C • Neutrino detector located 2 km underground at SNOLAB, in Canada • Acrylic vessel filled with 780 tonnes of liquid scintillator • Ionising radiation generates scintillation light • The light is recorded by the 9362 PMTs • The muon rate is ~3 per hour Physics goals include the search for neutrinoless double beta decay from tellurium-130 and measurements of the reactor, solar, supernovae and, geo neutrinos CC on Carbon-13 𝑒! Prompt Event Delayed Event • Data-driven background rates • The fiducial volume, ΔR, ΔT and delayed energy window were jointly optimised • The annihilation produces two gammas which are detected • A positron with energy: [1.0 to 2.2] MeV • Imposing a 5 MeV cut removes most background, for example, the Thallium-208 decay (Q = 5 MeV) 𝟖𝑩 𝟖𝑩𝒆+ 𝒗𝒆+ 𝒆# Likelihood Analysis 𝑣! &'𝐶 &'𝑁 𝑣! &'𝐶 𝑒( 𝑒! 𝛾 𝛾 𝑡$ % ≈10 𝑚𝑖𝑛 Using PDFs of the delayed energy (1 to 2.2 MeV), ΔT (0.01 to 60 min), and ΔR (<1 m), the Likelihood ratio can be constructed A predetermined cut that maximise significance gives an expected background number of 0.17 and a signal of 1.79 Two events observed, giving a background fluctuation probability of 1% The successfully validated background model gives confidence in the extrapolation of sensitivity Cuts-Based Analysis • The remaining prompt background is 8B Elastic scattering These cuts give an expected background number of 0.31 and a signal of 1.83 Two events observed • Electron with energy = 𝐸(𝜈!) −2.2 𝑀𝑒𝑉 [2] T. Suzuki, A. B. Balantekin, and T. Kajino, Neutrino capture on 13C Phys. Rev. C 86, 015502, 2012 Analysis is being continued on an expanded data set Backgrounds [1] Borexino Collaboration, M. Agostini et al., Comprehensive measurement of pp-chain solar neutrinos, Nature 562, 2018 Gulliver Milton on behalf of the SNO+ collaboration SNO+ experiment Φ "# = 5.20 $%.' (%.' × 10) 𝑐𝑚$*𝑠$' [1] FV < 5.3 m ΔR < 0.36 m 0.01 < ΔT (min) < 24 1.14 < 𝐸!! (MeV) < 2.2 [3] P. A. Zyla et al, (Particle Data Group), Review of Particle Physics, Prog. Theor, Exp. Phys, 083C01, 2020 Livetime: 170 days (pre-cuts), 150 days (post-cuts) • This is obtained by integrating over the theoretical cross- section [2] and SSM 8B neutrino flux [1], assuming the globally fit neutrino oscillations parameters [3] • The dominant background is from accidental coincidences Predetermined cuts First Indications of CC Solar Neutrino Interactions on Carbon-13 Signal • The fraction of events resulting in fake coincidences allows the random coincidence rate to be determined • The cross-section of the interaction is orders of magnitude larger than the electron ES process [2] • In SNO+ there are expected 22 ev/yr/kT 8B neutrino CC interactions with 13C • Given the low muon flux at SNO+, modest muon followers cuts reduce the cosmogenic background (11Be prompt + 11C delayed) to a negligible 7.0×10-4 ev/yr/kT • Spurious prompt events were used to produce “fake coincidences” with data events satisfying delayed event cuts • The 1.1% natural abundance of 13C in the organic scintillator can undergo a charged current interaction with neutrinos • The CC reaction on 13C has a threshold of 2.2 MeV and produces a 13N, which then decays • The coincidence nature of the event significantly reduces the background • Solar neutrinos produced in 8B decays from the pp chain in the Sun arrive at Earth with a flux of: