Abstract
We propose two-dimensional materials as targets for direct detection of dark matter. Using graphene as an example, we focus on the case where dark matter scattering deposits sufficient energy on a valence-band electron to eject it from the target. We show that the sensitivity of graphene to dark matter of MeV to GeV mass can be comparable, for similar exposure and background levels, to that of semiconductor targets such as silicon and germanium. Moreover, a two-dimensional target is an excellent directional detector, as the ejected electron retains information about the angular dependence of the incident dark matter particle. This proposal can be implemented by the PTOLEMY experiment, presenting for the first time an opportunity for directional detection of sub-GeV dark matter.
Highlights
The Weakly Interacting Massive Particle (WIMP) is currently the dominant theoretical paradigm for dark matter (DM), and has guided experimental search efforts in recent decades
Direct detection experiments, which search for DM-nucleus collisions, are currently targeting the WIMP parameter space [1,2,3,4,5,6,7]
Simulating the full 3-dimensional DM velocity distribution g(v) in the Standard Halo Model (SHM), we find the rate in the forward direction is approximately a factor of 2 larger than in the backward direction for DM masses from 10 MeV to 10 GeV
Summary
The Weakly Interacting Massive Particle (WIMP) is currently the dominant theoretical paradigm for dark matter (DM), and has guided experimental search efforts in recent decades. This Letter proposes an alternative approach using two-dimensional (2D) materials as targets In this setup, an incident DM particle can deposit sufficient energy on a valence electron to eject it from the target. The energy and direction of the recoiling electron is directly measured with a combination of position measurements, time-of-flight, and energy deposition in a calorimeter This is in contrast to scattering in bulk targets, where the scattered particle (nucleus or electron) produces secondary excitations before measurement [2,30,26,27], erasing the initial directional information in the scattering. There are currently no feasible proposals for directional detection of sub-GeV DM [32], making the use of 2D targets a powerful tool in pushing sensitivities to lower DM masses. We will describe a potential experimental realization using the PTOLEMY experiment [33]
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