A Precision Measurement of the Neutrino Mixing Angle theta_13 using Reactor Antineutrinos at Daya Bay

TL;DR

The Daya Bay proposal outlines a precision reactor antineutrino experiment to measure the mixing angle $\theta_{13}$ with sensitivity $\sin^2 2\theta_{13} \lesssim 0.01$ at 90% CL by deploying multiple identical detectors at near and far sites surrounding the Daya Bay/Ling Ao reactor complex. The design leverages three-zone, gadolinium-doped liquid scintillator detectors, a water-Cherenkov muon system, and rigorous calibration/monitoring to minimize reactor-, detector-, and background-related systematics, achieving sub-percent relative uncertainties between detectors. A global $\chi^2$ analysis incorporating correlated systematics predicts strong sensitivity to $\theta_{13}$, enabling a clean separation from CP-violating effects and matter-induced hierarchies in future experiments. The document details the experimental layout, detector and muon systems, calibration strategies, site/civil construction plans, and the roadmap for achieving the targeted precision over a multi-year running period. The work emphasizes near-far detector comparisons, detector swapping/cross-calibration, and comprehensive background control as the key to reaching the ambitious measurement goal.

Abstract

A reactor-neutrino experiment, Daya Bay, has been proposed to determine the least-known neutrino mixing angle theta_13 using electron antineutrinos produced at the Daya Bay nuclear power complex in China. Daya Bay is an international collaboration with institutions from China, the United States, the Czech Republic, Hong Kong, Russia, and Taiwan. The experiment will use eight identical detectors deployed at three different locations optimized for monitoring the antineutrino rates from the six reactors and for detecting any rate deficit and spectral distortion near the first oscillation maximum. The overburden of the under ground experimental halls, connected with tunnels, ranges from about 250 to 900 meters-water-equivalent so that the cosmogenic background is small compared to the number of observed antineutrino events. Civil construction of tunnels and experimental facilities is planned to start in 2007, with detector construction beginning in 2008. The experiment will begin collecting data in 2010. By comparing the detected signals at the three locations, with three years of data, a sensitivity in sin**2(2theta_13) of better than 0.01 is expected.

Figures (108)

• Figure 1: Default configuration of the Daya Bay experiment, optimized for best sensitivity in sin$^22\theta_{13}$. Four detector modules are deployed at the far site and two each at each of the near sites.
• Figure 1.1: Global fits to $\sin^2\theta_{13}$, taken from Fogli.
• Figure 1.2: Resolving ambiguity in $\theta_{23}$ with $\sin^22\theta_{13}$ determined by reactor experiments. Not only does the reactor experiment provide a precise measurement of $\sin^22\theta_{13}$, but it provides a precise measurement of $\theta_{23}$ by resolving an ambiguity in the interpretation of the accelerator data. The blue line is the 95% C.L. curve averaged over the two mass-hierarchy solutions and possible values of $\delta_{CP}$.
• Figure 1.3: Fission rate of reactor isotopes as a function of time from a Monte Carlo simulation 3miller.
• Figure 1.4: Yield of antineutrinos per fission for the several isotopes. These are determined by converting the corresponding measured $\beta$ spectra 3illbeta.