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Register a new userEvidence of Electron Neutrino Appearance in a Muon Neutrino Beam
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The T2K collaboration: reports evidence for electron neutrino appearance at the atmospheric mass splitting, |Delta m_{32}^2|=2.4x10^{-3} eV^2. An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beams origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of 3.3pm0.4(syst.) events is expected. The background-only hypothesis is rejected with a p-value of 0.0009 (3.1sigma), and a fit assuming u_{mu}-> u_e oscillations with sin^2(2theta_{23})=1, delta_{CP}=0 and |Delta m_{32}^2|=2.4x10^{-3} eV^2 yields sin^2(2theta_{13})=0.088^{+0.049}_{-0.039}(stat.+syst.).
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The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of 7.3$sigma$ when compared to 4.92 $pm$ 0.55 expected background events. In the PMNS mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles $theta_{12}$, $theta_{23}$, $theta_{13}$, a mass difference $Delta m^2_{32}$ and a CP violating phase $delta_{mathrm{CP}}$. In this neutrino oscillation scenario, assuming $|Delta m^2_{32}| = 2.4 times 10^{-3}$ $rm eV^2$, $sin^2 theta_{23} = 0.5$, and $Delta m^2_{32} >0$ ($Delta m^2_{32} <0$), a best-fit value of $sin^2 2 theta_{13}$ = $0.140^{+0.038}_{-0.032}$ ($0.170^{+0.045}_{-0.037}$) is obtained at $delta_{mathrm{CP}}=0$. When combining the result with the current best knowledge of oscillation parameters including the world average value of $theta_{13}$ from reactor experiments, some values of $delta_{mathrm{CP}}$ are disfavored at the 90% CL.
The T2K experiment observes indications of $ u_murightarrow u_e$ appearance in data accumulated with $1.43times10^{20}$ protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with $|Delta m_{23}^2|=2.4times10^{-3}$ eV$^2$, $sin^2 2theta_{23}=1$ and $sin^2 2theta_{13}=0$, the expected number of such events is 1.5$pm$0.3(syst.). Under this hypothesis, the probability to observe six or more candidate events is 7$times10^{-3}$, equivalent to 2.5$sigma$ significance. At 90% C.L., the data are consistent with 0.03(0.04)$<sin^2 2theta_{13}<$ 0.28(0.34) for $delta_{rm CP}=0$ and a normal (inverted) hierarchy.
A search for muon anti-neutrino to electron anti-neutrino oscillations was conducted by the Liquid Scintillator Neutrino Detector at the Los Alamos Neutron Science Center using muon anti-neutrinos from positive muon decay at rest. A total excess of 87.9 +/- 22.4 +/- 6.0 events consistent with electron anti-neutrino plus proton scattering to positron plus neutron was observed above the expected background. This excess corresponds to an oscillation probability of (0.264 +/- 0.067 +/- 0.045), which is consistent with an earlier analysis. In conjunction with other known limits on neutrino oscillations, the LSND data suggest that neutrino oscillations occur in the 0.2-10 eV^2/c^4 Delta-m^2 range, indicating a neutrino mass greater than 0.4 eV/c^2.
We report results from the first search for $ u_muto u_e$ transitions by the NOvA experiment. In an exposure equivalent to $2.74times10^{20}$ protons-on-target in the upgraded NuMI beam at Fermilab, we observe 6 events in the Far Detector, compared to a background expectation of $0.99pm0.11$ (syst.) events based on the Near Detector measurement. A secondary analysis observes 11 events with a background of $1.07pm0.14$ (syst.). The $3.3sigma$ excess of events observed in the primary analysis disfavors $0.1pi < delta_{CP} < 0.5pi$ in the inverted mass hierarchy at the 90% C.L.
The OPERA experiment was designed to search for $ u_{mu} rightarrow u_{tau}$ oscillations in appearance mode, i.e. by detecting the $tau$-leptons produced in charged current $ u_{tau}$ interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of $ u_{mu} rightarrow u_{tau}$ appearance, achieved with four candidate events in a sub-sample of the data, was previously reported. In this paper, a fifth $ u_{tau}$ candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow assessing the discovery of $ u_{mu}rightarrow u_{tau}$ oscillations in appearance mode with a significance larger than 5 $sigma$.
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