No abstract

We report a measurement of a new high spin J π = 5 − state at 22.4(0.2) MeV in 12 C 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 12 C 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 12 C 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 12 C.

We propose a description of cluster states in nuclei in terms of representations of unitary algebras U (ν + 1), where ν is the number of space degrees of freedom. Within this framework, a variety of situations including both vibrational and rotational spectra, soft and rigid configurations, identical and non-identical constituents can be described. As an example, we show how the method can be used to study α clustering configurations in 12 C with point group symmetry D 3h .

The algebraic treatment of baryons is extended to strange resonances. Within this framework we study a collective string-like model in which the radial excitations are interpreted as rotations and vibrations of the strings. We derive a mass formula and closed expressions for strong and electromagnetic decay widths and use these to analyze the available experimental data.