Nuclear Physics of Dark Matter Detection

Abstract

We describe the elastic scattering of weakly interacting dark matter particles from nuclei, with laboratory detection in mind. We focus on the lightest neutralino (a neutral fermion predicted by supersymmetry) as a likely candidate and discuss the physics needed to calculate its elastic scattering cross section and interpret experimental results. Particular emphasis is placed on a proper description of the structure of the proposed detector nuclei. We include a brief discussion of expected count rates in some detectors.

Nuclear structure aspects of spin-independent WIMP scattering off xenon

“…The SI interaction of WIMPs with nuclei, assuming spin 1/2 neutralinos, is described by the low-momentumtransfer Lagrangian [14] …”

“…As in Ref. [14], we take the hadronic current of the nucleons to be purely isoscalar with coupling c 0 . We take into account only the leading one-body currents, so that the scalar nuclear current is a sum over single nucleons,…”

“…However, experimental results are commonly presented in terms of "neutron-only" (a 0 = −a 1 = 1) and "proton-only" (a 0 = a 1 = 1) structure factors S n (u) and S p (u), because these coupling combinations are more sensitive to neutrons and protons, respectively. For vanishing momentum transfer, q = 0 (u = 0), and considering only one-body currents, the SD "neutron-only" and "proton-only" structure factors are proportional to the square of the expectation values of the neutron and proton spins [14]. These are given for both calculations in Table III.…”

“…[14]. In addition, a reliable description of the nuclear states involved in the scattering process is needed.…”

Magnetic fluffy dark matter

“…While the helm form factor is expected to be a good approximation for the factor by which the cross section decreases for non-zero momentum transfer in spin independent interactions, the nuclear magnetic dipole moment form-factor deserves more careful treatment. The usual thin-shell model for spin-dependent interactions need not be a good approximation for heavier nuclei [33]. We follow Ref.…”