First Evidence of Solar Neutrino Interactions on ${}^{13}$C

Abstract

The SNO+ Collaboration reports the first evidence of ${}^8\text{B}$ solar neutrinos interacting on ${}^{13}\text{C}$ nuclei. The charged current interaction proceeds through ${}^{13}\text{C}+\hat{I}{½}_e\to {}^{13}\text{N}+e^{-}$ which is followed, with a 10 minute half-life, by ${}^{13}\text{N}\to {}^{13}\text{C}+e^{+}+\hat{I}{½}_e.$ The detection strategy is based on the delayed coincidence between the electron and the positron. Evidence for the charged current signal is presented with a significance of 4.2$\ddot{I}ƒ$. Using the natural abundance of ${}^{13}\text{C}$ present in the scintillator, 5.7 tonnes of ${}^{13}\text{C}$ over 231 days of data were used in this analysis. The 5.6${}_{-2.3}^{+3.0}$ observed events in the data set are consistent with the expectation of 4.7${}_{-1.3}^{+0.6}$ events. This result is the second real-time measurement of CC interactions of ${}^8\text{B}$ neutrinos with nuclei and constitutes the lowest energy observation of neutrino interactions on ${}^{13}\text{C}$ generally. This enables the first direct measurement of the CC $\hat{I}{½}_e$ reaction to the ground state of ${}^{13}\text{N}$, yielding an average cross section of $(16.1_{-6.7}^{+8.5}(\text{stat.}{)}_{-2.7}^{+1.6}(\text{syst.}))\times 10^{-43}$ cm${}^2$ over the relevant ${}^8\text{B}$ solar neutrino energies.