Direct dark matter detection: Overview and update

Abstract

It is well-established that our Galaxy, as well as external galaxies, contains a substantial amount of dark matter that is deduced primarily via gravitational effects. Null results from searches for gravitational microlensing along the line-of-sight towards the Magellanic clouds imply that no more than ∼ 10% of the Galactic dark matter halo is comprised of compact objects such as planets or low-mass stars [1, 2]. The dominant component of the dark matter must be smooth enough as to not cause an excess of microlensing events, and nearly cold and collisionless so as to satisfy constraints from the large scale distribution of galaxies and the Cosmic Microwave Background [3]. Cold, collisionless Weakly-Interacting Massive Particles (WIMP) in thermal equilibrium in the early Universe may freeze-out with a relic abundance of order the observed dark matter density, ΩDM = 0.227 −0.016. Elastic scattering processes between WIMPs and quarks may lead to observable signals in low background underground detectors [4]. It is therefore prudent to search for particles with these properties to determine whether they constitute a significant fraction of the mass of the Galactic halo. This contribution reviews principles, results, and future prospects for direct searches of WIMP dark matter particles. It is intended to provide a theoretical overview and framework for the various experimental results discussed at this meeting. For details on each of the experiments, please see the respective presentations 1 and proceeding contributions.