The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of $0.944\pm 0.016(\mathrm{stat})\pm 0.040(\mathrm{syst})$ was obtained in 101 days of running at the Chooz nuclear power plant in France, with two $4.25{\mathrm{GW}}_{\mathrm{th}}$ reactors. The results were obtained from a single $10{\mathrm{m}}^3$ fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter ${sin}^{2}2{\theta }_{13}$. Analyzing both the rate of the prompt positrons and their energy spectrum, we find ${sin}^{2}2{\theta }_{13}=0.086\pm 0.041(\mathrm{stat})\pm 0.030(\mathrm{syst})$, or, at 90% C.L., $0.017<{sin}^{2}2{\theta }_{13}<0.16$.

We report on a search for neutrinoless double-beta decay of ${}^{136}\mathrm{Xe}$ with EXO-200. No signal is observed for an exposure of 32.5 kg yr, with a background of $\sim 1.5\times {10}^{-3}{\mathrm{kg}}^{-1}{\mathrm{yr}}^{-1}{\mathrm{keV}}^{-1}$ in the $\pm 1\sigma$ region of interest. This sets a lower limit on the half-life of the neutrinoless double-beta decay $T_{1/2}^{0\nu \beta \beta }({}^{136}\mathrm{Xe})>1.6\times {10}^{25}\mathrm{yr}$ (90% C.L.), corresponding to effective Majorana masses of less than 140–380 meV, depending on the matrix element calculation.

A search for neutrinoless double-$\beta$ decay ($0\nu \beta \beta$) in ${}^{136}\mathrm{Xe}$ is performed with the full EXO-200 dataset using a deep neural network to discriminate between $0\nu \beta \beta$ and background events. Relative to previous analyses, the signal detection efficiency has been raised from 80.8% to $96.4\pm 3.0\%$, and the energy resolution of the detector at the $Q$ value of ${}^{136}\mathrm{Xe}$ $0\nu \beta \beta$ has been improved from $\sigma /E=1.23\%$ to $1.15\pm 0.02\%$ with the upgraded detector. Accounting for the new data, the median 90% confidence level $0\nu \beta \beta$ half-life sensitivity for this analysis is $5.0\times {10}^{25}\mathrm{yr}$ with a total ${}^{136}\mathrm{Xe}$ exposure of 234.1 kg yr. No statistically significant evidence for $0\nu \beta \beta$ is observed, leading to a lower limit on the $0\nu \beta \beta$ half-life of $3.5\times {10}^{25}\mathrm{yr}$ at the 90% confidence level.

The Double Chooz experiment has observed 8249 candidate electron antineutrino events in 227.93 live days with 33.71 GW-ton-years ($\mathrm{\text{reactor power}}\times \mathrm{\text{detector mass}}\times \mathrm{\text{live time}}$) exposure using a $10.3{\mathrm{m}}^3$ fiducial volume detector located at 1050 m from the reactor cores of the Chooz nuclear power plant in France. The expectation in case of ${\theta }_{13}=0$ is 8937 events. The deficit is interpreted as evidence of electron antineutrino disappearance. From a rate plus spectral shape analysis we find ${sin}^{2}2{\theta }_{13}=0.109\pm 0.030(\mathrm{stat})\pm 0.025(\mathrm{syst})$. The data exclude the no-oscillation hypothesis at 99.8% CL ($2.9\sigma$).

The next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double-$\beta$ ($0\nu \beta \beta$) decay in ${}^{136}\mathrm{Xe}$ with a target half-life sensitivity of approximately ${10}^{28}$ yr using $5\times {10}^3$ kg of isotopically enriched liquid-xenon in a time projection chamber. This improvement of two orders of magnitude in sensitivity over current limits is obtained by a significant increase of the ${}^{136}\mathrm{Xe}$ mass, the monolithic and homogeneous configuration of the active medium, and the multiparameter measurements of the interactions enabled by the time projection chamber. The detector concept and anticipated performance are presented based upon demonstrated realizable background rates.

Results from a search for neutrinoless double-beta decay ($0\nu \beta \beta$) of ${}^{136}\mathrm{Xe}$ are presented using the first year of data taken with the upgraded EXO-200 detector. Relative to previous searches by EXO-200, the energy resolution of the detector has been improved to $\sigma /E=1.23\%$, the electric field in the drift region has been raised by 50%, and a system to suppress radon in the volume between the cryostat and lead shielding has been implemented. In addition, analysis techniques that improve topological discrimination between $0\nu \beta \beta$ and background events have been developed. Incorporating these hardware and analysis improvements, the median 90% confidence level $0\nu \beta \beta$ half-life sensitivity after combining with the full data set acquired before the upgrade has increased twofold to $3.7\times {10}^{25}\mathrm{yr}$. No statistically significant evidence for $0\nu \beta \beta$ is observed, leading to a lower limit on the $0\nu \beta \beta$ half-life of $1.8\times {10}^{25}\mathrm{yr}$ at the 90% confidence level.