Probing the Dark Matter EFT with QUEST-DMC: Projected Sensitivities and Attenuation Ceilings

TL;DR

This paper discusses projected sensitivities of the QUEST-DMC surface-based experiment using superfluid helium for detecting sub-GeV dark matter, considering various interaction models and environmental attenuation effects.

Contribution

It introduces a novel experimental approach with low recoil thresholds and provides comprehensive projections within the non-relativistic EFT framework, including atmospheric attenuation effects.

Findings

Projected sensitivity to sub-GeV dark matter interactions.

Identification of an interaction-dependent sensitivity ceiling due to atmospheric attenuation.

Mapping of non-relativistic EFT results onto relativistic dark matter models.

Abstract

This proceedings contribution summarises projected constraints from the QUEST-DMC concept, a surface-based direct-detection experiment using superfluid $^3$He operated below the millikelvin regime and instrumented with nanomechanical resonators read out by SQUIDs. The low recoil-energy threshold (down to sub-eV for the SQUID configuration) enables sensitivity to sub-GeV dark matter across a wide set of interaction structures beyond the canonical spin-independent and spin-dependent limits. We present projections in the non-relativistic Effective Field Theory (EFT) framework, scanning the standard set of fourteen Galilean-invariant operators and expressing reach in terms of effective dark matter-nucleon (or dark matter-neutron) cross sections. Because QUEST-DMC operates at the surface, we also account for suppression of the incident flux due to scattering in the atmosphere and Earth, which produces an interaction-dependent sensitivity ceiling at large couplings. Finally, we outline how the non-relativistic results map onto representative relativistic EFT dark matter-nucleon bilinears, enabling a compact interpretation of the projected reach in terms of UV-motivated coupling structures.