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The theory of mirror matter predicts a hidden sector made up of a copy of the Standard Model particles and interactions but with opposite parity. If mirror matter interacts with ordinary matter, there could be experimentally accessible implications in the form of neutral particle oscillations. Direct searches for neutron oscillations into mirror neutrons in a controlled magnetic field have previously been performed using ultracold neutrons in storage/disappearance measurements, with some inconclusive results consistent with characteristic oscillation time of $tau$$sim$10~s. Here we describe a proposed disappearance and regeneration experiment in which the neutron oscillates to and from a mirror neutron state. An experiment performed using the existing General Purpose-Small Angle Neutron Scattering instrument at the High Flux Isotope Reactor at Oak Ridge National Laboratory could have the sensitivity to exclude up to $tau$$<$15~s in 1 week of beamtime and at low cost.
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Tests on $B-L$ symmetry breaking models are important probes to search for new physics. One proposed model with $Delta(B-L)=2$ involves the oscillations of a neutron to an antineutron. In this paper a new limit on this process is derived for the data acquired from all three operational phases of the Sudbury Neutrino Observatory experiment. The search was concentrated in oscillations occurring within the deuteron, and 23 events are observed against a background expectation of 30.5 events. These translate to a lower limit on the nuclear lifetime of $1.48times 10^{31}$ years at 90% confidence level (CL) when no restriction is placed on the signal likelihood space (unbounded). Alternatively, a lower limit on the nuclear lifetime was found to be $1.18times 10^{31}$ years at 90% CL when the signal was forced into a positive likelihood space (bounded). Values for the free oscillation time derived from various models are also provided in this article. This is the first search for neutron-antineutron oscillation with the deuteron as a target.
We present a detailed report on sterile neutrino oscillation and U-235 antineutrino energy spectrum measurement results from the PROSPECT experiment at the highly enriched High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. In 96 calendar days of data taken at an average baseline distance of 7.9 m from the center of the 85 MW HFIR core, the PROSPECT detector has observed more than 50,000 interactions of antineutrinos produced in beta decays of U-235 fission products. New limits on the oscillation of antineutrinos to light sterile neutrinos have been set by comparing the detected energy spectra of ten reactor-detector baselines between 6.7 and 9.2 meters. Measured differences in energy spectra between baselines show no statistically significant indication of antineutrinos to sterile neutrino oscillation and disfavor the Reactor Antineutrino Anomaly best-fit point at the 2.5$sigma$ confidence level. The reported U-235 antineutrino energy spectrum measurement shows excellent agreement with energy spectrum models generated via conversion of the measured U-235 beta spectrum, with a $chi^2$/DOF of 31/31. PROSPECT is able to disfavor at 2.4$sigma$ confidence level the hypothesis that U-235 antineutrinos are solely responsible for spectrum discrepancies between model and data obtained at commercial reactor cores. A data-model deviation in PROSPECT similar to that observed by commercial core experiments is preferred with respect to no observed deviation, at a 2.2$sigma$ confidence level.
This Letter reports the first measurement of the $^{235}$U $overline{ u_{e}}$ energy spectrum by PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, operating 7.9m from the 85MW$_{mathrm{th}}$ highly-enriched uranium (HEU) High Flux Isotope Reactor. With a surface-based, segmented detector, PROSPECT has observed 31678$pm$304 (stat.) $overline{ u_{e}}$-induced inverse beta decays (IBD), the largest sample from HEU fission to date, 99% of which are attributed to $^{235}$U. Despite broad agreement, comparison of the Huber $^{235}$U model to the measured spectrum produces a $chi^2/ndf = 51.4/31$, driven primarily by deviations in two localized energy regions. The measured $^{235}$U spectrum shape is consistent with a deviation relative to prediction equal in size to that observed at low-enriched uranium power reactors in the $overline{ u_{e}}$ energy region of 5-7MeV.
The Majorana Demonstrator is an ultra low-background experiment searching for neutrinoless double-beta decay in $^{76}$Ge. The heavily shielded array of germanium detectors, placed nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota, also allows searches for new exotic physics. We present the first limits for tri-nucleon decay-specific modes and invisible decay modes for Ge isotopes. We find a half-life limit of $4.9 times 10^{25}$ yr for the decay $^{76}{rm Ge(ppn)} to {}^{73}{rm Zn} e^+pi^+$ and $4.7times10^{25}$ yr for the decay $^{76}{rm Ge(ppp)} to ^{73}{rm Cu} e^+pi^+pi^+$. The half-life limit for the invisible tri-proton decay mode of $^{76}$Ge was found to be $7.5times10^{24}$ yr.
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$ GW$_{rm th}$-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 two 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 $sin^{2}2theta_{13}$ and $|Delta m^2_{ee}|$ were halved as a result of these improvements. Analysis of the relative antineutrino rates and energy spectra between detectors gave $sin^{2}2theta_{13} = 0.084pm0.005$ and $|Delta m^{2}_{ee}|= (2.42pm0.11) times 10^{-3}$ eV$^2$ in the three-neutrino framework.
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