Direct detection of MeV-scale dark matter utilizing germanium internal amplification for the charge created by the ionization of impurities

Abstract

Light, MeV-scale dark matter (DM) is an exciting DM candidate that is undetectable by current experiments. A germanium (Ge) detector utilizing internal charge amplification for the charge carriers created by the ionization of impurities is a promising new technology with experimental sensitivity for detecting MeV-scale DM. We analyze the physics mechanisms of the signal formation, charge creation, charge internal amplification, and the projected sensitivity for directly detecting MeV-scale DM particles. We present a design for a novel Ge detector at helium temperature (∼ 4 K) enabling ionization of impurities from DM impacts. With large localized E-fields, the ionized excitations can be accelerated to kinetic energies larger than the Ge bandgap at which point they can create additional electron-hole pairs, producing intrinsic amplification to achieve an ultra-low energy threshold of ∼ 0.1 eV for detecting low-mass DM particles in the MeV scale. Correspondingly, such a Ge detector with 1 kg-year exposure will have high sensitivity to a DM-nucleon cross section of ∼ 5 × 10 −45 cm 2 at a DM mass of ∼ 10 MeV/c 2 and a DM-electron cross section of ∼ 5 × 10 −46 cm 2 at a DM mass of ∼ 1 MeV/c 2 .

The impact of the charge barrier height on Germanium (Ge) detectors with amorphous-Ge contacts for light dark matter searches

“…This enables Ge detectors to be used for detecting low mass WIMPs of a few GeV/c 2 . More recently, a Ge detector utilizing internal charge amplification for the charge carriers created by the ionization of impurities has been demonstrated theoretically to be a promising new technology for detecting MeV-scale dark matter [31].…”

“…In order to directly detect MeV-scale dark matter, a detector with the ability to measure a single electron-hole (e-h) pair is required, since both electronic recoils and nuclear recoils induced by MeV-scale dark matter are in the range of sub-eV to 100 eV [1]. Mei et al has suggested direct detection of MeV-scale DM utilizing germanium internal charge amplification (GeICA) for the charge created by the ionization of impurities [31]. GeICA can reach a detection energy threshold as low as 0.1 eV, allowing a large portion of both electronic recoils and nuclear recoils in the range of sub-eV to 100 eV [1,31] induced by DM to be accessible.…”

MeV dark matter complementarity and the dark photon portal

“…Dark matter at the MeV scale is an interesting possibility, offering a rich phenomenology [4]. The topic has witnessed increasing interest in light of null results in the search for WIMPs [17] and of the many upcoming experimental probes for MeV-scale dark matter [18][19][20][21][22][23]. Several MeV dark matter studies have been conducted in the literature, e.g.…”

Mapping the neutrino floor for direct detection experiments based on dark matter-electron scattering

“…As mentioned in Sec. III C, adding dopants to the Germanium crystal can lower the ionization energy and probe lower values of M χ [43]. The impact of the discovery limit for several doping techniques could be calculated in order to probe lower DM masses.…”

“…It is possible to lower the band-gap energy by adding dopants to the Germanium crystal as discussed in [43]. Phonons with ionization energies as low as ∼0.01 eV can ionize or excite impurities and create charge carriers, though the sub-eV recoil energies are small enough that they can be obscured by electronic noise of signal digitization.…”