A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GWth 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 ($\sim 1500–1950\mathrm{m}$) relative to detectors near the reactors ($\sim 350–600\mathrm{m}$) 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 (December, 2011–July, 2012) with a subsequent 1013 days using the complete configuration of eight detectors (October, 2012–July, 2015). The ${\overline{\nu }}_e$ rate observed at the far detectors relative to the near detectors showed a significant deficit, $R=0.949\pm 0.002(\text{stat})\pm 0.002(\text{syst})$. 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 ${\sin }^{2}2{\theta }_{13}=0.0841\pm 0.0027(\text{stat})\pm 0.0019(\text{syst})$ and the effective neutrino mass-squared difference of $|\mathrm{\Delta }{m}_{\mathrm{ee}}^2|=(2.50\pm 0.06(\text{stat})\pm 0.06(\text{syst}))\times {10}^{-3}{\mathrm{eV}}^2$. Analysis using the exact three-flavor probability found $\mathrm{\Delta }{m}_{32}^2=(2.45\pm 0.06(\text{stat})\pm 0.06(\text{syst}))\times {10}^{-3}{\mathrm{eV}}^2$ assuming the normal neutrino mass hierarchy and $\mathrm{\Delta }{m}_{32}^2=(-2.56\pm 0.06(\text{stat})\pm 0.06(\text{syst}))\times {10}^{-3}{\mathrm{eV}}^2$ for the inverted hierarchy.

This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 ${\mathrm{GW}}_{\mathrm{t}\mathrm{h}}$ nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296 721 and 41 589 inverse $\beta$ decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is ($1.55\pm 0.04$) $\times {10}^{-18}{\mathrm{cm}}^2{\mathrm{GW}}^{-1}{\text{day}}^{-1}$ or ($5.92\pm 0.14$) $\times {10}^{-43}{\mathrm{cm}}^2{\text{fission}}^{-1}$. This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is $0.946\pm 0.022$ ($0.991\pm 0.023$) relative to the flux predicted with the $\mathrm{Huber}\text{−}\mathrm{Mueller}$ ($\mathrm{ILL}\text{-Vogel}$) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than $2\sigma$ over the full energy range with a local significance of up to $\sim 4\sigma$ between 4–6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.

A search for the solar neutrino effective magnetic moment has been performed using data from 1291.5 days exposure during the second phase of the Borexino experiment. No significant deviations from the expected shape of the electron recoil spectrum from solar neutrinos have been found, and a new upper limit on the effective neutrino magnetic moment of ${\mu }_{\nu }^{\mathrm{eff}}<{2.8\times 10}^{-11}$ ${\mu }_B$ at 90% C.L. has been set using constraints on the sum of the solar neutrino fluxes implied by the radiochemical gallium experiments. Using the limit for the effective neutrino moment, new limits for the magnetic moments of the neutrino flavor states, and for the elements of the neutrino magnetic moments matrix for Dirac and Majorana neutrinos, are derived.

We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of $6.9\times {10}^5$ ${\mathrm{GW}}_{\text{th}}\mathrm{ton}\mathrm{days}$, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six ${}^{241}\mathrm{Am}\text{−}{}^{13}\mathrm{C}$ radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of ${\sin }^{2}2{\theta }_{13}$ and $|\mathrm{\Delta }{m}_{ee}^2|$ were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave ${\sin }^{2}2{\theta }_{13}=0.084\pm 0.005$ and $|\mathrm{\Delta }{m}_{ee}^2|=(2.42\pm 0.11)\times {10}^{-3}{\mathrm{eV}}^2$ in the three-neutrino framework.