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 6.9×10^{5} GW_{th}  ton 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}Am-^{13}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}2θ_{13} and |Δm_{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}2θ_{13}=0.084±0.005 and |Δm_{ee}^{2}|=(2.42±0.11)×10^{-3}  eV^{2} in the three-neutrino framework.

This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GWth 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 β decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55±0.04) ×10(-18)  cm(2) GW(-1) day(-1) or (5.92±0.14) ×10(-43)  cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946±0.022 (0.991±0.023) relative to the flux predicted with the Huber-Mueller (ILL-Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2σ over the full energy range with a local significance of up to ∼4σ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.

The Daya Bay experiment consists of functionally identical antineutrino detectors immersed in pools of ultrapure water in three well-separated underground experimental halls near two nuclear reactor complexes. These pools serve both as shields against natural, low-energy radiation, and as water Cherenkov detectors that efficiently detect cosmic muons using arrays of photomultiplier tubes. Each pool is covered by a plane of resistive plate chambers as an additional means of detecting muons. Design, construction, operation, and performance of these muon detectors are described.

A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2)<|Δm(41)(2) |< 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2θ(14) cover the 10(-3) eV(2) ≲ |Δm(41)(2)| ≲ 0.1 eV(2) region, which was largely unexplored.

A measurement of the energy dependence of antineutrino disappearance at the Daya Bay reactor neutrino experiment is reported. Electron antineutrinos (ν¯(e)) from six 2.9  GW(th) reactors were detected with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls. Using 217 days of data, 41 589 (203 809 and 92 912) antineutrino candidates were detected in the far hall (near halls). An improved measurement of the oscillation amplitude sin(2)2θ(13)=0.090(-0.009)(+0.008) and the first direct measurement of the ν¯(e) mass-squared difference |Δm(ee)2|=(2.59(-0.20)(+0.19))×10(-3)  eV2 is obtained using the observed ν¯(e) rates and energy spectra in a three-neutrino framework. This value of |Δm(ee)2| is consistent with |Δm(μμ)2| measured by muon neutrino disappearance, supporting the three-flavor oscillation model.

A new measurement of the $\theta_{13}$ mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of $\theta_{13}$ measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GW$_{th}$ reactors, the rate deficit observed at the far hall is interpreted as $\sin^22\theta_{13}=0.083\pm0.018$ in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain $\sin^22\theta_{13}=0.089\pm0.008$ as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.

With 1.06 × 108 ψ(3686) events collected with the BESIII detector, the branching fraction of ψ (3686) → ωK+K- is measured to be (1.54 ± 0.04 ± 0.11) × 10-4. This is the most precise result to date, due to the largest ψ(3686) sample, improved signal reconstruction efficiency, good simulation of the detector performance, and a more accurate knowledge of the continuum contribution. Using the branching fraction of J/ψ → ωK+K-, the ratio β(ψ(3868) → ωK+K-)/β(J/ψ → ωK+K-) is determined to be (18.4 ± 3.7)%. This constitutes a significantly improved test of the 12% rule, with the uncertainty now dominated by the J/ψ branching fraction.

We report a measurement of the branching fraction B(D+→μ+νμ)= [3.71±0.19(stat)±0.06(sys)]×10-4 based on 2.92fb-1 of data accumulated at s=3.773GeV with the BESIII detector at the BEPCII collider. This measurement, in conjunction with the Cabibbo-Kobayashi-Maskawa matrix element |Vcd| determined from a global Standard Model fit, implies a value for the weak decay constant fD+=(203.2±5.3±1.8)MeV. Additionally, using this branching fraction measurement together with a lattice QCD prediction for fD+, we find |Vcd|=0.2210±0.0058±0.0047. In either case, these are the most precise results for these quantities to date.

A search for the rare decays of J/ψ → Dsρ+ + c.c. and J/ψ → D0K∗0 + c.c. is performed with a data sample of 225.3-million J/ψ events collected with the Beijing Spectrometer III detector. No evident signal is observed. Upper limits on the branching fractions are determined to be B(J/ψ → Ds ρ+ + c.c.) < 1.3 × 10-5 and B(J/ψ → D0K ∗0+ c.c.) < 2.5 × 10-6 at the 90% confidence level.

By using a 2.92 fb-1 data sample taken at √s = 3.773 GeV with the BESIII detector operating at the BEPCII collider, we search for the radiative transitions ψ(3770) → γηc and γηc(2S) through the hadronic decays ηc(ηc (2S)) → K0SK±π+. No significant excess of signal events above background is observed. We set upper limits at a 90% confidence level for the product branching fractions to be B(ψ(3770) →γηc) ±B(ηc → K0SK±π+) < 1.6× 10-5 and B(ψ(3770) →γηc(2S)) ×B(ηc(2S) → K0SK+π+) <5.6× 10-6. Combining our result with world-average values of B(ηc(ηc(2S)) → K0SK±π+), we find the branching fractions B(ψ(3770) → γηc) > 6.8 × 10-4 and B(ψ(3770) → γηc(2S)) < 2.0 × 10-3 at a 90% confidence level.