Improved Direct Measurement of the 64.5 keV Resonance Strength in the ^17O(p,α)^14N Reaction at LUNA

The ^17O(p,α)^14N reaction plays a key role in various astrophysical scenarios, from asymptotic giant branch stars to classical novae. It affects the synthesis of rare isotopes such as ^17O and ^18F, which can provide constraints on astrophysical models. A new direct determination of the E_R=64.5  keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator has led to the most accurate value to date ωγ=10.0±1.4_stat±0.7_syst  neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at E_x=5672  keV in ^18F is Γ_p=35±5_stat±3_syst  neV. This width is about a factor of 2 higher than previously estimated, thus leading to a factor of 2 increase in the ^17O(p, α)^14N reaction rate at astrophysical temperatures relevant to shell hydrogen burning in red giant and asymptotic giant branch stars. The new rate implies lower ^17O/^16O ratios, with important implications on the interpretation of astrophysical observables from these stars.