KM3NeT

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Artist's impression of the KM3NeT neutrino telescope anchored to the seabed.
KM3NeT logo

KM3NeT, an acronym for Cubic Kilometre Neutrino Telescope, is a future European research infrastructure that will be located at the bottom of the Mediterranean Sea. It will host the next-generation neutrino telescope in the form of a water Cherenkov detector with an instrumented volume of about five cubic kilometres distributed over three locations in the Mediterranean: KM3NeT-Fr (off-shore Toulon, France), KM3NeT-It (off-shore Portopalo di Capo Passero, Sicily, Italy) and KM3NeT-Gr (off-shore Pylos, Peloponnese, Greece).

KM3NeT will search for neutrinos from distant astrophysical sources like supernova remnants, gamma-ray bursts, supernovae or colliding stars and will be a powerful tool in the search for dark matter in the universe. Its prime objective is to detect neutrinos from sources in our galaxy. Arrays of thousands of optical sensor modules will detect the faint light in the deep sea from charged particles originating from collisions of the neutrinos and the water or rock in the vicinity of the detector. The research infrastructure will also house instrumentation for other sciences like marine biology, oceanography and geophysics for long-term and on-line monitoring of the deep-sea environment and the sea bottom at depth of several kilometres.

Once completed, the KM3NeT research infrastructure will consists of seven large subdetectors. Six of these will indeed form the telescope searching neutrino-sources. The seventh subdetector will be optimised to measure the properties of the neutrino itself. In that sense, the latter detector is a neutrino particle physics detector.

Design[edit]

KM3NeT Digital Optical Module (DOM) in the laboratory

The full neutrino telescope will contain on the order of 12000 pressure-resistant glass spheres attached to about 600 strings. The strings hold 18 sensor spheres each, anchored to the sea floor and supported by floats. Each sphere, called a "digital optical module" (DOM), is about 17 inches (43 cm) in diameter, contains 31 3-inch (7.6 cm) photomultiplier tubes with supporting electronics, and is connected to shore via a high-bandwidth optical network.

At the shore of each KM3NeT installation site, a farm of computers will perform the first data filter in the search for the signal of cosmic neutrinos, prior to streaming the data to a central KM3NeT data centre for storage and further analysis by the KM3NeT scientists.

The KM3NeT-It site, at a depth of 3400 m, hosts the ARCA (Astroparticle Research with Cosmics in the Abyss) detector, with more widely spaced DOMs optimised for detecting high-energy cosmic neutrinos in the TeV–PeV range. Its strings are 650 m long, spaced 90 m apart.[1]:3[2]:21

The KM3NeT-Fr site, at a depth of 2475 m, hosts the ORCA (Oscillation Research with Cosmics in the Abyss) detector, a more compact array with more closely spaced sensors optimised for atmospheric neutrinos in the GeV range. This will consist of 115 strings in a 20 m triangular grid, with a 9 m spacing between the DOMs in a string. Overall, the array is about 210 m in diameter, and the strings are 200 m long.[2]:6

Construction[edit]

In 2012, the first phase of the implementation of the KM3NeT research facility has started with the construction of the seabed infrastructure at the KM3NeT-Fr and KM3NeT-It sites. A prototype KM3NeT Digital Optical Module (KM3NeT-DOM) has been taking data successfully for more than a year as part of the ANTARES telescope. The KM3NeT-Fr installation site close to the ANTARES telescope is being prepared for the installation in 2016 of the first strings for the KM3NeT/ORCA detector for neutrino particle physics. At the KM3NET-It site the first prototype KM3NeT-string successfully took data for about a year. This site is being prepared for the installation of the first full strings starting end of 2015.

Relation to Other Neutrino Telescopes[edit]

For the design of the neutrino detector, KM3NeT builds on the experience of three pilot projects in the Mediterranean Sea: the ANTARES detector, the Neutrino Mediterranean Observatory (NEMO) project and the NESTOR Project. ANTARES was completed on 30 May 2008, and is the largest neutrino telescope in the northern hemisphere. In the southern hemisphere, at Antarctica, the IceCube Neutrino Observatory is already operational. Together, IceCube and KM3NeT will view the full sky and form a global neutrino observatory.

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