Using sub-Coulomb alpha transfer reactions to study the low-energy C-12(alpha,gamma)O-16 S-factor

The C-12(alpha, gamma)O-16 reaction is crucial for the understanding of He burning in massive stars, but the low-energy cross section is highly uncert ain. We have thus explored a new method for studying this process, the sub- Coulomb a transfer reactions C-12(Li-6,d)O-16 and C-12(Li-7,t)O-16 leading to the bound 2(+) and 1(-) states of O-16. At sub-Coulomb energies the reac tion data can be analyzed to obtain the reduced a widths of these states. T ogether with capture and phase-shift data, these results provide for a more accurate determination of the low-energy C-12(alpha, gamma)O-16 S-factor: S-E1(0.3 MeV) = 101 +/- 17 keV b and S-E2(0.3 MeV) = 42(-23)(+16) keV b for the E1 and E2 multipole components of the reaction.