Neutrinoless Double Beta Decay with SNO+
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Neutrinoless Double Beta Decay with SNO+Jeff Hartnell for the SNO+ CollaborationUniversity of Sussex, UKAcrylic vessel12 m diameter780 tonnes LAB liquid scintillator5700 tonnes H20outer shielding1700 tonnes H20inner shielding~9500 PMTs, 54% coverageO(tonne) 0 element/isotopeExperimentNeutrinoless Double Beta Decay (0)SensitivityWith 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 0 will be performed.Schedule 2012: construct scintillator process systems, light water run. 2013: scintillator phase begins.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.
Discovery of 0 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.The smallness of the neutrino mass suppresses the rate of this process but also gives a handle on that mass. The rate of 0 is given by 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 0 is a peak in visible energy at the Q-value of the nucleus, smeared by detector resolution. 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.Avenues for future upgradesWith R&D Nd enrichment and/or other isotopes offer potential for significant sensitivity gains.The major backgrounds are from 2 and 8B solar neutrinos. 214Bi is shown with 99.98% tagging efficiency and 208Tl with 90%.
SNO+ will be sensitive to 0 decays with a half-life of 1025 years and the evolution of the sensitivity to the effective neutrino mass is shown below.