New astrophysical S factor for the 15N(p,γ)16O reaction via the asymptotic normalization coefficient (ANC) method

The N-15(p,gamma)O-16 reaction provides a path from the CN cycle to the CNO bi-cycle and CNO tri-cycle. The measured astrophysical factor for this reaction is dominated by resonant capture through two strong J(pi) = 1(-) resonances at E-R = 312 and 962 keV and direct capture to the ground state. Asymptotic normalization coefficients (ANCs) for the ground and seven excited states in O-16 were extracted from the comparison of experimental differential cross sections for the N-15(He-3,d)O-16 reaction with distorted-wave Born approximation calculations. Using these ANCs and proton and alpha resonance widths determined from an R-matrix fit to the data from the N-15(p,alpha)C-12 reaction, we carried out an R-matrix calculation to obtain the astrophysical factor for the N-15(p,gamma)O-16 reaction. The results indicate that the direct capture contribution was previously overestimated. We find the astrophysical factor to be S(0) = 36.0 +/- 6.0 keV b, which is about a factor of 2 lower than the presently accepted value. We conclude that for every 2200 +/- 300 cycles of the main CN cycle one CN catalyst is lost due to this reaction.