A method for directional detection of dark matter using spectroscopy of crystal defects

We propose a method to identify the direction of an incident weakly interacting massive particle (WIMP) via induced nuclear recoil. Our method is based on spectroscopic interrogation of quantum defects in macroscopic solid-state crystals. When a WIMP scatters in a crystal, the induced nuclear recoil creates a tell-tale damage cluster, localized to within about 50 nm, with an orientation to the damage trail that correlates well with the direction of the recoil and hence the incoming WIMP. This damage cluster induces strain in the crystal, shifting the energy levels of nearby quantum defects. These level shifts can be measured optically (or through paramagnetic resonance) making it possible to detect the strain environment around the defect in a solid sample. As a specific example, we consider nitrogen vacancy centers in diamond, for which high defect densities and nanoscale localization of individual defects have been demonstrated. To localize the millimeter-scale region of a nuclear recoil within the crystal due to a potential dark matter event, we can use conventional WIMP detection techniques such as the collection of ionization/scintillation. Once an event is identified, the quantum defects in the vicinity of the event can be interrogated to map the strain environment, thus determining the direction of the recoil. In principle, this approach should be able to identify the recoil direction with an efficiency greater than 70% at a false-positive rate less than 5% for 10 keV recoil energies. If successful, this method would allow for directional detection of WIMP-induced nuclear recoils at solid-state densities, enabling probes of WIMP parameter space below the solar neutrino floor. This technique could also potentially be applied to identify the direction of particles such as neutrons whose low scattering cross section requires detectors with a large target mass.

Figure 1

Left: Event identified by conventional methods. Right: Section of interest separately studied by superresolution methods.

Figure 2

A typical damage cluster shape from a 30 keV ion injected into a crystal from a TRIM simulation. The cluster is well correlated with the direction of the injected ion. The ion should be thought of as the recoiling nucleus, coming from a WIMP scattering event. In this figure, the ion has been injected from the left.

Figure 3

TRIM simulation results in diamond are plotted for different initial recoil energies. Left: The distribution of damage asymmetries is shown. An example asymmetry cut is shown with a 5% false-positive rate resulting in an efficiency of $\sim 70\%$. Right: The angular difference between the initial recoil direction and the overall damage direction is shown. The two directions are more correlated for higher initial recoil energies.