The α-decay of the Hoyle state in 12C: a new high-precision investigation

The αdecay path of the Hoyle state in 12 C (E x = 7:654MeV) represents one ofthe most challenging questions of modern nuclear physics. Its knowledge can help in theunderstanding of cluster configurations in light nuclei and the possible existence of Bose-Einstein condensates in nuclei. In stars, it is involved in the so-called 3αprocess, wherethe 12 C nucleosynthesis occurs. We studied the 14 N(d; α2) 12 C(7:654) reaction at 10:5MeVincident energy to probe its direct decay component. We found, with a precision higherof a factor 5 than any other previous experiment, an almost total absence of direct decaysby-passing the ground state of 8 Be. From our analysis, a new upper limit of such decayis found at 0:043% (95% C.L.). Astrophysical 3α process reaction rate calculations haveto be accordingly revised.