Results of a neutrino oscillation experiment performed at a meson factory beam-stop

This document describes a neutrino oscillation experiment performed at the Los Alamos Meson Physics Facility. The oscillation model searched for is bar νμ → bar νe. The first chapter is a review of the known properties of the neutrino and a description of the phenomenon of neutrino oscillation. Previous experimental limits on this unobserved phenomenon are also given. The second chapter describes the experimental apparatus used by the E645 experiment to detect neutrinos produced in the LAMPF beam stop. The salient features of the detector are its large mass (20 tons of CH2), its fine segmentation (to allow good particle tracking), good energy resolution, its recording of the history both before and after tracks appear in the detector, an active cosmic-ray anticoincidence shield, and 2000 gm/cm2 of passive cosmic-ray shielding. It is located 26.8 m from the neutrino source, which has a mean neutrino energy of 40 MeV. The third chapter details the reduction of the 1,3 million event data sample to a 49 event sample of neutrino candidates. Principle backgrounds are Michel electrons from stopping cosmic-ray muons and protons from np elastic scattering by cosmic-ray neutrons. The fourth chapter explains how background levels from neutrino-nuclear scattering are predicted. The result of maximum-likelihood analysis reveals no evidence for oscillation. 90% confidence levels are set at δm2 = .10 eV2 for large mixing and sin2(2θ) = .014 for large δm2