Search

The disappearance of reactor $\bar{\nu}_e$ observed by the Daya Bayexperiment is examined in the framework of a model in which the neutrino isdescribed by a wave packet with a relative intrinsic momentum dispersion$\sigma_\text{rel}$. Three pairs of nuclear reactors and eight antineutrinodetectors, each with good energy resolution, distributed among threeexperimental halls, supply a high-statistics sample of $\bar{\nu}_e$ acquiredat nine different baselines. This provides a unique platform to test theeffects which arise from the wave packet treatment of neutrino oscillation. Themodified survival probability formula was used to fit Daya Bay data, providingthe first experimental limits: $2.38 \cdot 10^{-17} < \sigma_{\rm rel} < 0.23$.Treating the dimensions of the reactor cores and detectors as constraints, thelimits are improved: $10^{-14} \lesssim \sigma_{\rm rel} < 0.23$, and an upperlimit of $\sigma_{\rm rel}

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 νe's. Comparison of the νe rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors (∼1500-1950 m) relative to detectors near the reactors (∼350-600 m) allowed a precise measurement of νe disappearance. More than 2.5 million νe 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 νe rate observed at the far detectors relative to the near detectors showed a significant deficit, R=0.949±0.002(stat)±0.002(syst). The energy dependence of νe disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle sin22θ13=0.0841±0.0027(stat)±0.0019(syst) and the effective neutrino mass-squared difference of |Δmee2|=(2.50±0.06(stat)±0.06(syst))×10-3 eV2. Analysis using the exact three-flavor probability found Δm322=(2.45±0.06(stat)±0.06(syst))×10-3 eV2 assuming the normal neutrino mass hierarchy and Δm322=(-2.56±0.06(stat)±0.06(syst))×10-3 eV2 for the inverted hierarchy.

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 νe's. Comparison of the νe rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors (∼1500-1950 m) relative to detectors near the reactors (∼350-600 m) allowed a precise measurement of νe disappearance. More than 2.5 million νe 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 νe rate observed at the far detectors relative to the near detectors showed a significant deficit, R=0.949±0.002(stat)±0.002(syst). The energy dependence of νe disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle sin22θ13=0.0841±0.0027(stat)±0.0019(syst) and the effective neutrino mass-squared difference of |Δmee2|=(2.50±0.06(stat)±0.06(syst))×10-3 eV2. Analysis using the exact three-flavor probability found Δm322=(2.45±0.06(stat)±0.06(syst))×10-3 eV2 assuming the normal neutrino mass hierarchy and Δm322=(-2.56±0.06(stat)±0.06(syst))×10-3 eV2 for the inverted hierarchy.

A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GWth nuclear reactors and detected by eight antineutrino detectors deployed in two near (560 m and 600 m flux-weighted baselines) and one far (1640 m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be 0.946±0.020 (0.992±0.021) for the Huber+Mueller (ILL+Vogel) model. A 2.9σ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6 MeV was found in the measured spectrum, with a local significance of 4.4σ. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.

A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GWth nuclear reactors and detected by eight antineutrino detectors deployed in two near (560 m and 600 m flux-weighted baselines) and one far (1640 m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be 0.946±0.020 (0.992±0.021) for the Huber+Mueller (ILL+Vogel) model. A 2.9σ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6 MeV was found in the measured spectrum, with a local significance of 4.4σ. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.

This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the 2×10^{-4}≲|Δm_{41}^{2}|≲0.3  eV^{2} mass range. The resulting limits on sin^{2}2θ_{14} are improved by approx imately a factor of 2 over previous results and constitute the most stringent constraints to date in the |Δm_{41}^{2}|≲0.2  eV^{2} region.

Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on sin^{2}2θ_{μe} are set over 6 orders of magnitude in the sterile mass-squared splitting Δm_{41}^{2}. The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for Δm_{41}^{2}

Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on sin^{2}2θ_{μe} are set over 6 orders of magnitude in the sterile mass-squared splitting Δm_{41}^{2}. The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for Δm_{41}^{2}

This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the 2×10^{-4}≲|Δm_{41}^{2}|≲0.3  eV^{2} mass range. The resulting limits on sin^{2}2θ_{14} are improved by approx imately a factor of 2 over previous results and constitute the most stringent constraints to date in the |Δm_{41}^{2}|≲0.2  eV^{2} region.

This article reports an improved independent measurement of neutrino mixing angle θ13 at the Daya Bay Reactor Neutrino Experiment. Electron antineutrinos were identified by inverse β-decays with the emitted neutron captured by hydrogen, yielding a data set with principally distinct uncertainties from that with neutrons captured by gadolinium. With the final two of eight antineutrino detectors installed, this study used 621 days of data including the previously reported 217-day data set with six detectors. The dominant statistical uncertainty was reduced by 49%. Intensive studies of the cosmogenic muon-induced Li9 and fast neutron backgrounds and the neutron-capture energy selection efficiency, resulted in a reduction of the systematic uncertainty by 26%. The deficit in the detected number of antineutrinos at the far detectors relative to the expected number based on the near detectors yielded sin22θ13=0.071±0.011 in the three-neutrino-oscillation framework. The combination of this result with the gadolinium-capture result is also reported.

This article reports an improved independent measurement of neutrino mixing angle θ13 at the Daya Bay Reactor Neutrino Experiment. Electron antineutrinos were identified by inverse β-decays with the emitted neutron captured by hydrogen, yielding a data set with principally distinct uncertainties from that with neutrons captured by gadolinium. With the final two of eight antineutrino detectors installed, this study used 621 days of data including the previously reported 217-day data set with six detectors. The dominant statistical uncertainty was reduced by 49%. Intensive studies of the cosmogenic muon-induced Li9 and fast neutron backgrounds and the neutron-capture energy selection efficiency, resulted in a reduction of the systematic uncertainty by 26%. The deficit in the detected number of antineutrinos at the far detectors relative to the expected number based on the near detectors yielded sin22θ13=0.071±0.011 in the three-neutrino-oscillation framework. The combination of this result with the gadolinium-capture result is also reported.

The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of ν¯e oscillations over km-baselines. Subsequent data has provided the world's most precise measurement of sin22θ13 and the effective mass splitting Δmee2. The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world's most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.

The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of ν¯e oscillations over km-baselines. Subsequent data has provided the world's most precise measurement of sin22θ13 and the effective mass splitting Δmee2. The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world's most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.

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.

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.

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.

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.

BACKGROUND: Ethnic minorities, especially African Americans and Latinos, bear a disproportionate burden of colorectal cancer (CRC), as reflected in incidence, cancer stage, and mortality statistics. In all ethnic groups, first-degree relatives (FDRs) of CRC cases are at an elevated disease risk. However, underuse of CRC screening persists and is particularly evident among minority groups. The current study tested a stepped intervention to increase CRC screening among an ethnically diverse sample of FDRs of CRC cases. METHODS: A statewide cancer registry was used to recruit CRC cases and through them their FDRs. Relatives who were not current on CRC screening were randomized to intervention or usual-care control arms. The stepped intervention consisted of ethnically targeted and individually tailored print materials followed by telephone counseling for those unscreened at 6 months. RESULTS: The study sample of 1280 individuals consisted of 403 Latino, 284 African American, 242 Asian, and 351 white FDRs. Statistically significant effects were observed for the cumulative print plus telephone intervention at 12 months (26% in the intervention vs 18% in the control group) and the print intervention alone at 6 months (15% in the intervention vs 10% in the control group). The effect of the print intervention alone versus the cumulative interventions was not statistically significantly different. Stratified analyses indicated that the intervention was effective among white, Latino, and Asian individuals, but not among African-Americans. CONCLUSIONS: Overall, the intervention was effective in increasing screening rates. Oversampling racial/ethnic minorities allowed for the examination of effects within subgroups, revealing no effect among African American individuals. This finding illustrates the importance of including sufficient numbers of participants from diverse ethnic subgroups in intervention research to enable such stratified analyses. Cancer 2015;121:2951-2959.

BACKGROUND: Ethnic minorities, especially African Americans and Latinos, bear a disproportionate burden of colorectal cancer (CRC), as reflected in incidence, cancer stage, and mortality statistics. In all ethnic groups, first-degree relatives (FDRs) of CRC cases are at an elevated disease risk. However, underuse of CRC screening persists and is particularly evident among minority groups. The current study tested a stepped intervention to increase CRC screening among an ethnically diverse sample of FDRs of CRC cases. METHODS: A statewide cancer registry was used to recruit CRC cases and through them their FDRs. Relatives who were not current on CRC screening were randomized to intervention or usual-care control arms. The stepped intervention consisted of ethnically targeted and individually tailored print materials followed by telephone counseling for those unscreened at 6 months. RESULTS: The study sample of 1280 individuals consisted of 403 Latino, 284 African American, 242 Asian, and 351 white FDRs. Statistically significant effects were observed for the cumulative print plus telephone intervention at 12 months (26% in the intervention vs 18% in the control group) and the print intervention alone at 6 months (15% in the intervention vs 10% in the control group). The effect of the print intervention alone versus the cumulative interventions was not statistically significantly different. Stratified analyses indicated that the intervention was effective among white, Latino, and Asian individuals, but not among African-Americans. CONCLUSIONS: Overall, the intervention was effective in increasing screening rates. Oversampling racial/ethnic minorities allowed for the examination of effects within subgroups, revealing no effect among African American individuals. This finding illustrates the importance of including sufficient numbers of participants from diverse ethnic subgroups in intervention research to enable such stratified analyses. Cancer 2015;121:2951-2959.

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

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

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)

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)