Role of the Hoyle state in 12CÂ +Â 12C fusion

The 12C + 12C fusion reaction is investigated in a multichannel folding model, using the density-dependent DDM3Y nucleon-nucleon interaction. The 12C(01+,2+,02+,3−) states are included, and their densities are taken from a microscopic cluster calculation. Absorption to fusion channels is simulated by a short-range imaginary potential, and the model does not contain any fitting parameter. We compute elastic and fusion cross sections simultaneously. The role of 12C + 12C inelastic channels, and in particular of the 12C(01+) + 12C(02+) channel involving the Hoyle state, is important even at low energies. In the Gamow region, the energy range relevant in astrophysics, inelastic channels increase the S factor by a factor of three.