Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment (1610.04802v1)

Abstract: A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GW${\rm th}$ nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of $\overline{\nu}{e}$'s. Comparison of the $\overline{\nu}{e}$ rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors ($\sim$1500-1950 m) relative to detectors near the reactors ($\sim$350-600 m) allowed a precise measurement of $\overline{\nu}{e}$ disappearance. More than 2.5 million $\overline{\nu}{e}$ inverse beta decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (Dec. 2011--Jul. 2012) with a subsequent 1013 days using the complete configuration of eight detectors (Oct. 2012--Jul. 2015). The $\overline{\nu}{e}$ rate observed at the far detectors relative to the near detectors showed a significant deficit, $R=0.949 \pm 0.002(\mathrm{stat.}) \pm 0.002(\mathrm{syst.})$. The energy dependence of $\overline{\nu}{e}$ disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle $\sin^22\theta{13}=0.0841 \pm 0.0027(\mathrm{stat.}) \pm 0.0019(\mathrm{syst.})$ and the effective neutrino mass-squared difference of $\left|{\Delta}m^2_{\mathrm{ee}}\right|=(2.50 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$. Analysis using the exact three-flavor probability found ${\Delta}m^2_{32}=(2.45 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ assuming the normal neutrino mass hierarchy and ${\Delta}m^2_{32}=(-2.56 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ for the inverted hierarchy.

Analyzing Electron Antineutrino Oscillation: Findings from the Daya Bay Experiment

The Daya Bay Reactor Neutrino Experiment provides an in-depth examination of electron antineutrino oscillations, drawing from extensive data collection over 1230 days. Utilizing six 2.9-GW$_{\rm th}$ nuclear reactors as intensive sources of electron antineutrinos, the experiment aimed to measure the disappearance rate by noting the energy spectrum differences between detectors proximal and distal to the reactor cores. With a vast number of inverse beta decay interactions—exceeding 2.5 million—captured across 217 and 1013 operational days with different detector configurations, the experiment significantly contributes to advancing our understanding of neutrino physics.

The observed interaction rates indicated a notable deficit at far detectors relative to near ones, with a ratio $$R=0.949 \pm 0.002(\mathrm{stat.}) \pm 0.002(\mathrm{syst.})$$. This data corroborates the phenomenon of electron antineutrino disappearance as predicted by oscillation models. Utilizing three-flavor oscillation probability analyses, the paper estimated the mixing angle $\sin^2 2 \theta_{13}$ and examined the effective neutrino mass-squared difference $\left|{\Delta}m^2_{\mathrm{ee}\right|$. The analyses yielded $$\sin^22\theta_{13} = 0.0841 \pm 0.0027\mathrm{(stat.)} \pm 0.0019\mathrm{(syst.)}$$ and $\left|{\Delta}m^2_{\mathrm{ee}\right| = \left[2.50 \pm 0.06\mathrm{(stat.)} \pm 0.06\mathrm{(syst.)}\right] \times 10^{-3}\, \text{eV}^2$.

Noteworthy is the experiment’s methodological robustness, comprising multiple statistical approaches to solidify findings and account for potential uncertainties in reactor antineutrino flux modeling, systematic detector responses, and other variants like background influences. By leveraging output from neutron spallation and reactor operations alongside comprehensive geometric and detector setup calibrations, the experiment minimizes variances among measurements, enhancing the precision of derived oscillation parameters.

Critically, the findings align with other empirical studies measuring neutrino oscillations via diverse methodologies—such as long baseline neutrino experiments—consolidating the three-flavor neutrino mass and mixing framework. The implications of Daya Bay's precise determinations extend to refining our comprehension of not only $\theta_{13}$ but also have vast implications for future explorations into the neutrino mass hierarchy and CP-violation studies. Continued enhancements in detector technology and methodology may further refine these measurements, promising deeper insights into the fundamental workings of particle physics.

Future endeavors should address identified systematic uncertainties, such as those related to the non-linearity of electron energy scales and potential variation in detector efficiencies, as these factors significantly shape the measurement of ${\Delta}m^2_{\mathrm{ee}$. As the field progresses, the integration of refined particle interaction models and augmented detective frameworks will likely drive even greater precision and understanding in neutrino physics. Such progress will necessitate robust statistical techniques paired with innovative technological applications to discern even subtler phenomena within this domain.