Direct observation of the decay of first excited Hoyle state in $^{12}$C

TL;DR

This study directly observed the decay of the first excited Hoyle state in carbon-12 through exclusive inelastic scattering, providing new insights into its energy, width, and decay pathways.

Contribution

First direct observation of the decay of the first excited Hoyle state in $^{12}$C using event-by-event kinematic reconstruction.

Findings

Identified an excited state at E$_x$ ~ 9.65 MeV in $^{12}$C.

Measured the state's width as approximately 607 keV.

Suggested the state as a candidate for the 2$_2^+$ first excited Hoyle state.

Abstract

An excited state of $^{12}$C having excitation energy E$_x \sim$ 9.65 $\pm$ 0.02 MeV and width (FWHM) $\sim607\pm$ 55 keV, which decays to three $ \alpha $-particles via Hoyle state ($E_x \sim$ 7.65 MeV), has been directly identified for the first time in the exclusive inelastic scattering of 60 MeV $^{4}$He on $^{12}$C, measured in coincidence with the recoiling $^{12}$C$ ^* $ Hoyle state (decaying mostly as $^{12}$C$ ^* $ $\rightarrow \ ^{8} $Be + $ \alpha $ $\rightarrow \ \alpha + \alpha + \alpha$) by event-by-event kinematic reconstruction of the completely detected (4$ \alpha $) events. This state is likely to be a candidate for 2$_2^+$ first excited Hoyle state, the existence of which has recently been indirectly evidenced from the recent inclusive inelastic scattering studies.