EPFL deep down in Antarctica
Ten years will have been required to set up the world’s largest neutrino observatory. IceCube is now ready and can begin its mission: to decipher the universe.
40,000,000,000,000,000 neutrinos pass through the human body every second. They are so small that they almost never interact with the matter around us. And yet, being able to detect them would give us extremely valuable information about the universe and the objects it is made of. Consequently, the international scientific community decided to build IceCube, the Antarctica observatory with the goal of improving the observation of neutrinos.
EPFL’s Laboratory for High Energy Physics (LPHE), and in particular astroparticle physicists, took part in this fascinating adventure, with the construction work being completed on December 18, 2010. Located at the pole of the earth, this innovative detector is dedicated to the study of the fundamental properties of particles, whose origin describes the most spectacular phenomena of the universe, such as supernovae or gamma-ray bursts.
“In the last five years, during the short austral summer season, 86 bore holes of a depth of 2500m were drilled and equipped with 5000 optical detection modules. These modules are the “eyes” of the IceCube detector, which observes one cubic kilometer of ice near the geographic South Pole”, explains Mathieu Ribordy, professor at the LPHE.
IceCube uses the Cerenkov effect, the equivalent of the supersonic bang for light. The latter moves at a speed of about 300,000 km/s in space, but slower in material media. As a result, along the trajectory of charged particles, which travel faster than light in the material media, a luminous bluish flash is emitted. This flash is visible by detectors within a one-hundred meter range in the very pure ice of the South Pole. This is how we are able to materialize the passage of a charged particle after interaction with a neutrino. The ice in the depths of Antarctica presents the advantage of being transparent and exceptionally clean, as well as having low radioactivity, which enables us to avoid certain types of interference during observation. It is therefore the ideal candidate for a neutrino observatory.
“Even if the number of neutrinos which reach the earth is prodigious, those which interact with the ice and cause a Cerenkov effect are rare. In order to put all the odds in our favor, we have built a huge detector measuring one cubic kilometer; that is one billion tons of ice. And in spite of this gigantic size, we still only observe 300 flashes a day. Yet it’s a record!”, adds Mathieu Ribordy.
With a detector as sensitive as IceCube, scientists at last hope to observe neutrinos from sources located beyond the sun, and thus better understand the universe surrounding us. It will be mainly a question of determining the nature of dark matter and to at last understand the origin of cosmic rays.
Link: http://icecube.wisc.edu/