Direct measurement of resonances in ${}^7$Be($\alpha ,\gamma$)${}^{11}$C relevant to $\nu p$-process nucleosynthesis

We have performed the first direct measurement of two resonances of the ${}^7$Be($\alpha ,\gamma$)${}^{11}$C reaction with unknown strengths using an intense radioactive ${}^7$Be beam and the DRAGON recoil separator. We report on the first measurement of the 1155 and 1110 keV resonance strengths of $1.73\pm 0.25(stat\mathrm{.})\pm 0.40(syst\mathrm{.})$ eV and $125_{-25}^{+27}(stat\mathrm{.})\pm 15(syst\mathrm{.})$ meV, respectively. The present results have reduced the uncertainty in the ${}^7$Be($\alpha ,\gamma$)${}^{11}$C reaction rate to $\sim$ 9.4-10.7% over T = 1.5-3 GK, which is relevant for nucleosynthesis in the neutrino-driven outflows of core-collapse supernovae ($\nu p$-process). We find no effect of the new, constrained reaction rate on $\nu p$-process nucleosynthesis.