Characterization of the proposed 4-{\alpha} cluster state candidate in 16O

TL;DR

This study investigates a candidate 4-alpha cluster state in oxygen-16 through inelastic alpha scattering experiments, revealing a potential new resonance near 15 MeV that may affect previous state identifications.

Contribution

It provides experimental evidence for the 4-alpha cluster state in 16O and suggests the existence of an unresolved resonance near 15 MeV that could influence prior observations.

Findings

Identification of the 0_6^+ state at 15.097 MeV in 16O.

Evidence for a new resonance around 15 MeV that may not be 0^+.

Implication that previous measurements of the 0_6^+ state may have been contaminated.

Abstract

The $\mathrm{^{16}O}(\alpha, \alpha^{\prime})$ reaction was studied at $\theta_{lab} = 0^\circ$ at an incident energy of $\textrm{E}_{lab}$ = 200 MeV using the K600 magnetic spectrometer at iThemba LABS. Proton and $\alpha$-decay from the natural parity states were observed in a large-acceptance silicon-strip detector array at backward angles. The coincident charged particle measurements were used to characterize the decay channels of the $0_{6}^{+}$ state in $\mathrm{^{16}O}$ located at $E_{x} = 15.097(5)$ MeV. This state is identified by several theoretical cluster calculations to be a good candidate for the 4-$\alpha$ cluster state. The results of this work suggest the presence of a previously unidentified resonance at $E_{x}\approx15$ MeV that does not exhibit a $0^{+}$ character. This unresolved resonance may have contaminated previous observations of the $0_{6}^{+}$ state.