KM3NeT is a large research infrastructure, under construction in the Mediterranean Sea, distributed over two sites: the first one in Italy, 80 km south east of Capo Passero at a depth of 3500 m, and the second one in France, 40 km South of Toulon at a depth of 2500 m. The infrastructure will host two neutrino detectors and instrumentation for research in the field of marine science and geology. Both sites have a seafloor network of electro-optical cables for electrical power distribution and broadband transmission of the telescope data. A main electro-optical cable is connected to a shore laboratory.
The neutrino telescope of the Italian site (ARCA, Astroparticle Research with Cosmics in the Abyss) will be dedicated to the high energy neutrino astronomy, while the detector of the French site (ORCA, Oscillation Research with Cosmics in the Abyss) will be dedicated to the study of neutrino fundamental properties. The detectors consist of detection units, vertical structures equipped with optical sensors that detect the Cherenkov light generated by secondary particles produced in the neutrino interactions with water. Both detectors consist of the same elements but with a different granularity of optical sensors. The ARCA detector, which will consist of 230 detection units, organized in two “building blocks", with a total of more than 4000 optical sensors, will have a total volume of about 1 km3.
Fig. 1: Artistic view of a sea campaign with deployment of multiple detection units. (Copyright Marijn van der Meer/Quest).
Astronomy with neutrinos is the new frontier in astrophysical research. ARCA, with a volume of about 1 km3, will be able to study neutrinos from astrophysical sources such as supernovae, gamma ray bursts or active galactic nuclei. Thanks to its location in the northern hemisphere, KM3NeT will provide a sky coverage complementary to that of IceCube, a similar telescope for neutrinos operating at the South Pole. KM3NeT will observe, in particular, the region of the galactic plane with an unprecedented angular resolution.
The KM3NeT collaboration comprises more than 250 researchers, mainly European, who have been involved in the design and now in the construction of the two detectors and of the seafloor infrastructure. INFN is involved with ten branches and labs. The LNS are the reference laboratory for the KM3NeT-ARCA node. They operate the shore station, located in Portopalo di Capo Passero (SR), where the power system, the data acquisition system and the control system are housed. This station is connected to the LNS headquarters in Catania by means of a high-speed fibre optic link, which allows for the remote control and operation of the equipment.
Fig. 2: Optical module supported by two parallel ropes.
The LNS are also at the forefront in the construction of the apparatus with an integration site for the detection units and in the construction of the seafloor network. Data from the first detection units already installed proved the validity of the design. The seafloor network is currently being expanded and the collaboration is in the construction phase of the detection units. ARCA will be the first large apparatus ever built in an unknown and hostile environment such as the great sea depths.