Search for Trilepton Nucleon Decay via $p\to e^{+}\nu \nu$ and $p\to {\mu }^{+}\nu \nu$ in the Super-Kamiokande Experiment

The trilepton nucleon decay modes $p\to e^{+}\nu \nu$ and $p\to {\mu }^{+}\nu \nu$ violate $|\mathrm{\Delta }(B-L)|$ by two units. Using data from a 273.4 kt yr exposure of Super-Kamiokande a search for these decays yields a fit consistent with no signal. Accordingly, lower limits on the partial lifetimes of ${\tau }_{p\to e^{+}\nu \nu }>1.7\times 10^{32}$ years and ${\tau }_{p\to {\mu }^{+}\nu \nu }>2.2\times 10^{32}$ years at a 90% confidence level are obtained. These limits can constrain Grand Unified Theories which allow for such processes.

Figure 1

Reconstructed momentum distribution for 273.4 kt yr of combined SK data (black dots), the best fit result for the atmospheric neutrino background and signal Monte Carlo simulation (solid line) as well as the 90% confidence level allowed amount of nucleon decay (hatched histogram) for $p\to e^{+}\nu \nu$ (left) and $p\to {\mu }^{+}\nu \nu$ (right). Residuals from data after background subtraction (bottom histograms).