title: Further improvement of the upper limit on the direct 3α decay from the Hoyle state in 12C.
abstract: The direct 3α decay branch from the 02+ state at Ex=7.65  MeV in 12C, which is known as the Hoyle state, is considered to affect the triple-α reaction rate strongly and to give crucial information on its structure. We have performed a high-precision measurement of the 3α decay from this state using the 12C(12C,3α)12C reaction at E12C=110  MeV. The branching ratio of the direct 3α decay was under the detection limit in the present experiment. By comparing with Monte Carlo simulations for three decay mechanisms as the sequential decay through the ground state of ^{8}Be, the direct decay with equal energies of three α particles, and the direct decay to the phase space uniformly, we have obtained the upper limit of 0.2% on the direct 3α decay.
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Itoh
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Ando
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Aoki
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Arikawa
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Ezure
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Harada
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Hayamizu
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Inoue
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kato
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kawamura
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Sakemi
authors.affiliation: Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Uchiyama