A Path to the Direct Detection of sub-GeV Dark Matter Using Calorimetric Readout of a Superfluid $^4$He Target

TL;DR

This paper proposes a novel superfluid helium-based calorimetric detector for sub-GeV dark matter, leveraging unique phonon and scintillation detection methods to improve sensitivity and background discrimination.

Contribution

It introduces a new detection concept combining superfluid helium with calorimetric sensors, enabling lower energy thresholds and enhanced background rejection for dark matter searches.

Findings

Projected sensitivity covers new dark matter parameter space.

Simulations show effective background discrimination.

Potential for sub-kg target mass to detect light dark matter.

Abstract

A promising technology concept for sub-GeV dark matter detection is described, in which low-temperature microcalorimeters serve as the sensors and superfluid $^4$He serves as the target material. A superfluid helium target has several advantageous properties, including a light nuclear mass for better kinematic matching with light dark matter particles, copious production of scintillation light, extremely good intrinsic radiopurity, a high impedance to external vibration noise, and a unique mechanism for observing phonon-like modes via liberation of $^4$He atoms into a vacuum (`quantum evaporation'). In this concept, both scintillation photons and triplet excimers are detected using calorimeters, including calorimeters immersed in the superfluid. Kinetic excitations of the superfluid medium (rotons and phonons) are detected using quantum evaporation and subsequent atomic adsorption onto a microcalorimeter suspended in vacuum above the target helium. The energy of adsorption amplifies the phonon/roton signal before calorimetric sensing, producing a gain mechanism that can reduce the techonology's recoil energy threshold below the calorimeter energy threshold. We describe signal production and signal sensing probabilities, and estimate electron recoil discrimination. We then simulate radioactive backgrounds from gamma rays and neutrons. Dark matter - nucleon elastic scattering cross-section sensitivities are projected, demonstrating that even very small (sub-kg) target masses can probe wide regions of as-yet untested dark matter parameter space.