Nucleon-pair shell model calculations of the even-even Xe and Ba nuclei

The nucleon-pair shell model, truncated to an SD subspace, is applied to 128-134Xe and 130-136Ba. The spectra, eigenstates, and electromagnetic transition strengths of these nuclei, which are known to display O(6) symmetry, are described in terms of a three-parameter Hamiltonian. Agreement with experiment is good, in particular, mixed-symmetry configurations and the upward shift and fragmentation of the M1 strength with increasing neutron numbers emerges naturally. The results show that the SD subspace approximation improves with the number of pairs