Abstract
We discuss several low-energy backgrounds to sub-GeV dark-matter searches, which arise from high-energy particles of cosmic or radioactive origin that interact with detector materials. We focus, in particular, on Cherenkov radiation, transition radiation, and luminescence or phonons from electron-hole pair recombination and show that these processes are an important source of backgrounds at both current and planned detectors. We perform detailed analyses of these backgrounds at several existing and proposed experiments based on a wide variety of detection strategies and levels of shielding. We find that a large fraction of the observed single-electron events in the SENSEI 2020 run originate from Cherenkov photons generated by high-energy events in the Skipper charge coupled device and from recombination photons generated in a phosphorus-doped layer of the same instrument. In a SuperCDMS HVeV 2020 run, Cherenkov photons produced in printed-circuit boards located near the sensor likely explain the origin of most of the events containing 2–6 electrons. At SuperCDMS SNOLAB, radioactive contaminants inside the Cirlex located inside or on the copper side walls of their detectors produce many Cherenkov photons, which could dominate the low-energy backgrounds. For the EDELWEISS experiment, Cherenkov or luminescence backgrounds are subdominant to their observed event rate but could still limit the sensitivity of their future searches. We also point out that Cherenkov radiation, transition radiation, and recombination could be a significant source of backgrounds at future experiments aiming to detect dark matter via scintillation or phonon signals. We also discuss the implications of our results for the development of superconducting qubits and low-threshold searches for coherent neutrino scattering. Fortunately, several design strategies to mitigate these backgrounds can be implemented, such as minimizing nonconductive materials near the target, implementing active and passive shielding, and using multiple nearby detectors.
- Received 18 December 2020
- Revised 12 November 2021
- Accepted 15 November 2021
DOI:https://doi.org/10.1103/PhysRevX.12.011009
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Detecting dark-matter particles in the laboratory is crucial to reveal its elusive nature. In recent years, tremendous progress has been made in the search for dark-matter particles with masses less than that of a proton. However, the first generation of experiments see many background events of unexplained origin, among which dark-matter signals may be hiding. To fully realize the potential of experiments and clear the path toward the direct detection of dark matter, it is crucial to identify the origin of these events. Here, we identify three unexplored processes that surreptitiously mimic dark-matter signals at laboratories.
Specifically, we explore three processes that arise when high-energy particles interact with materials in dark-matter detectors: Cherenkov radiation, transition radiation, and luminescence or phonons from electron-hole recombination. We demonstrate that the event rates of these processes at several experiments are so large that they not only explain a large fraction of the observed event rates but also significantly impede the discovery of many dark-matter candidates. To solve this issue, we provide clear methodologies to calculate the effect of these processes and propose several important design strategies to mitigate them.
The tools and ideas that we provide will have profound consequences for the development of improved data analyses and for the design of future dark-matter experiments. Moreover, our findings could also have an important impact on the development of quantum computers and neutrino detectors, whose performance can be affected by the same processes.
