Oscillation Research with Cosmics in the Abyss

The aim of ORCA (Oscillation Research with Cosmics in the Abyss) is to measure the Neutrino Mass Hierarchy using the oscillations of atmospheric neutrinos through the Earth in the GeV range, with a dense neutrino telescope. This particular energy range is also suitable for other studies (dark matter indirect detection for instance).

The recent measurement of a large θ13 mixing angle in reactor and accelerator experiments opens the possibility of a measurement of the neutrino mass hierarchy (MH) by studying the influence of matter effects on the energy distribution and the zenith angular distribution of atmospheric neutrinos.

"Normal" and "inverted" neutrino mass hierarchy.

The goal of the KM3NeT Collaboration is to construct a multi-km3 deep sea neutrino telescope in the Mediterranean Sea. KM3NeT/ARCA, optimised for the discovery of cosmic neutrinos from astrophysical sources in the TeV-PeV range, will be located on the italian site, near Sicily. KM3NeT/ORCA, optimised for the measurement of the Neutrino Mass Hierarchy with GeV neutrinos, will be located offshore Toulon, not far from the ANTARES site. Such an optimisation leads to a denser distribution of photosensors and a correspondingly reduced instrumented volume. Such geometry would also provide excellent performance for neutrinos from dark matter annihilation in the Sun and Galactic centre. 

A possible configuration for the KM3NeT neutrino telescope - ORCA, its possible first phase optimized for 1-20 GeV neutrinos, would consist in 115 of these lines, with closer storeys (9m) and a denser line spacing (20m).

Simulations have shown that the foreseen geometry would allow to reach a significance of 3σ in the determination of the Neutrino Mass Hierarchy, after 3 years of operation, as shown on the plot below, extracted from the Letter of Intent of KM3NeT 2.0.