuclei and np pairing

The role of pairing correlations in nuclei is well established. For most nuclei, i.e. those with N > Z, the superfluid state consists of neutron (nn) and/or proton (pp) pairs coupled to angular momentum zero and isospin T = 1. At N = Z, the near degeneracy of the proton and neutron orbitals near the Fermi surface opens up the possibility for a different type of Cooper pair consisting of a neutron and a proton (np). This np pair can be coupled to angular momentum zero and isospin T = 1 (isovector), or, since they are no longer restricted by the Pauli exclusion principle, to T = 0 (isoscalar) and the favored angular momenta are J = 1 or J = J(max) [1]. Charge independence of the nuclear force implies that for N = Z nuclei, T = 1 np pairing should exist on an equal footing with T = 1 nn and pp pairing. However, it is an open question whether strongly correlated T = 0 np pairs also exist. The interest in this subject is reflected in the large number of publications, mainly by our theoretical colleagues, and Ramon Wyss has addressed some of these works at this conference[2].