A new high-precision upper limit of direct α-decays from the Hoyle state in 12C

The Hoyle state in 12 C( E x = 7.654MeV) is characterized by a pronounced 3 α cluster configuration. It is involved in the so-called 3 α process in stars, that is responsible of 12 C nucleosynthesis. We studied the decay path of the Hoyle state by using the 14 N(d, α 2 ) 12 C(7.654) reaction at 10.5MeV incident energy. We found, with a precision higher of a factor 5 than any other previous experiment, an almost total absence of direct decays by-passing the ground state of 8 Be. A new upper limit of such a decay width is placed at 0.043% (95% C.L.). Astrophysical 3 α process reaction rate calculations have to be consequently revised.