Model-independent form factors for spin-independent neutralino–nucleon scattering from elastic electron scattering data

Abstract

Theoretical calculations of neutralino cross sections with various nuclei are of great interest to direct dark matter searches such as CDMS, EDELWEISS, ZEPLIN, and other experiments. These cross sections and direct detection rates are generally computed with standard, one or two parameter model-dependent nuclear form factors, which may not exactly mirror the actual form factor for the particular nucleus in question. As is well known, elastic electron scattering can allow for very precise determinations of nuclear form factors and hence nuclear charge densities for spherical or nearspherical nuclei. We use charge densities derived from elastic electron scattering data to calculate model independent form factors for various target nuclei important in dark matter searches, such as Si, Ge, S, Ca and others. We have found that for nuclear recoils in the range of 1-100 keV significant differences in cross sections and rates exist when the model independent form factors are used. DarkSUSY, a publicly-available advanced numerical package for neutralino dark matter calculations, has been modified to include these model independent form factors for select nuclei; these modifications will be available with the code in the next public release, and will allow for a more accurate determination of the neutralino spin independent scattering cross sections and rates with nuclear detectors.

Signatures of large composite Dark Matter states

“…Figure 1. Form factor for nuclear charge density (black) of 70 Ge nucleus, as derived from electron scattering data [20]. Blue (dashed) curve is standard Helm parameterisation, red (dot-dashed) curve is constant-density approximation.…”

“…Figure 1 shows an example of the form factor corresponding to the nuclear charge density for the particular isotope 70 Ge [20], as inferred from electron scattering data. Generally, and in this specific case, the first few peaks and troughs of SM nuclear form factors are well-approximated by the 'Helm' functional form…”

Determining Nuclear Form factor for Detection of Dark Matter in Relativistic Mean Field Theory

“…The Helm form factor is the form factor which is most commonly used in directly searching for dark matter [18,21,22].…”

“…The three parameters are determined in the elastic electron scattering experiments [23]. The analytical form of the form factor is given as [18]:…”

“…In another model, the charge density is described as a sum of the Fourier-Bessel functions up to a certain cutoff radius R. The coefficients a ν of the Bessel expansions are directly extracted from the elastic electron scattering experiments. The charge density and form factor are given [12,18]:…”