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Register a new userSearch for short baseline $ u_e$ disappearance with the T2K near detector
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The T2K experiment has performed a search for $ u_e$ disappearance due to sterile neutrinos using $5.9 times 10^{20}$ protons on target for a baseline of $280 m$ in a neutrino beam peaked at about $500 MeV$. A sample of u_e CC interactions in the off-axis near detector has been selected with a purity of 63% and an efficiency of 26%. The p-value for the null hypothesis is 0.085 and the excluded region at 95% CL is approximately $sin^2 2 theta_{ee} > 0.3$ for $Delta m^2_{eff} > 7 eV^2 / c^4$.
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This paper reports on the search for heavy neutrinos with masses in the range $140 < M_N < 493$ MeV/c$^2$ using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are $N to ell^{pm}_{alpha} pi^{mp}$ and $N to ell^+_{alpha} ell^-_{beta} u (bar u)$ ($alpha,beta=e,mu$). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavoured currents ($U_e^2$, $U_{mu}^2$, $U_{tau}^2$) as a function of the heavy neutrino mass, e.g. $U_e^2 < 10^{-9}$ at $90%$ C.L. for a mass of $390$ MeV/c$^2$. These constraints are competitive with previous experiments.
We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7 (7.6)$times 10^{20}$ protons on target in neutrino (antineutrino) mode. A selection of neutral current interaction samples are also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude $sin^2theta_{24}$ for the sterile neutrino mass splitting $Delta m^2_{41}<3times 10^{-3}$ eV$^2/c^4$.
Reactor antineutrino experiments have the ability to search for neutrino oscillations independent of reactor flux predictions using a relative measurement of the neutrino flux and spectrum across a range of baselines. The range of accessible oscillation parameters are determined by the baselines of the detector arrangement. We examine the sensitivity of short-baseline experiments with more than one detector and discuss the optimization of a second, far detector. The extended reach in baselines of a 2-detector experiment will improve sensitivity to short-baseline neutrino oscillations while also increasing the ability to distinguish between 3+1 mixing and other non-standard models.
Neutrino neutral-current induced single photon production is a sub-leading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the fine-grained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron-positron pairs, we achieved 95% pure gamma ray sample from 5.738$times 10^{20}$ protons-on-targets neutrino mode data. We do not find positive evidence of neutral current induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at 0.114$times 10^{-38}$ cm$^2$ (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of $left<E_ uright>sim 0.6$ GeV. This is the first limit on this process below 1 GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.
This Letter reports the first scientific results from the observation of antineutrinos emitted by fission products of $^{235}$U at the High Flux Isotope Reactor. PROSPECT, the Precision Reactor Oscillation and Spectrum Experiment, consists of a segmented 4 ton $^6$Li-doped liquid scintillator detector covering a baseline range of 7-9 m from the reactor and operating under less than 1 meter water equivalent overburden. Data collected during 33 live-days of reactor operation at a nominal power of 85 MW yields a detection of 25461 $pm$ 283 (stat.) inverse beta decays. Observation of reactor antineutrinos can be achieved in PROSPECT at 5$sigma$ statistical significance within two hours of on-surface reactor-on data-taking. A reactor-model independent analysis of the inverse beta decay prompt energy spectrum as a function of baseline constrains significant portions of the previously allowed sterile neutrino oscillation parameter space at 95% confidence level and disfavors the best fit of the Reactor Antineutrino Anomaly at 2.2$sigma$ confidence level.
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