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

The ¹⁵N(p,γ)¹⁶O 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^π=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 ¹⁶O were extracted from the comparison of experimental differential cross sections for the ¹⁵N(³He,d)¹⁶O reaction with distorted-wave Born approximation calculations. Using these ANCs and proton and α resonance widths determined from an R-matrix fit to the data from the ¹⁵N(p,α)¹²C reaction, we carried out an R-matrix calculation to obtain the astrophysical factor for the ¹⁵N(p,γ)¹⁶O 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.