KM3NeT is a large Research Infrastructure that will consist of a network of deep-sea neutrino telescopes in the Mediterranean Sea. It will combine the study of fundamental particle physics with observation of the sources of high-energy cosmic neutrinos, yielding a unique way to study the Universe.
The infrastructure consists of three so-called building blocks. A building block is comprised of 115 strings, each string has 18 optical modules module with 31 photo-multiplier tubes (PMTs). This 3-dimensional array of photo-sensors allows for the detection of the Cherenkov light produced by relativistic particles emerging from neutrino interactions. Two building blocks will be configured to fully explore cosmic neutrino sources (ARCA: Astroparticle Research with Cosmics in the Abyss). One building block will be configured to measure precisely atmospheric neutrino oscillations (ORCA: Oscillations Research with Cosmics in the Abyss). ARCA will be realised at the Capo Passero site (Italy) and ORCA at the Toulon site (France). The technical implementation of ARCA and ORCA is almost identical. The deep-sea sites are linked to shore with a network of cables for electrical power and high-bandwidth fibre-optic communication. On site, shore stations provide power, computing and high-bandwidth connections to central data repositories. The flexible and cost-effective detector design has major Dutch intellectual and technical contributions.
The collaboration has opted for a phased implementation of KM3NET. Phase-1 includes a validation programme, partial construction of the sea-floor networks and the installation of 31 strings. Currently 5 strings are deployed and operational (4 ORCA, 1 ARCA), 2 more ORCA strings are ready to be deployed. 90% of the optical modules to complete phase-1 have been built and integration into strings is in progress. Data taking with the deployed strings has started and first commissioning results are obtained. The data includes recorded optical data (precisely-timed hits in the PMTs), acoustic data and environmental data such as water temperature and current. Apart from calibration periods, data taking proceeds on a 24/7 basis. All data is sent to the shore stations, where it is filtered for interesting events.
While phase-1 is being completed, the procurement of components for the first strings of phase-2 (i.e. KM3NeT 2.0, the full three building blocks of 115 strings each) is progressing in parallel. The recent proof that the neutrino mixing angle theta_13 is large, and the evidence by IceCube (South Pole) that high-energy cosmic neutrinos exist, enhances the scientific program and strongly motivates the full completion of KM3NeT 2.0. With this upgrade, a research infrastructure will be realised ideally suited for the discovery and subsequent observation of the sources of high-energy neutrinos in the Universe and for determining the mass hierarchy of neutrinos. KM3NeT also offers interdisciplinary opportunities for continuous, real-time measurements, e.g. for marine biology, oceanography or environmental sciences.
The Collaboration will complete the construction of ORCA and ARCA by 2024 c.q. 2026, assuming that funding for completion is available.