Search For Invisible Nucleon Decay in SNO+ With Improved Sensitivity
The water phase of the SNO+ (Sudbury Neutrino Observatory) experiment has completed after the collection of ~305 days of total livetime worth of data, divided into two main sets. The effective concentration of U-238 and Th-232 in the water was determined using in situ analysis to be, for the second set of data, gU/gH2O: (3.64 +/- 0.74_(stat) + 1.28_(syst) - 0.99_(syst) x 10^-15 and gTh/gH2O: (3.08 +/- 3.22_(stat) + 1.60_(syst) - 5.00_(syst) ) x 10^-16. The water data can also been used to search for ``invisible" modes of nucleon decay, and a previous SNO+ publication set world-leading limits on relevant nucleon and dinucleon decay modes except neutron and dineutron decay. This thesis presents a re-analysis of the ``invisible" neutron decay mode of that first set of data, which reoptimizes the fiducial volume and develops an improved treatment of the dominant energy systematic uncertainties. This leads to a world-leading lower limit on the ``invisible" neutron decay lifetime of 6.91 x 10^29 years. A sensitivity analysis shows that including the second set of data that has lower backgrounds is expected to yield a lower limit on the neutron decay lifetime of 1.57 x 10^30 years, further improving the result.
URI for this recordhttp://hdl.handle.net/1974/28238
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