Schematic study of perturbative effects on the two-neutrino double beta decay to excited states

Abstract

Matrix elements for the two-neutrino double beta decay of 136Xe to the ground and excited states of 136Ba are calculated using a schematic model. The separable proton-neutron interaction includes, in addition to the particle-hole channel, a particle-particle channel. It is found that this force yields nearly the same results as realistic interactions for leading-order QRPA contributions. Perturbative effects associated with the coupling between quasiparticles and phonons, both of the charge-conserving and charge-non-conserving type, are studied and found to be dominated by the coupling to charge-non-conserving 1+ proton-neutron phonons.