Measurement of Muon Antineutrino Oscillations with an Accelerator-Produced Off-Axis Beam

TL;DR

This paper reports the first measurement of muon antineutrino oscillation parameters using an off-axis accelerator beam, confirming consistency with previous neutrino and antineutrino oscillation results.

Contribution

It presents the first measurement of muon antineutrino disappearance parameters with an off-axis beam at T2K, providing new experimental data on antineutrino oscillations.

Findings

Measured oscillation parameters: sin^2(θ23) = 0.45, |Δm^2_32| = 2.51×10^{-3} eV^2

Observed 34 muon-like events with dataset of 4.01×10^{20} protons on target

Results agree with previous neutrino and antineutrino oscillation measurements.

Abstract

T2K reports its first measurements of the parameters governing the disappearance of $\bar{\nu}_\mu$ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic $\bar{\nu}_\mu$ 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 $\bar{\nu}_\mu$ 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 $|\Delta\bar{m}^2_{32}| = 2.51 \times 10^{-3}$ 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 $\nu_\mu$ disappearance parameters measured by T2K.