Search for neutrino oscillations on a long base-line at the CHOOZ nuclear power station

TL;DR

The CHOOZ experiment delivers a precise, multi-faceted test of electron antineutrino disappearance from nuclear reactors over a long baseline. By meticulously characterizing the $\overline{\nu}_{e}$ source, deploying a Gd-loaded scintillator detector with robust calibration and reconstruction, and applying three complementary oscillation analyses, the study derives stringent constraints on $\sin^2 2\theta$ and $\delta m^2$—notably excluding large $\nu_e$ mixing in the atmospheric mass-squared range. The work also introduces a novel, systematics-aware method for confidence-region derivation, illustrating improved handling of uncertainties in neutrino-oscillation studies. Collectively, the results favor $\nu_\mu \rightarrow \nu_\tau$ as the dominant atmospheric oscillation channel and provide critical inputs for global fits of three-flavour mixing. The methods and findings strengthen reactor-based oscillation limits and illuminate the role of detector-systematics in high-precision neutrino experiments.

Abstract

This final article about the CHOOZ experiment presents a complete description of the electron antineutrino source and detector, the calibration methods and stability checks, the event reconstruction procedures and the Monte Carlo simulation. The data analysis, systematic effects and the methods used to reach our conclusions are fully discussed. Some new remarks are presented on the deduction of the confidence limits and on the correct treatment of systematic errors.

Figures (58)

• Figure 1: Voltmeter calibration for reactor 1 (left) and 2 (right).
• Figure 2: Schematic view of the fuel rods in the core for the first cycle of the CHOOZ reactors. The number of Boron poison rods assembled with each fuel element is also indicated.
• Figure 3: Power distribution and burn-up values for the fuel elements in an octant of the CHOOZ reactor core at a certain step ($\beta =1000$ of the first cycle). The contribution to the power of each element is normalized to have a mean value equal to one.
• Figure 4: Neutrino yield per fission of the listed isotopes, as determined by converting the measured $\beta$ spectra Schreck2Schreck3.
• Figure 5: Comparison of Bugey 3 data with three different reactor spectrum models. The error bars include only statistical uncertainties. The dashed lines are the quadratic sum of the quoted error of the models and the error due to the energy calibration.