Elimination of $0^{+}$ spurious states in the quasiparticle time blocking approximation

Abstract

The quasiparticle time blocking approximation (QTBA) is considered as a model for the description of excitations in open-shell nuclei. The QTBA is an extension of the quasiparticle random phase approximation that includes quasiparticle-phonon coupling. In the present version of the QTBA, the pairing correlations are included within the framework of the BCS approximation. Thus, in this model, the $0^{+}$ spurious states appear, which are caused by the breaking of the symmetry related to the particle-number conservation. In this work, the method is described which solves the problem of the $0^{+}$ spurious states in the QTBA with the help of the projection technique. The method is illustrated by calculations of $0^{+}$ excitations in ${}^{120}$Sn nucleus.

Comments: 12 pages, 3 figures - To appear in the proceedings of the 59-th International Meeting on Nuclear Spectroscopy and Nuclear Structure, June 15-19, 2009, Cheboksary, Russia