Evidence for Triangular D_3h Symmetry in 12C

TL;DR

This paper provides evidence for D_3h symmetry in the nucleus 12C by identifying a high-spin state consistent with a triangular rotational band, marking the first such observation in nuclear physics.

Contribution

It reports the first experimental evidence of D_3h symmetry in a nucleus, linking nuclear structure to molecular symmetry concepts and proposing further measurements to explore clustering in 12C.

Findings

Identification of a high-spin 5- state at 22.4 MeV in 12C

Observation of a rotational band consistent with D_3h symmetry

Suggestion of new measurements to find missing states in the Hoyle band

Abstract

We report a measurement of a new high spin Jp = 5- state at 22.4(0.2) MeV in 12C which fits very well to the predicted (ground state) rotational band of an oblate equilateral triangular spinning top with a D_3h symmetry characterized by the sequence 0+, 2+, 3-, 4+/-, 5- with almost degenerate 4+ and 4- (parity doublet) states. Such a D_3h symmetry was observed in triatomic molecules and it is observed here for the first time in nuclear physics. We discuss a classification of other rotation-vibration bands in 12C such as the (0+) Hoyle band and the (1-) bending mode band and suggest measurements in search of the predicted ("missing") states that may shed new light on clustering in 12C and light nuclei. In particular the observation (or non-observation) of the predicted ("missing") states in the Hoyle band will allow us to conclude the geometrical arrangement of the three alpha-particle composing the Hoyle state at 7.654 MeV in 12C.