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Register a new userMeasurement of neutrino oscillations by means of a high density detector on the atmospheric neutrino beam
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A high-density calorimeter, consisting of magnetized iron planes interleaved by RPCs, as tracking and timing devices, is a good candidate for a next generation experiment on atmospheric neutrinos. With 34 kt of mass and in four years of data taking, this experiment will be sensitive to $ u_mu to u_x$ oscillation with $Delta m^2 > 6 times 10^{-5}$ and mixing near to maximal and fully cover the region of oscillation parameters suggested by Super-Kamiokande results. Moreover, the experimental method will enable to measure the oscillation parameters from the modulation of the L/E spectrum ($ u_mu$ disappearance). For $Delta m^2 > 3 times 10^{-3}$ eV$^2$, this experiment can also establish whether the oscillation occurs into a tau or a sterile neutrino, by looking for an excess of muon-less events at high energies produced by upward-going tau neutrinos ($ u_tau$ appearance).
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The data taken with the ANTARES neutrino telescope from 2007 to 2010, a total live time of 863 days, are used to measure the oscillation parameters of atmospheric neutrinos. Muon tracks are reconstructed with energies as low as 20 GeV. Neutrino oscillations will cause a suppression of vertical upgoing muon neutrinos of such energies crossing the Earth. The parameters determining the oscillation of atmospheric neutrinos are extracted by fitting the event rate as a function of the ratio of the estimated neutrino energy and reconstructed flight path through the Earth. Measurement contours of the oscillation parameters in a two-flavour approximation are derived. Assuming maximum mixing, a mass difference of $Delta m_{32}^2=(3.1pm 0.9)cdot 10^{-3}$ eV$^2$ is obtained, in good agreement with the world average value.
Two independent methods are employed to measure the neutrino flux of the anti-neutrino-mode beam observed by the MiniBooNE detector. The first method compares data to simulated event rates in a high purity $ umu$ induced charged-current single $pip$ (CC1$pip$) sample while the second exploits the difference between the angular distributions of muons created in $ umu$ and $ umub$ charged-current quasi-elastic (CCQE) interactions. The results from both analyses indicate the prediction of the neutrino flux component of the pre-dominately anti-neutrino beam is over-estimated - the CC1$pip$ analysis indicates the predicted $ umu$ flux should be scaled by $0.76 pm 0.11$, while the CCQE angular fit yields $0.65 pm 0.23$. The energy spectrum of the flux prediction is checked by repeating the analyses in bins of reconstructed neutrino energy, and the results show that the spectral shape is well modeled. These analyses are a demonstration of techniques for measuring the neutrino contamination of anti-neutrino beams observed by future non-magnetized detectors.
Neutrino oscillations have been probed during the last few decades using multiple neutrino sources and experimental set-ups. In the recent years, very large volume neutrino telescopes have started contributing to the field. First ANTARES and then IceCube have relied on large and sparsely instrumented volumes to observe atmospheric neutrinos for combinations of baselines and energies inaccessible to other experiments. Using this advantage, the latest result from IceCube starts approaching the precision of other established technologies, and is paving the way for future detectors, such as ORCA and PINGU. These new projects seek to provide better measurements of neutrino oscillation parameters, and eventually determine the neutrino mass ordering. The results from running experiments and the potential from proposed projects are discussed in this review, emphasizing the experimental challenges involved in the measurements.
We report measurements of oscillation parameters from $ u_{mu}$ and $bar{ u}_{mu}$ disappearance using beam and atmospheric data from MINOS. The data comprise exposures of unit[$10.71 times 10^{20}$]{protons on target (POT)} in the $ u_{mu}$-dominated beam, $unit[3.36times10^{20}]{POT}}$ in the $bar{ u}_{mu}$-enhanced beam, and 37.88 kton-years of atmospheric neutrinos. Assuming identical $ u$ and $bar{ u}$ oscillation parameters, we measure mbox{$|Delta m^2}| = unit[2.41^{+0.09}_{-0.10}) times 10^{-3}]{eV^{2}}$} and $sin^{2}/!/left(2theta right) = 0.950^{+0.035}_{-0.036}$. Allowing independent $ u$ and $bar{ u}$ oscillations, we measure antineutrino parameters of $|Delta bar{m}^2| = unit[(2.50 ^{+0.23}_{-0.25}) times 10^{-3}]{eV^{2}}$ and $sin^{2}/!/left(2bar{theta} right) = 0.97^{+0.03}_{-0.08}$, with minimal change to the neutrino parameters.
Using 5,326 days of atmospheric neutrino data, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment. Super-Kamiokande measures the tau normalization to be 1.47$pm$0.32 under the assumption of normal neutrino hierarchy, relative to the expectation of unity with neutrino oscillation. The result excludes the hypothesis of no-tau-appearance with a significance level of 4.6$sigma$. The inclusive charged-current tau neutrino cross section averaged by the tau neutrino flux at Super-Kamiokande is measured to be $(0.94pm0.20)times 10^{-38}$ cm$^{2}$. The measurement is consistent with the Standard Model prediction, agreeing to within 1.5$sigma$.
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