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MON: Monday Contributed Sessions

MON 10: Standard Model and Beyond

MON 10.7: Talk

Monday, September 8, 2025, 15:45–16:00, ZHG103

Towards dark matter detection with superfluid Helium: First results from the DELight Demonstrator — •Axel Brunold, Anna Bertolini, Christian Enss, and Belina von Krosig — Kirchhoff Institute for Physics, Heidelberg University

The search for light dark matter requires innovative detection techniques capable of probing weakly interacting particles with exceptional sensitivity. One promising approach involves studying elastic scattering interactions between dark matter particles and helium atoms in the superfluid phase at millikelvin temperatures.

As part of the Direct search Experiment for Light dark matter (DELight), a pilot experiment is conducted to investigate the behavior of magnetic microcalorimeters (MMCs) submerged in liquid helium referred to as DELight Demonstrator.

In this setup, a small copper cell (300 ml) is cooled to below 50 mK within a *He/*He dilution refrigerator and filled with *He. The liquid helium level, during both filling and operation of the MMC, is monitored using an LC circuit-based level meter. At these temperatures, *He is deep in its superfluid phase, enabling a long mean free path for phonons and rotons. An MMC fabricated on a 5 mm * 5 mm silicon substrate and a resistive heater are submerged in the liquid helium. This experiment aims to explore the response of a small-scale athermal MMC (SAMCAL, small-area magnetic microcalorimeter) to phonons excited by the heater in the superfluid.

This contribution presents the DELight Demonstrator setup and recent developments in the project.

Keywords: DELight; Superfluid Helium; Dark Matter; Magnetic Microkalorimeters (MMC); Phonon detection