Measurement of Neutrino Oscillation Parameters from Muon Neutrino Disappearance with an Off-axis Beam

TL;DR

This paper presents a precise measurement of muon neutrino disappearance using an off-axis beam, constraining neutrino oscillation parameters with data from the T2K experiment and Super-Kamiokande detector.

Contribution

The study provides the most precise measurement of the mixing angle and mass splitting for muon neutrino oscillations using an off-axis beam and near detector constraints.

Findings

Best-fit mixing angle $ heta_{23}$ close to maximal mixing.

Mass splitting $| riangle m^2_{32}|$ measured at $2.44 imes 10^{-3}$ eV$^2$/c$^4$.

Significant deficit of muon neutrinos observed, confirming oscillation.

Abstract

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 $\sin^2(2\theta_{23})=1.000$ 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 $\sin^2(2\theta_{23})=0.999$ and the mass splitting remains unchanged.