Probing the nature of the conjectured low-spin wobbling bands in atomic nuclei

TL;DR

This paper investigates low-spin wobbling bands in atomic nuclei, revealing that some are caused by single-particle excitations rather than true wobbling motion, and emphasizes the need for improved experimental methods.

Contribution

It demonstrates that certain low-spin wobbling bands are due to single-particle excitations, challenging previous interpretations and proposing new experimental approaches.

Findings

One wobbling band in $^{187}$Au is generated by single-particle excitation.

Previous research paradigms may lead to unreliable identification of wobbling bands.

New experimental methods are needed to distinguish excitation mechanisms.

Abstract

Precession is a unique motion in which the orientation of the rotational axis of a rotating body is not fixed but moving, and it generally exists in the Universe from giant stars through tiny atomic nuclei. In principle, the precession of an atomic nuclide can be approximately described as wobbling motion, arising from the coupling of a rotation and a harmonic vibration. Recently, a number of wobbling bands were reported at low spin, which violate the wobbling approximation that can be valid only at high spin. Here we explore the nature of the reported low-spin wobbling bands. Via a new experiment, we demonstrate that one such band in $^{187}$Au is generated by dominant single-particle excitation rather than by the excitation of a wobbling phonon. We point out that the imperfect research paradigm used previously would lead to unreliable identification of low-spin wobbling bands. Consequently, new experimental approaches should be developed to distinguish among the different excitation mechanisms that can give rise to the observed low-spin bands in odd-even nuclei.