Determination of the astrophysical S factor for ¹¹C(p,γ)¹²N from the ¹²N⃗¹¹C+p asymptotic normalization coefficient

The evolution of very low-metallicity, massive stars depends critically on the amount of CNO nuclei that they produce. Alternative paths from the slow 3α process to produce CNO seed nuclei could change their fate. The ¹¹C(p,γ)¹²N reaction is an important branch point in one such alternative path. At energies appropriate to stellar evolution of very low-metallicity, massive stars, nonresonant capture dominates the reaction rate. We have determined the astrophysical S factor for the ¹¹C(p,γ)¹²N reaction using the asymptotic normalization coefficient for ¹²N⃗¹¹C+p to fix the nonresonant capture rate. In our experiment, a 110 MeV ¹¹C radioactive beam was used to study the¹⁴N(¹¹C,¹²N)¹³C peripheral transfer reaction and the asymptotic normalization coefficient, (C_peff^12N)²=(C_p1/2^12N)²+(C_p3/2^12N)²=1.73±0.25fm^-1, was extracted from the measured cross section. The contributions from the second resonance and interference effects were estimated using an R-matrix approach with the measured asymptotic normalization coefficient and the latest value for Γ_γ. We find the S factor for ¹¹C(p,γ)¹²N is significantly larger than previous estimates. As a result, the required density for it to contribute is reduced, and more CNO material may be produced.