Direct Detection of sub-GeV Dark Matter with Semiconductor Targets (1509.01598v2)

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 ${\cal O}(1~\rm{eV})$ band gaps allow for ionization signals from dark matter 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.

• The paper introduces a novel approach for directly detecting sub-GeV dark matter via DM-electron scattering in semiconductor targets.
• It employs density functional theory to calculate crystal form factors and estimate scattering rates in silicon and germanium detectors.
• The research demonstrates that semiconductor-based detectors can achieve significantly enhanced sensitivity over traditional nuclear recoil methods.

Direct Detection of sub-GeV Dark Matter with Semiconductor Targets

The paper explores a pressing issue in dark matter (DM) physics — the direct detection of sub-GeV dark matter particles through semiconductor targets. Traditionally, direct detection experiments have primarily focused on weakly interacting massive particles (WIMPs) in the GeV to TeV mass range, utilizing their interactions with atomic nuclei. However, as experimental constraints have pushed the boundaries on these searches without significant discovery, researchers are increasingly turning toward alternative dark matter candidates, including those with masses below 1 GeV.

In the quest to identify lighter dark matter particles, experiments have begun to explore interactions involving DM-electron scattering, a promising channel that leverages the comparatively small mass and low energy thresholds of semiconductors. This marks a significant departure from the conventional approach of DM-nuclear scattering, typically requiring GeV or heavier DM particles to yield detectable nuclear recoils.

The text under consideration provides both theoretical and computational insights into detecting sub-GeV dark matter within semiconductor materials, specifically silicon and germanium. The essence of the approach lies in observing the ionization signals resulting from DM-electron scattering, facilitated by the electronic structures of these semiconductors. Notably, the underpinning physics revolves around the crystal lattice structures in semiconductors, where dark matter particles can impart enough energy to eject electrons across the band gap, thus generating detectable ionization signals.

A major thrust of the work focuses on carefully calculating the DM-electron scattering rate using solid-state physics techniques. Applying density functional theory, the authors numerically model these interactions to estimate potential scattering rates and the sensitivity of upcoming experiments like DAMIC and SuperCDMS. In this context, an essential advancement reported is the computation of a crystal form factor that encapsulates the complexities of electron behavior within the crystalline structure of the semiconductor.

The crystal form factor represents one of the paper's pivotal contributions, equipping experimental collaborations with a precise tool to estimate their sensitivity to light dark matter interactions based on the specifics of their setups. Insightfully, the paper elucidates that semiconductor targets have the potential to probe DM interactions several magnitudes better than current direct detection constraints.

The implications of this work are twofold. Practically, it pushes the boundaries of current detector technology to become sensitive to dark matter-electron scattering processes, setting the stage for future discovery possibilities in the sub-GeV mass domain. Theoretically, it enriches the understanding of potential dark matter models that involve lighter particles interacting through novel mediating forces, such as a light dark photon.

In conclusion, the research meticulously posits that detecting sub-GeV dark matter with semiconductor-based detectors is not only feasible but opens vast uncharted territories in dark matter physics. As experimental efforts progress, the interplay of theory and experiment, supported by findings such as those discussed in this paper, will be crucial in broadening our search for the elusive nature of dark matter.