The Antares telescope takes its first look at the heavens

The first detection line of the Antares neutrino telescope, lying under 2,500 meters of water, was connected by Ifremer's remotely operated robot Victor 6000 to the onshore station at La Seyne-sur-Mer (Var) on Thursday 2 March at 12:11. Several hours later, Antares took its first look at the heavens and detected its first muons [1]. The link marked the effective birth of the Antares detector, the first deep water high energy neutrino telescope in the northern hemisphere. The event rewards ten years of work by around twenty European laboratories [2], including CEA/Dapnia and the CNRS/IN2P3 laboratories, who initiated [3] the project in 1996.

The Antares [4] telescope is a neutrino detector which has two main goals: high-energy astronomy and the search for dark matter (see box below).

Neutrinos hardly interact with matter at all. The only way to detect them is by using huge detectors which are shielded from the cosmic radiation that constantly bombards any terrestrial site, resulting in major continuous background noise. Located under the sea off Toulon (Var), Antares is protected from this radiation by the natural shielding provided by 2,500 meters depth of seawater. Photodetectors, the eyes of Antares, use a large volume of seawater to detect the very faintly luminous trails produced by muons coming up from below. The muons are produced by the interaction with the Earth's crust of neutrinos which have passed through the Earth. They can be detected because of the total darkness reigning at such immense depths. So Antares looks right through the Earth and observes the skies of the southern hemisphere, including the galactic center, which is the seat of intensely energetic phenomena.

The photodetectors are grouped in threes along umbilical cables which are 450 meters high, which carry signals as well as energy. A total of 900 such "eyes", distributed along 12 lines covering an area of around 200 m x 200 m on the sea floor, will be scrutinizing the Universe by the end of 2007. Each line is connected to a junction box, which is linked by a 40-kilometer long electro-optical cable to the onshore station at the Institut Michel Pacha in La Seyne-sur-Mer. The installation of the Antares telescope benefited from Ifremer's logistics and expertise.

In addition, Antares forms a permanent multidisciplinary submarine scientific facility, recording both oceanographic data, including observation of the deep sea marine environment and bioluminescent phenomena, as well as geophysical data: for instance, a seismograph has been recording earthquakes for the past year.

SIDEBAR

Antares has been designed to detect high-energy cosmic phenomena. Over the last few decades, a large number of objects have been discovered by astronomers, some of which are the seat of cataclysmic phenomena that emit photons, charged particles and very high-energy neutrinos. However, photons are absorbed by matter, which limits the depth of space which can be observed, while particles that are not too highly charged with energy are deflected by the galactic and extragalactic magnetic fields, which makes detecting point sources, and therefore astronomy, very difficult.

On the other hand, cosmic neutrinos are elementary particles that only interact weakly with matter. They thus journey for great distances through the Universe without being absorbed by the intergalactic medium, traveling in a straight line from the core of cosmic accelerators without being deflected. They therefore make it possible to probe the distant universe and study the sources that give rise to very high-energy cosmic radiation. Antares may also be able to detect lower-energy neutrinos originating in the accumulation of dark matter at the center of the Earth, the Sun or our Galaxy.

First discovered 70 years ago, dark matter is currently one of the major problems in cosmology. We still have no idea what makes up 95% of our Universe! The nature of the missing matter and energy is completely unknown, but might partly be made up of massive elementary particles called WIMPs (weakly interacting massive particles). The so-called "supersymmetry" theory predicts their existence, which has not yet been verified. It is possible that these particles accumulate at the center of massive objects such as the Earth or the Sun. Since WIMPs are simultaneously particles and anti-particles it is thought that they end up by annihilating each other, producing a burst of energy and particles, including neutrinos.

To find out more:      http://antares.in2p3.fr

Notes:

[1] The muon is a particle similar to the electron, and can travel through large quantities of matter. Above a certain speed, it produces in water a trail of blue light, known as Cherenkov radiation.

[2] Over 150 researchers, engineers and technicians from the following laboratories: CPPM (CNRS/IN2P3 univ. de la Méditerranée Aix-Marseille II); DSM/Dapnia (CEA/Saclay); GRPHE (univ. de Haute-Alsace, Mulhouse); IPHC (CNRS/IN2P3 ULP Strasbourg) ; APC (Univ. Paris VII, CNRS, CEA, observatoire de Paris) ; ITEP (Moscow, Russia); IFIC (CSIC/univ. of Valencia, Spain); NIKHEF, KVI, universities of Amsterdam and Utrecht (Netherlands); INFN-Italy (univ. of Bari, Bologna, Catania, Genova, Pisa, Roma, laboratory LNS-Catania); univ. of Erlangen (Germany); Géosciences Azur (CNRS, IRD, UNSA, UPMC); COM (CNRS/INSU univ. de la Méditerranée Aix-Marseille II); LAM (CNRS/INSU univ. de Provence); Ifremer (Toulon/La Seyne-sur-Mer center and Brest center).

[3] More precisely, the Centre de physique des particules de Marseille (CPPM ) (Marseille Center for Particle Physics), a CNRS/IN2P3 and université de la Méditerranée joint research unit (acting as local support for the collaboration), and CEA/Dapnia, Laboratory for research into the fundamental laws of the Universe.

[4] Funding for the Antares project is provided by contributions from CEA (DSM/Dapnia) and CNRS/IN2P3; the Alsace Region, the Provence Alpes Côte d'Azur Region, the Var Department, the city of La Seyne-sur-Mer; the European Union; and from five countries (Netherlands, Germany, Italy, Spain and Russia).