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Established on the mediterranean seabed, at nearly 2500 m depth, 40 km off Toulon, ANTARES (Astronomy with a Neutrino Telescope and Abyss environmental RESearch) is the first operational submarine neutrino telescope. Its 12 lines, equipped with almost 900 photomultiplier tubes, scrutinize the abysses since May 2008 in order to discern photons produced by Čerenkov effect along the path of ultra-relativistic muons.

Illustration of the detection principle of an astrophysical neutrino by ANTARES.
(©2005 : Alexander Kappes)

The identification of these photons is made difficult by the presence of Čerenkov light due to byproducts of natural radioactive nuclei decays (mostly potassium 40), and by bioluminescence emitted by submarine organisms. Good use is however made of these informations for studies of the marine environment, making ANTARES a unique kind of ocean observatory.

Some of the most violent astrophysical phenomenons escape from the reach of traditional instruments, light being absorbed before to reach Earth. Interacting only very weakly with matter, the neutrino is an ideal candidate for studying such phenomenons. It is the first stake of neutrino telescopes to prove the existence of very high energy neutrino (above 1 TeV) of astrophysical origine and to associate them their source. The ANTARES telescope is one of the pioneers of this discipline, and the first one in the northern hemisphere.

The neutrino itself is particularly difficult to detect, but its interaction with the earth may produce a muon, the detection of which is fairly simple. The huge amount of muons produced by the interaction of cosmic particles with the atmosphere makes this task tougher, although the water above ANTARES attenuates considerably the quantity of atmospheric muons. The upgoing direction of muons coming from the interaction of neutrinos with Earth allows to distinguish them from such atmospheric muons. Unfortunately, atmospheric neutrinos, also produced by the interaction of cosmic rays with the atmosphere, constitute an irreducible background.

The scientific potential of ANTARES does not, however, resume itself to search for very high energy neutrinos of astrophysical origin and investigation of the submarine world : the observation of lower energy neutrinos (from a few tens to a few hundreds of GeV), the existence of which is known, should allow to improve the knowledge of neutrinos oscillations parameters. An accumulation of relatively low energy neutrinos from a particular direction could also, according to some theoretical models, be an indication of the presence of dark matter.

Activities of the ANTARES group at the LPC (Laboratoire de Physique Corpusculaire, Clermont-Ferrand) currently concentrate on these latter aspects.