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Register a new userMeasurement of Neutrino Oscillation Parameters from Muon Neutrino Disappearance with an Off-axis Beam
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The T2K collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Super-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to $3.01 times 10^{20}$ protons on target. In the absence of neutrino oscillations, $205 pm 17$ (syst.) events are expected to be detected and only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum assuming three neutrino flavors, normal mass hierarchy and $theta_{23}leq pi/4$ yields a best-fit mixing angle $sin^2(2theta_{23})=1.000$ and mass splitting $|Delta m^2_{32}| =2.44 times 10^{-3}$ eV$^2$/c$^4$. If $theta_{23}geq pi/4$ is assumed, the best-fit mixing angle changes to $sin^2(2theta_{23})=0.999$ and the mass splitting remains unchanged.
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We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43 10**20 protons on target, we observe 31 fully-contained single muon-like ring events in Super-Kamiokande, compared with an expectation of 104 +- 14 (syst) events without neutrino oscillations. The best-fit point for two-flavor nu_mu -> nu_tau oscillations is sin**2(2 theta_23) = 0.98 and |Delta m**2_32| = 2.65 10**-3 eV**2. The boundary of the 90 % confidence region includes the points (sin**2(2 theta_23),|Delta m**2_32|) = (1.0, 3.1 10**-3 eV**2), (0.84, 2.65 10**-3 eV**2) and (1.0, 2.2 10**-3 eV**2).
New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter theta_{23}. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57 x 10^{20} protons on target, T2K has fit the energy-dependent nu_mu oscillation probability to determine oscillation parameters. Marginalizing over the values of other oscillation parameters yields sin^2 (theta_{23}) = 0.514 +0.055/-0.056 (0.511 +- 0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Delta m^2_{32} = (2.51 +- 0.10) x 10^{-3} eV^2/c^4 (inverted hierarchy: Delta m^2_{13} = (2.48 +- 0.10) x 10^{-3} eV^2/c^4). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.
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.
We present a measurement of neutrino oscillations via atmospheric muon neutrino disappearance with three years of data of the completed IceCube neutrino detector. DeepCore, a region of denser instrumentation, enables the detection and reconstruction of atmospheric muon neutrinos between 10 GeV and 100 GeV, where a strong disappearance signal is expected. The detector volume surrounding DeepCore is used as a veto region to suppress the atmospheric muon background. Neutrino events are selected where the detected Cherenkov photons of the secondary particles minimally scatter, and the neutrino energy and arrival direction are reconstructed. Both variables are used to obtain the neutrino oscillation parameters from the data, with the best fit given by $Delta m^2_{32}=2.72^{+0.19}_{-0.20}times 10^{-3},mathrm{eV}^2$ and $sin^2theta_{23} = 0.53^{+0.09}_{-0.12}$ (normal mass hierarchy assumed). The results are compatible and comparable in precision to those of dedicated oscillation experiments.
T2K reports its first measurements of the parameters governing the disappearance of $bar{ u}_mu$ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic $bar{ u}_mu$ beam, produced with a peak energy of 0.6 GeV at J-PARC, is observed at the far detector Super-Kamiokande, 295 km away, where the $bar{ u}_mu$ survival probability is expected to be minimal. Using a dataset corresponding to $4.01 times 10^{20}$ protons on target, $34$ fully contained $mu$-like events were observed. The best-fit oscillation parameters are $sin^2 (bar{theta}_{23}) = 0.45$ and $|Deltabar{m}^2_{32}| = 2.51 times 10^{-3}$ eV$^2$ with 68% confidence intervals of 0.38 - 0.64 and 2.26 - 2.80 $times 10^{-3}$ eV$^2$ respectively. These results are in agreement with existing antineutrino parameter measurements and also with the $ u_mu$ disappearance parameters measured by T2K.
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