First direct observation of muon antineutrino disappearance

TL;DR

This paper reports the first direct detection of muon antineutrino disappearance, providing evidence for neutrino oscillations and measuring their oscillation parameters with high significance.

Contribution

It presents the first direct observation of muon antineutrino disappearance and precise measurement of their oscillation parameters using the MINOS experiment.

Findings

Disappearance of muon antineutrinos observed with 6.3σ significance.

Measured oscillation parameters: Δm² ≈ 3.36×10⁻³ eV², sin²(2θ) ≈ 0.86.

Muon neutrino and antineutrino oscillation measurements are consistent at 2.0% confidence level.

Abstract

This letter reports the first direct observation of muon antineutrino disappearance. The MINOS experiment has taken data with an accelerator beam optimized for muon antineutrino production, accumulating an exposure of $1.71\times 10^{20}$ protons on target. In the Far Detector, 97 charged current muon antineutrino events are observed. The no-oscillation hypothesis predicts 156 events and is excluded at $6.3\sigma$. The best fit to oscillation yields $\Delta \bar{m}^{2}=(3.36^{+0.46}_{-0.40}\textrm{(stat.)}\pm0.06\textrm{(syst.)})\times 10^{-3}\,\eV^{2}$, $\sin^{2}(2\bar{\theta})=0.86^{+0.11}_{-0.12}\textrm{(stat.)}\pm0.01\textrm{(syst.)}$. The MINOS muon neutrino and muon antineutrino measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters.