A treatise on high energy muons in the IMB detector

Abstract

The Irvine-Michigan-Brookhaven proton decay detector records upward-going muon data at a rate of ~0.5 μ/day and downward-going muon data at a rate of 2.7 μ/s. After separating the upward-going data from the downward-going data, both data sets are examined for consistency with expectation and searched for physical effects. The upward-going muon data is used to search for vμ ↔ ve and vμ ↔ vT neutrino oscillation effects that are consistent with the parameters suggested by the atmospheric neutrino flavor anomaly that is found in the contained data. Three different techniques provide the search, but uncover no evidence. Hence, the upward-going data limits the preferred parameter space for both types of oscillations. For vμ ↔ ve oscillations, the 90% C.L. limits are sin^(2)2θ ≥ 0.38 for large δm^2 and δm^2 ≥ 1.8 x 10^-2 at large mixing angles, while the limits for vμ ↔ vT oscillations are sin^(2)2θ ≥ 0.42 for large δm^2 and δm^2 ≥ 1.7 x 10^-3 at large mixing angles. Although the upward-going data remains consistent with the neutrino oscillation hypothesis, it greatly limits the possible parameters. In addition to the neutrino oscillation analysis, the downward-going muon data is used to search for point sources and to study the origins of underground muons. Although the testing of 13 sources chosen a priori uncovered no candidates, two features stand out in these data: at least two possible point sources and a large scale anisotropy. A survey of the entire sky finds two excesses at IMBm1=(α ~ 164°, δ ~ 53°) and IMBm2=(α ~ 106°, δ ~ 68°), with random chance probabilities (including trials penalties) of p = 2.0 X 10^-5 and p = 7.9 X 10^-4 respectively, although neither direction is associated with any popular v or -y-ray sources. In addition, there is an anisotropy in the data favoring the α = 270° and δ = 30° direction, with an approximate magnitude of 10^-2. This magnitude is surprisingly large, but it does not seem to be attributable to systematics in the data.