First measurement of the low-energy direct capture in 20Ne(p, γ)21Na and improved energy and strength of the Ecm = 368 keV resonance

The ${}^{20}\mathrm{N}\mathrm{e}(\mathrm{p},\gamma {)}^{21}\mathrm{N}\mathrm{a}$ reaction is the slowest in the NeNa cycle and directly affects the abundances of the Ne and Na isotopes in a variety of astrophysical sites. Here we report the measurement of its direct capture contribution, for the first time below $E{}_{\mathrm{c}\mathrm{m}}=352$~keV, and of the contribution from the $E_{cm}^{}=368$~keV resonance, which dominates the reaction rate at $T=0.03-1.00$~GK. The experiment was performed deep underground at the Laboratory for Underground Nuclear Astrophysics, using a high-intensity proton beam and a windowless neon gas target. Prompt $\gamma$ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength $\omega \gamma =(0.112\pm {0.002}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}}\pm {0.005}_{\mathrm{s}\mathrm{y}\mathrm{s}})$~meV, with an uncertainty a factor of $3$ smaller than previous values. Our revised reaction rate is 20% lower than previously adopted at $T<0.1$~GK and agrees with previous estimates at temperatures $T\ge 0.1$~GK. Initial astrophysical implications are presented.