Determining the Neutrino Mass Ordering and Oscillation Parameters with KM3NeT/ORCA

TL;DR

This paper evaluates KM3NeT/ORCA's ability to determine neutrino mass ordering and oscillation parameters using atmospheric neutrinos, achieving significant sensitivity and precision after three years of data collection.

Contribution

The study provides the first detailed sensitivity analysis of KM3NeT/ORCA for neutrino mass ordering and oscillation parameters, including a unitarity test of the leptonic mixing matrix.

Findings

Neutrino mass ordering can be determined with 4.4σ (normal) and 2.3σ (inverted) significance after three years.

Estimated precision for Δm²₃₂ is 85×10⁻⁶ eV² (normal) and 75×10⁻⁶ eV² (inverted).

Tau neutrino rate variations larger than 20% can be excluded at 3σ.

Abstract

The next generation of water Cherenkov neutrino telescopes in the Mediterranean Sea are under construction offshore France (KM3NeT/ORCA) and Sicily (KM3NeT/ARCA). The KM3NeT/ORCA detector features an energy detection threshold which allows to collect atmospheric neutrinos to study flavour oscillation. This paper reports the KM3NeT/ORCA sensitivity to this phenomenon. The event reconstruction, selection and classification are described. The sensitivity to determine the neutrino mass ordering was evaluated and found to be 4.4 $\sigma$ if the true ordering is normal and 2.3 $\sigma$ if inverted, after three years of data taking. The precision to measure $\Delta m^2_{32}$ and $\theta_{23}$ were also estimated and found to be $85\cdot10^{-6}$ eV$^2$ and $(^{+1.9}_{-3.1})^{\circ}$ for normal neutrino mass ordering and, $75\cdot10^{-6}$ eV$^2$ and $(^{+2.0}_{-7.0})^{\circ}$ for inverted ordering. Finally, a unitarity test of the leptonic mixing matrix by measuring the rate of tau neutrinos is described. Three years of data taking were found to be sufficient to exclude $\nu_{\tau}$ and $\bar{\nu}_{\tau}$ event rate variations larger than 20% at $3\sigma$ level.