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

The SNO+ Collaboration reports the first evidence of ^{8}B solar neutrinos interacting on ^{13}C nuclei. The charged current interaction proceeds through ^{13}C+ν_{e}→^{13}N+e^{-} which is followed, with a 10 minute half life, by ^{13}N→^{13}C+e^{+}+ν_{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 4.2σ. Using the natural abundance of ^{13}C present in the scintillator, 5.7 metric tons of ^{13}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}B neutrinos with nuclei and constitutes the lowest energy observation of neutrino interactions on ^{13}C generally. This enables the first direct measurement of the CC ν_{e} reaction to the ground state of ^{13}N, yielding an average cross section of (16.1_{-6.7}^{+8.5}(stat.)_{-2.7}^{+1.6}(syst.))×10^{-43} cm^{2} over the relevant ^{8}B solar neutrino energies.