Direct detection of WIMPs

Abstract

If the Milky Way’s DM halo is composed of WIMPs, then the WIMP flux on the Earth is of the order of 105(100 GeV/mχ)cm−2 s−1. This flux is suf- ficiently large that, even though the WIMPs are weakly interacting, a small but potentially measurable fraction will elastically scatter off nuclei. Direct detection experiments aim to detect WIMPs via the nuclear recoils, caused by WIMP elastic scattering, in dedicated low background detectors [988]. More specifically they aim to measure the rate, R, and energies, ER, of the nuclear recoils (and in directional experiments the directions as well). In this chapter we overview the theoretical calculation of the direct detection event rate and the potential direct detection signals. Section 17.2 outlines the calculation of the event rate, including the spin-independent and spin-dependent contributions and the hadronic matrix elements. Section 17.3 discusses the astrophysical input into the event rate calculation, including the local WIMP velocity distribution and density. In Section 17.4 we describe the direction detection signals, specifically the energy, time and direction dependence of the event rate. Finally in Section 17.5 we discuss the predicted ranges for the WIMP mass and cross-sections in various particle physics models.