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

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The ²⁰Ne(p, γ)²¹Na 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 Ecm = 352~keV, and of the contribution from the Ecm = 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 $γ$ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength ωγ~=~(0.112 ± 0.002ₛₜₐₜ~±~0.005sys)~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 ≥ 0.1~GK. Initial astrophysical implications are presented.