Abstract
T2K reports its first measurements of the parameters governing the disappearance of ν[over ¯]_{μ} in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic ν[over ¯]_{μ} beam, produced with a peak energy of 0.6GeV at J-PARC, is observed at the far detector Super-Kamiokande, 295km away, where the ν[over ¯]_{μ} survival probability is expected to be minimal. Using a data set corresponding to 4.01×10^{20} protons on target, 34 fully contained μ-like events were observed. The best-fit oscillation parameters are sin^{2}(θ[over ¯]_{23})=0.45 and |Δm[over ¯]_{32}^{2}|=2.51×10^{-3} eV^{2} with 68%confidence intervals of 0.38-0.64 and 2.26-2.80×10^{-3} eV^{2}, respectively. These results are in agreement with existing antineutrino parameter measurements and also with the ν_{μ} disappearance parameters measured by T2K.
Highlights
T2K reports its first measurements of the parameters governing the disappearance of νμ in an off-axis beam
flavor change induced by neutrino oscillations
Using a data set corresponding to 4.01 × 1020 protons on target
Summary
Θ13, θ12, and Δm 221 are assumed to be identical to their matter counterparts since our data set cannot constrain them This ensures that the expected background at the far detector is consistent with the current knowledge of neutrino oscillations, while allowing us to use the T2K antineutrino-mode data to measure θ23 and Δm 232. [13], fitting samples of charged-current (CC) interactions at ND280 to produce a tuned prediction of the unoscillated antineutrino spectrum at the far detector, including its associated uncertainty [13] in that both νμ and νμ samples at ND280 are fitted This ensures that the neutrino interaction model is consistent between both neutrino- and antineutrino-beammode data sets and provides a constraint on both the right-sign signal and the wrong-sign background in the antineutrino-mode beam. Sample νμ CC 0π νμ CC 1πþ νμ CC other νμ CC 1 track νμ CC N tracks νμ CC 1 track νμ CC N tracks
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