Neutrinoless Double Beta Decay with SNO+

1. Neutrinoless Double Beta Decay with SNO+ Jeff Hartnell for the SNO+ Collaboration University of Sussex, UK Neutrinoless Double Beta Decay (0νββ) Experiment Sensitivity With 780 tonnes of linear alkylbenzene (LAB), the SNO+ detector in Canada is one of the largest scintillator detectors in the world. Loading the scintillator with neodymium at a fraction of one percent by mass provides a tonne-scale experiment and a sensitive search for 0νββ will be performed. With 0.3% loading of natural neodymium SNO+ will contain 131 kg of 150Nd. Shown below is the simulated spectrum expected for an effective neutrino mass of 350 meV. • Discovery of 0νββ is of key importance for understanding the universe and would yield answers to fundamental questions. • Is the neutrino its own antiparticle? • What is the absolute mass of the neutrino? • With the violation of lepton number it is possible for two neutrons to simultaneously decay into two protons plus two electrons and no neutrinos. ~9500 PMTs, 54% coverage Acrylic vessel 12 m diameter The major backgrounds are from 2νββ and 8B solar neutrinos. 214Bi is shown with 99.98% tagging efficiency and 208Tl with 90%. SNO+ will be sensitive to 0νββ decays with a half-life of 1025 years and the evolution of the sensitivity to the effective neutrino mass is shown below. 780 tonnes LAB liquid scintillator 5700 tonnes H20 outer shielding The smallness of the neutrino mass suppresses the rate of this process but also gives a handle on that mass. The rate of 0νββ is given by O(tonne) 0νββ element/isotope 1700 tonnes H20 inner shielding National Geographic • Features of SNO+ • Trade off energy resolution for higher statistics. • Cost-effective since the detector already exists. • Various isotopes can be used. • Initial scintillator purification by distillation. • In-situ purification to further remove backgrounds. • Background reduction • Huge external shielding, 7400 tonnes. • PMTs stand-off from scintillator. • Self-shielding of the scintillator. where T1/2 is the half-life, G is the phase space factor, M is the nuclear matrix element and m is the electron/effective neutrino mass. The key experimental signature for 0νββ is a peak in visible energy at the Q-value of the nucleus, smeared by detector resolution. • Schedule • 2012: construct scintillator process systems, light water run. • 2013: scintillator phase begins. Avenues for future upgrades With R&D Nd enrichment and/or other isotopes offer potential for significant sensitivity gains.