ANTARES (telescope)

ANTARES is the name of a neutrino telescope residing in the Mediterranean Sea off the coast of Toulon, France. It will observe neutrinos from the Southern Hemisphere to complement the northern hemisphere work of IceCube. The name comes from Astronomy with a Neutrino Telescope and Abyss environmental RESearch project; the acronym also being the name of a prominent star. Other neutrino telescopes designed for use in the nearby area include the Greek NESTOR telescope and the Italian NEMO telescope, which are both in early design stages.

The array contains a set of twelve separate vertical strings of photomultiplier tubes. Each one has 75 optical modules and is about 350 meters long. They are anchored at the bottom of the sea at a depth of about 2.5 km, roughly 70 meters apart from each other. Unlike traditional telescopes, ANTARES works by facing downward, into the earth. This is because the earth is nearly transparent to neutrinos but not to the atmospheric muons, which produce the most important physics background in a neutrino telescope. When neutrinos enter the southern hemisphere of the earth, they usually continue traveling directly through it. On rare occasions, a few muon neutrinos interact with the water in the Mediterranean Sea. When this happens, they produce a high energy muon. As the muon passes through the water, it emits Cherenkov radiation, which ANTARES expects to detect on the photomultiplier tubes.

In contrast to the South Pole neutrino telescopes AMANDA and IceCube, ANTARES uses water instead of ice as its Cherenkov medium. As light in water is less scattered than in ice this results in a better resolving power. On the other hand, water contains more sources of background light than ice (radioactive isotopes potassium-40 in the sea salt and bioluminescent organisms), leading to a higher energy thresholds for ANTARES with respect to IceCube and making more sophisticated background-suppression methods necessary.

Construction history

The construction of ANTARES has been completed May 30th, 2008, two years after the first string was deployed.Initial testing began in 2000. Equipment indirectly related to the detector such as a seismometer were deployed in 2005. The first string of photomultiplier tubes was moved into place in February 2006. In September 2006 the second line was successfully connected. Lines 3, 4 and 5 were deployed at the end of 2006 and connected in January 2007. This was an important step that made Antares the biggest neutrino telescope in the Northern hemisphere (surpassing the Baikal neutrino telescope). Lines 6, 7, 8, 9, and 10 were deployed between March and early November 2007 and connected in December 2007 and January 2008.

Deployment and connection of the detector are performed in cooperation with the French oceanographic institute, IFREMER, currently using the ROV Victor, for some past operations the submarine Nautile.

Experimental goals

The ANTARES project is the counterpart to IceCube Neutrino Detector. The detection principles of the two projects are very similar, and they point toward opposite hemispheres. ANTARES will detect neutrinos from high energy origin, particularly in the range from $10^\{11\}$ to $10^\{14\}$ electron-volts (100 GeV - 100 TeV). Over several years of operation, it may be able to produce a map of the neutrino flux from cosmic origins in the southern hemisphere. Of particular interest is the detection of astrophysical point sources of neutrinos, possibly in correlation with observations in other bands (such as gamma rays sources observed by the HESS telescope in Namibia, which has a common field of view with ANTARES).

Apart from this astro-particle physics aspect, the ANTARES telescope will also tackle some fundamental problems in particle physics, such as the search for dark matter in the form of neutralino annihilation in the sun ("normal" solar neutrinos being outside the energy range of ANTARES) or the galactic centre. Due to the very different methods employed, its expected sensitivity is nearly complementary to the direct dark matter searches performed by various experiments such as DAMA, CDMS and at the LHC. Detection of neutralino signals would also confirm supersymmetry. Other possible "exotic" phenomena that could be measured by ANTARES include nuclearites or magnetic monopoles.

Additional Instrumentation

In addition to the main optical detector for cosmic neutrinos, the ANTARES experiment also houses a number of instruments for the study of the deep sea environment, such as salinity and oxygen probes, sea current profilers and instrumentation for the measurement of light transmission and sound velocity. Also, a camera system has been installed for the automatic tracking of bioluminescent organisms. Results from these instruments, while also important for the calibration of the detector, will be shared with ocean science institutes involved in the ANTARES collaboration. While the ANTARES detector contains an acoustic positioning system for the alignment of the free-floating detector lines, it also houses a separate dedicated acoustic detection system AMADEUS, which will comprise 6 converted ANTARES storeys with hydrophones to evaluate the possibility for the acoustic detection of neutrinos in the deep sea. The first 3 of these acoustic storeys have been included in the "instrumentation line", the other 3 on the 12th line.

References

[http://antares.in2p3.fr/ ANTARES home]

[http://www.ifremer.fr/anglais/ IFREMER homepage (in english)]

[http://www.km3net.org KM3NeT neutrino telescope]