Almost medium-free measurement of the Hoyle state direct-decay component with a TPC

International audienceBackground: The structure of the Hoyle state, a highly α-clustered state at 7.65 MeV in C12, has long been the subject of debate. Understanding if the system comprises of three weakly interacting α particles in the 0s orbital, known as an α-condensate state, is possible by studying the decay branches of the Hoyle state. Purpose: The direct decay of the Hoyle state into three α particles, rather than through the Be8 ground state, can be identified by studying the energy partition of the three α particles arising from the decay. This paper provides details on the breakup mechanism of the Hoyle stating using a new experimental technique. Method: By using β-delayed charged-particle spectroscopy of N12 using the Texas active target time-projection chamber, a high-sensitivity measurement of the direct 3α decay ratio can be performed without contributions from pileup events. Results: A Bayesian approach to understanding the contribution of the direct components via a likelihood function shows that the direct component is