First Observation of Solar Neutrino Interactions on ¹³C

The SNO+ Collaboration reports the first evidence of ⁸B solar neutrinos interacting on ¹³C nuclei. The charged current interaction proceeds through ¹³C + νₑ → ¹³N + e⁻ which is followed, with a 10 minute half-life, by ¹³N → ¹³C + e⁺ +νₑ . 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$σ$. Using the natural abundance of ¹³C present in the scintillator, 5.7 tonnes of ¹³C over 231 days of data were used in this analysis. The 5.6+3.0-2.3 detected events in the data set are consistent with the expectation of 4.7+0.6-1.3 events. This result is the second real-time measurement of CC interactions of ⁸B neutrinos with nuclei and constitutes the lowest energy observation of neutrino interactions on ¹³C generally. This enables the first direct measurement of the CC νₑ reaction to the ground state of ¹³N, yielding an average cross section of (16.1 +8.5-6.7 (stat.) +1.6-2.7 (syst.) )× 10⁻⁴³ cm² over the relevant ⁸B solar neutrino energies.