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Register a new userEvidence for Neutrino Oscillations from the Observation of Electron Anti-neutrinos in a Muon Anti-Neutrino Beam
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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.
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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 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.).
The magnetised Iron Calorimeter detector at the India-based Neutrino Observatory (INO) has a unique feature to identify the neutrinos and antineutrinos on an event by event basis. This feature can be harnessed to detect the differences between the oscillation parameters of neutrinos and antineutrinos independently. In this paper, we analysed Charged Current $ u_{mu}$ and $overline{ u}_{mu}$ events under the influence of earth matter effect using three neutrino flavor oscillation framework. If the atmospheric mass-squared differences and mixing parameters for neutrinos are different from antineutrinos, we present the prospects for the experimental observation of these differences in atmospheric $ u$ and $overline u_{mu}$ oscillations at INO. We estimate the detector sensitivity to confirm a non-zero difference in the mass-squared splittings ($|Delta m^{2}_{32}|-|Deltaoverline{m^{2}}_{32}|$) for neutrinos and antineutrinos.
We report the results of a search for $ u_{e}$ appearance in a $ u_{mu}$ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of $8.2times10^{20}$ protons on the NuMI target at Fermilab, we find that $2sin^2(theta_{23})sin^2(2theta_{13})<0.12 (0.20)$ at 90% confidence level for $deltamathord{=}0$ and the normal (inverted) neutrino mass hierarchy, with a best fit of $2sin^2(theta_{23})sin^2(2theta_{13}),mathord{=},0.041^{+0.047}_{-0.031} (0.079^{+0.071}_{-0.053})$. The $theta_{13}mathord{=}0$ hypothesis is disfavored by the MINOS data at the 89% confidence level.
Neutrinos propagating through matter may participate in forward coherent neutral-current-like scattering arising from non-standard interactions as well as from the Mikheyev-Smirnov-Wolfenstein matter potential $V_e$. We show that at fixed long baselines through matter of constant density, the non-standard interaction potential $epsilon_{mutau} V_e$ can contribute an additional term to the oscillation phase whose sign differs for $anumu$ versus $ umu$ propagation in matter. Its presence can cause different apparent $Delta m^2$ to be erroneously inferred on the basis of oscillations in vacuum, with values lying above (for $anumu$) or below (for $ umu$) the actual $Delta m^2_{32}$ for the case where $epsilon_{mutau}$ is predominantly real-valued and of sign opposite to $Delta m_{32}^2$. An NSI scenario invoking only $Re(epsilon_{mutau})$ is shown to be capable of accounting for a disparity recently reported between oscillation survival for $anumu$ and $ umu$ fluxes measured at $735~mathrm{km}$ by the MINOS experiment. Implications for mantle traversal by atmospheric neutrinos are examined. The NSI matter potential with non-maximal mixing could evade conventional atmospheric neutrino analyses which do not distinguish $ umu$ from $anumu$ on an event-by-event basis.
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