Longitudinal Wobbling in $^{133}$La

TL;DR

This paper reports the first observation of longitudinal wobbling in a nucleus, specifically in $^{133}$La, supported by experimental data and quasiparticle-triaxial-rotor model calculations, contrasting with previously observed transverse wobbling.

Contribution

It provides the first experimental evidence of longitudinal wobbling in nuclei and explains it using the QTR model, highlighting a new wobbling mode in nuclear physics.

Findings

Identification of wobbling bands with $n__ ho$=0 and 1

Observation of increasing wobbling frequency with spin

First evidence of longitudinal wobbling in nuclei

Abstract

Excited states of $^{133}$La have been investigated to search for the wobbling excitation mode in the low-spin regime. Wobbling bands with $n_\omega$ = 0 and 1 are identified along with the interconnecting $\Delta I$ = 1, $E2$ transitions, which are regarded as one of the characteristic features of the wobbling motion. An increase in wobbling frequency with spin implies longitudinal wobbling for $^{133}$La, in contrast with the case of transverse wobbling observed in $^{135}$Pr. This is the first observation of a longitudinal wobbling band in nuclei. The experimental observations are accounted for by calculations using the quasiparticle-triaxial-rotor (QTR) model, which attribute the appearance of longitudinal wobbling to the early alignment of a $\pi=+$ proton pair.