Experimental HEP Seminar

Extraction of Active and Sterile Neutrino Mixing Parameters with the Sudbury Neutrino Observatory

Gordana Tešić

Physics Department
Carleton University

The Sudbury Neutrino Observatory (SNO) is a 1 kilotonne heavy-water Čerenkov detector designed to study fundamental properties of neutrinos produced by thermonuclear fusion reactions in the core of the Sun. The SNO measurements of the Neutral-Current (NC) and Charged-Current (CC) fluxes for neutrinos originated from ⁸B disintegration inside the Sun unambiguously proved that neutrinos change their flavour while traveling to the Earth. The interpretation of solar neutrino data from SNO and other experiments, in the frameworks of the two distinct neutrino mixing models, is presented. Under the assumption on the two-neutrino oscillation hypothesis, mixing parameters for active neutrinos (the squared-mass difference Δm² and the mixing angle θ) are obtained from a global analysis of solar and reactor neutrino data. The result obtained represents the newest measurement from SNO. It further improves the SNO measurement on the solar neutrino mixing parameters by reducing the allowed region in the neutrino mixing parameter space. The mixing parameters for the sterile neutrino state (the ratio R_Δ = Δm²₀₁ /Δm²₂₁ and the mixing angle sin² 2α) are determined by comparing the predictions from a weakly mixed sterile neutrino model with the solar neutrino data. For the first time a complete parameter region for the weakly mixed sterile state is fully scanned numerically to place the error on R_Δ and to set an upper limit at 90% CL on sin² 2α. The result reported shows that the rare effects from physics beyond the three active neutrino scenario cannot be excluded, yet. Future prospects and challenge in solar neutrino physics are also summarized.