Measuring the neutrino mass hierarchy with KM3NeT/ORCA

ORCA is the low-energy branch of KM3NeT, the next-generation research infrastructure hosting underwater Cherenkov detectors in the Mediterranean Sea. ORCA's primary goal is the determination of the neutrino mass hierarchy by measuring the matter- induced modifications on the oscillation probabilities of few-GeV atmospheric neutrinos. The technical design of the ORCA detector foresees a dense configuration of optical modules, optimised for the study of interactions of neutrinos in the energy range of 3–30 GeV. The first ORCA detection string was successfully deployed on 22nd September 2017 and is providing high-quality data since then. With an instrumented mass of 8 Mton for the full-size ORCA detector, it will be possible to probe with a high-statistics neutrino sample a wide range of energies and baselines through the Earth. This allows to detmerine the neutrino mass hierarchy with 3 σ after 3–4 years of operation, to probe the unitarity assumption of 3-neutrino mixing with a high-statistics measurement of tau-neutrino appearance in the atmospheric neutrino flux, and to improve the measurement precision on other oscillation parameters.