Isospin breaking in the $^{71}$Kr and $^{71}$Br mirror system

TL;DR

This paper investigates isospin symmetry breaking in the mirror nuclei $^{71}$Kr and $^{71}$Br, revealing deviations from expected mirror symmetry through experimental beta decay data and shell model calculations, and reports a new state in $^{70}$Se.

Contribution

It provides experimental and theoretical evidence of isospin symmetry breaking in the $^{71}$Kr-$^{71}$Br system and reports a new state in $^{70}$Se.

Findings

Evidence of isospin symmetry breaking in $^{71}$Kr and $^{71}$Br

Observation of a new 0$^+$ state in $^{70}$Se

Shell model calculations support experimental results

Abstract

Isospin symmetry is a fundamental concept in nuclear physics. Even though isospin symmetry is partially broken, it holds approximately for most nuclear systems, which makes exceptions very interesting from the nuclear structure perspective. In this framework, it is expected that the spins and parities of the ground states of mirror nuclei should be the same, in particular for the simplest systems where a proton is exchanged with a neutron or vice versa. In this work, we present evidence that this assumption is broken in the mirror pair $^{71}$Br and $^{71}$Kr system. Our conclusions are based on a high-statistics $\beta$ decay study of $^{71}$Kr and on state-of-the-art shell model calculations. In our work, we also found evidence of a new state in $^{70}$Se, populated in the $\beta$-delayed proton emission process which can be interpreted as the long sought coexisting 0$^+$ state.