Dark Matter: Direct Detection

Abstract

Abstract. Solving the Dark Matter enigma represents one of the key objectives of contemporary physics. Recent astrophysical and cosmological measurements have unambiguously demonstrated that ordinary matter contributes to less than 5% of the energy budget of our Universe, and that the nature of the remaining 95% is unknown. Weakly Interacting Massive Particles (WIMPs) represent the best motivated candidate to fill the Dark Matter gap, and direct detection Dark Matter experiments have recently reached sensitivities allowing them to sample a first part of supersymmetric models compatible with accelerator constraints.Three cryogenic experiments currently provide the best sensitivity, by nearly one order of magnitude, to WIMP interactions. With systematic uncertainties far less severe than other present techniques, the next generation of cryogenic experiments promises two orders of magnitude increase in sensitivity over the next few years. The present results, perspectives and experimental strategies of the main direct detection experiments are presented. Challenges met by future ton-scale cryogenic experiments in deep underground sites, aiming at testing most of the SUSY parameter space, are critically discussed.The Dark Matter enigma was first formulated by Fritz Zwicky [1] in the early thirties. From observations of the velocity dispersion of eight galaxies in the Coma cluster, Zwicky found that the velocities of these galaxies were far too large to allow them to remain trapped in the cluster's gravitational well. Converting the observed velocity dispersion in terms of mass deficit, Zwicky concluded that visible stars only contribute 0.5% of the total mass present in the Coma cluster. Today, although the reevaluations of the distance scale and the Hubble parameter lead to a revised estimate of the missing mass factor, Zwicky's observations appear as one of the most astonishing and profound insights of modern physics.