Improved Limit on Direct α Decay of the Hoyle State

May 2012 • 2012PhRvL.108t2501K

Authors • Kirsebom, O. S. • Alcorta, M. • Borge, M. J. G. • Cubero, M. • Diget, C. Aa. • Fraile, L. M. • Fulton, B. R. • Fynbo, H. O. U. • Galaviz, D. • Jonson, B. • Madurga, M. • Nilsson, T. • Nyman, G. • Riisager, K. • Tengblad, O. • Turrión, M.

Abstract • The current evaluation of the triple-α reaction rate assumes that the α decay of the 7.65 MeV, 0⁺ state in C12, commonly known as the Hoyle state, proceeds sequentially via the ground state of Be8. This assumption is challenged by the recent identification of two direct α-decay branches with a combined branching ratio of 17(5)%. If correct, this would imply a corresponding reduction in the triple-α reaction rate with important astrophysical consequences. We have used the B11(He3,d) reaction to populate the Hoyle state and measured the decay to three α particles in complete kinematics. We find no evidence for direct α-decay branches, and hence our data do not support a revision of the triple-α reaction rate. We obtain an upper limit of 5×10^-3 on the direct α decay of the Hoyle state at 95% C.L., which is 1 order of magnitude better than a previous upper limit.

Links

• ELECTR http://link.aps.org/doi/10.1103/PhysRevLett.108.202501