  ORCA (Oscillation Research with Cosmics in the Abyss) 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 ORCA detector design foresees a dense configuration
of KM3NeT neutrino detection technology, optimised for measuring the
interactions of neutrinos in the energy range of 3 - 20 GeV. To be deployed at
the French KM3NeT site, ORCA's multi-PMT optical modules will exploit the
excellent optical properties of deep-sea water to accurately reconstruct both
shower-like (mostly electron neutrino) and track-like (mostly muon neutrino)
events in order to collect a high-statistics sample of few-GeV neutrino events.
This contribution reviews the methods and technology of the ORCA detector, and
discusses the prospects for measuring the neutrino mass hierarchy as well as
the potential to improve the measurement precision on other oscillation
parameters.
