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

TL;DR

This paper presents a projection technique to eliminate spurious $0^+$ states caused by particle-number symmetry breaking in the QTBA model, improving the accuracy of nuclear excitation descriptions.

Contribution

The paper introduces a novel projection method to remove $0^+$ spurious states in QTBA, enhancing the model's reliability for open-shell nuclei.

Findings

Successful elimination of $0^+$ spurious states in $^{120}$Sn

Improved description of nuclear excitations in QTBA

Method applicable to other open-shell nuclei

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.