Direct detection of sub-GeV dark matter with semiconductor targets

Abstract

Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their O(1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcoming several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark, with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. The searches we propose will probe vast new regions of unexplored dark matter model and parameter space.

Detecting superlight dark matter with Fermi-degenerate materials

“…Greater sensitivity to lighter DM for a given deposited energy can be achieved via inelastic processes, such as electron ionization or excitation [20][21][22]. In this case, the process may be catalyzed if the incoming DM kinetic energy, E kin = m X v 2 X /2, exceeds the…”

“…Note that the electron velocity does play a role in DM scattering off electrons in a semi-conductor or noble gas as well [22]. In such scatterings, for DM heavier than an MeV, the electron velocity is not a necessary ingredient to catalyze the process and extract all of the DM energy in the scattering, but nevertheless it does impact the kinematics, since the electron velocity, v i,T ∼ α Z with Z the electric charge of the nucleus, is larger than the velocity of the DM.…”

“…For comparison, the gray dot-dashed curve depicts the expected sensitivity utilizing electron ionization in a germanium target as obtained in ref. [22].…”

“…We also show the projected reach curves utilizing electron ionization techniques in a semi-conductor germanium target (silicon performs similarly) as obtained in ref. [22], translated toσ DD of eq. (3.11), shown in the thick gray dot-dashed curves.…”

The 17 MeV Anomaly in Beryllium Decays and U(1) Portal to Dark Matter

“…The projected sensitivities for Silicon and Germanium targets with improved Q th = 5e − are presented as green solid line and orange dashed line, respectively [49]. The red shaded region is the theoretical predictions of σ χe corresponding to the range of 10 −6 < |a e | < 10 −5 .…”