Initial Results from the CHOOZ Long Baseline Reactor Neutrino Oscillation Experiment

TL;DR

The CHOOZ experiment investigated electron antineutrino oscillations over a 1 km baseline, finding no evidence for oscillations within the tested parameter space, and demonstrated the effectiveness of deep underground detectors in reducing background noise.

Contribution

First results from the CHOOZ reactor neutrino experiment providing constraints on neutrino oscillation parameters with a large, low-background liquid scintillation detector.

Findings

No evidence for neutrino oscillations at the tested parameters.

Achieved a background rate of about one event per day.

Set upper limits on oscillation parameters at 90% confidence level.

Abstract

Initial results are presented from CHOOZ, a long-baseline reactor-neutrino vacuum-oscillation experiment. Electron antineutrinos were detected by a liquid scintillation calorimeter located at a distance of about 1 km. The detector was constructed in a tunnel protected from cosmic rays by a 300 MWE rock overburden. This massive shielding strongly reduced potentially troublesome backgrounds due to cosmic-ray muons, leading to a background rate of about one event per day, more than an order of magnitude smaller than the observed neutrino signal. From the statistical agreement between detected and expected neutrino event rates, we find (at 90% confidence level) no evidence for neutrino oscillations in the electron antineutrino disappearance mode for the parameter region given approximately by deltam**2 > 0.9 10**(-3) eV**2 for maximum mixing and (sin(2 theta)**2) > 0.18 for large deltam**2.