Using atomic phenomena to search for GeV scale dark matter*

The vast majority of the effort to detect dark matter has focused on weakly interacting massive particles (WIMPs), with masses on the order of ~10 – 1000 GeV [1]. WIMPs in that mass range may scatter off atomic nuclei leaving detectable recoil energy in experiments. However, this represents only a tiny sliver of the possible mass range for dark matter particles, which may have masses down to < ~ 10^-20 eV. Current experiments are blind to the majority of this parameter space. Taking advantage of atomic (rather than nuclear) phenomena, however, may drastically increase the range of masses we may search for.

As the DM mass drops much below the nucleus mass (electrons, leading to observable ionisations [2]. As the DM mass drops below that of the electron (<~MeV), there are no detectable electron recoils, however, a detectable signal may instead come from DM absorption [3]. Finally, as the DM mass drops below the ~eV scale, it behaves as a classical radiation field. Then, the observable effect comes in the form of atomic interactions with the classical DM field, such as energy shifts caused by dark-matter-induced effective variation of fundamental constants.

Here, we focus on dark matter in the GeV range, which until recently has been one of the least studied mass ranges for dark matter. We investigate the possibility for the direct detection such DM in scintillation experiments. We demonstrate that the potential scintillation event rate is much larger than is naively expected, meaning competitive searches can be performed using the conventional scintillation signals. We also demonstrate the crucial importance of accurately treating the atomic wavefunctions in calculations; common approximations lead to underestimation by many orders-of-magitude in some cases. This is important given the recent and upcoming very large liquid xenon detectors, and means the search for dark matter may be geatly extended using existing and upcoming experiments.

[1] XENON, PRL 129, 161805 (2022); J. Cos. Astro. 11, 031 (2020).

[2] BMR, Flambaum, Gribakin, PRL 116, 023201 (2016); BMR, Dzuba, Flambaum, Pospelov, Stadnik, PRD 93, 115037 (2016).

[3] Tran, Derevianko, Dzuba, Flambaum, PRL 127, 081301 (2021).

[4] Caddell, BMR (2023); BMR, Flambaum, PRD 100, 063017 (2019).