Dark matter - the axion gets more likely

The hypothetical axion particle was born in the eighties as a consequence of an assumption about the existence of a broken hidden symmetry associated with the strong interaction. We know that the axion probability to interact with ordinary matter is very low because no axion has ever been detected in particle colliders so far. In 1987 a cosmic event: the explosion of a supernova, allowed the physicists to put a limit on the mass of the axion: less than 10^-3 eV. So light particles are usually very stable, an axion could exist for 10⁴⁵ years and then could decay in 2 microwave photons. The axions could have been created in huge quantities at the time of the Big-bang and might composed now what we called dark matter. The ADMX device (axion dark matter experiment) aims at detecting microwave photons from axion decay. The ADMX device is composed of a magnet delivering an intense magnetic field (∼ 8 tesla) inside a microwave cavity designed to favor axion decay and of a SQUID (superconducting quantum-interference device) amplifier to amplify the tiny magnetic signal due to the presence of microwave photons. One of the challenge was to annihilate the magnetic field of the magnet near the SQUID amplifier in order to be able to detect microwave photons. The ADMX principle has been validated and tested, and ADMX generation 2, is now operating for searching axions in the mass range between 1 and 40 10^-6 eV. (A.C.)