Observation of electron-antineutrino disappearance at Daya Bay (1203.1669v2)

Abstract: The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for the neutrino mixing angle $\theta_{13}$ with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GW${\rm th}$ reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43,000 ton-GW{\rm th}-day livetime exposure in 55 days, 10416 (80376) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is $R=0.940\pm 0.011({\rm stat}) \pm 0.004({\rm syst})$. A rate-only analysis finds $\sin^22\theta_{13}=0.092\pm 0.016({\rm stat})\pm0.005({\rm syst})$ in a three-neutrino framework.

• The paper presents a precise measurement of electron-antineutrino disappearance using six detectors in a near-far configuration.
• Methodologies include robust statistical and systematic uncertainty control to accurately determine the oscillation parameter θ13.
• Results confirm a nonzero mixing angle with sin²(2θ13)=0.092±0.016 (stat)±0.005 (syst), excluding the no-oscillation hypothesis at 5.2σ.

Overview of the Daya Bay Experiment: Electron-Antineutrino Disappearance and Neutrino Mixing

The paper "Observation of electron-antineutrino disappearance at Daya Bay" reports an important measurement from the Daya Bay Reactor Neutrino Experiment, providing insights into the electron-antineutrino oscillation and the precise measurement of the neutrino mixing angle $\theta_{13}$. This experiment stands out for its strategic deployment of operationally identical antineutrino detectors in a near-far configuration, enabling a precise measurement essential for verifying theoretical predictions within the standard neutrino oscillation framework.

Experimental Configuration and Data Collection

The experimentation utilized six electron-antineutrino detectors (ADs) in three underground experimental halls, strategically positioned to measure antineutrinos originating from six nuclear reactors at Daya Bay. The divisions included two near experimental halls (EH1 and EH2) and one far experimental hall (EH3), giving varied flux-weighted baselines that are pivotal for observing oscillation effects. The objective was to observe the deficit of electron-antineutrinos at varied distances and infer the mixing angle $\theta_{13}$ through the survival probability relation of electron-antineutrinos, expressed as $$P_{\text{sur}} \approx 1 - \sin^2(2\theta_{13})\sin^2(1.267\Delta m^2_{31}L/E)$$.

Observations and Results

The experiment reports the detection of 10,416 electron antineutrino candidates in the far hall over 55 days, compared to 80,376 events in the near halls. Analysis of the data, incorporating statistical and systematic uncertainty considerations, yields a $\sin^2(2\theta_{13})$ value of $$0.092 \pm 0.016 \text{{ (stat)}} \pm 0.005 \text{{ (syst)}}$$, excluding the no-oscillation hypothesis at 5.2 standard deviations. These results confirm that the mixing angle $\theta_{13}$ is non-zero, a conclusion supported by prior indications from the T2K, MINOS, and Double Chooz experiments, but achieved here with notable precision.

Methodology

The approach involved relative measurement leveraging the near-far detector setup to compare observed ratios. This configuration effectively mitigates correlated uncertainties and reactor-related uncertainties. The paper rigorously handles systematic uncertainties, capturing contributions from natural and instrumental backgrounds, data acquisition live time, and energy calibration, with muon veto efficiency calculated at each detector.

Implications and Future Considerations

The precise measurement of the mixing angle $\theta_{13}$ enhances the understanding of the neutrino oscillation phenomenon, facilitating refined models of particle physics beyond the standard model. The experimental methodology, particularly the strategic deployment of detectors and the robust analysis of statistical and systematic uncertainties, sets a benchmark for future neutrino experiments.

Further, such experiments' outcomes have broader implications, potentially influencing the design and operation of next-generation neutrino observatories aiming to resolve outstanding questions, such as the neutrino mass hierarchy and CP violation in the lepton sector. These advancements are crucial for the evolving landscape of particle physics, requiring continued exploration and integration of experimental data with theoretical models.