Astrophysical SE2 factor of the 12C(α, γ)16O reaction through the 12C(11B, 7Li)16O transfer reaction

The 12C(α, γ)16O reaction plays a key role in the evolution of stars with masses of M > 0.55 M⊙. At the Gamow peak (Ec.m. = 300 ke V, T9 = 0.2), the cross section of the 12C(α, γ)16O reaction is so small (about 10−17 barn) that the direct measurement in ground laboratory is not feasible with the existing technology. Up to now, the cross sections at lower energies can only be extrapolated from the data at higher energies. However, two subthreshold resonances, locating at Ex = 7.117 MeV and Ex = 6.917 MeV, make this extrapolation more complicated. In this work the 6.917 MeV subthreshold resonance in the 12C(α, γ)16O reaction was investigated via the 12C(11B, 7Li)16O reaction. The experiment was performed using the Q3D magnetic spectrograph at HI-13 tandem accelerator. We measured the angular distribution of the 12C(11B, 7Li)16O transfer reaction leading to the 6.917 MeV state. Based on DWBA analysis, we derived the square of ANC of the 6.917 MeV level in 16O to be (2.45± 0.28) ×1010 fm−1, with which the reduced-α width can be computed. Finally, we calculated the astrophysical SE2 factor of the 6.917 MeV resonance to be 67.6 ± 7.7 ke V b.