First Muon-Neutrino Disappearance Study with an Off-Axis Beam

TL;DR

This paper reports the first muon-neutrino disappearance measurement using an off-axis beam in a long-baseline experiment, providing key insights into neutrino oscillation parameters with significant statistical evidence.

Contribution

It introduces the first use of the off-axis technique in a long-baseline neutrino experiment and measures neutrino oscillation parameters with new experimental data.

Findings

Observed 31 muon-like events versus 104 expected without oscillations.

Best-fit oscillation parameters are sin^2(2θ_23)=0.98 and |Δm^2_32|=2.65×10^-3 eV^2.

Established confidence regions for neutrino oscillation parameters.

Abstract

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).