MMC-based detection system

• Applicant: Professor Dr. Sebastian Kempf
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561595909

DELight is a new particle physics experiment to search for light dark matter (LDM) particles with masses well below 1 GeV/c2 by detecting elastic LDM scattering off a cryogenic liquid helium (LHe) target. Its low mass number, the low threshold achievable with magnetic microcalorimeters (MMCs), its intrinsic radiopurity, and the availability of several signal channels render LHe an ideal target for LDM searches. DELight can only be realized through the confluence of its six projects. Each project plays a fundamental and unique role, where this project is responsible for the magnetic microcalorimeter (MMC) based detection system. The latter will feature energy- and time-resolving large-area cryogenic microcalorimeters (LAMCALs) based on MMC technology, which will be positioned both above the liquid and submerged in the superfluid. The LAMCALs above the liquid will detect energy deposited by evaporating ⁴He atoms and photons propagating toward the liquid-vacuum interface. Those within the liquid will ideally cover the entire cell surface, detecting triplet excimer states and scintillation photons as they move towards the vessel walls. In both locations, the LAMCALs must operate at millikelvin temperatures, provide excellent energy resolution, as well as precise timing information. For this reason, each LAMCAL will consist of a thin, large-area sapphire absorber equipped with spatially distributed paramagnetic temperature sensors that are linked to superconducting athermal phonon collectors. Upon particle impact, athermal phonons are created in the absorber and propagate ballistically until absorbed by the phonon collectors. There, they are converted into quasiparticles that diffuse to the temperature sensors, depositing their energy and inducing a measurable temperature rise. This temperature change alters the sensor magnetization, which is monitored via a spiral-shaped detection coil with stripline geometry that is connected to a readout SQUID. In the first phase (Phase I), the detection system will feature 56 LAMCALs in a pancake geometry, with 37 LAMCALs positioned above the liquid and 19 submerged in the superfluid. The energy resolution of the individual LAMCALs will be 1-2 eV (FWHM), thus enabling a low energy threshold. In preparation for the second phase (Phase II) project, we will focus on exploring a double-MMC-based LAMCAL geometry for low-energy excess mitigation, developing a concept for multiplexed LAMCAL readout, and advancing the LAMCAL design to enable the detection of infrared (IR) photons.

• DFG Programme: Research Units
• Subproject of: FOR 6006: DELight: Direct Search Experiment for Light Dark Matter with Superfluid Helium
• Co-Investigator: Professor Dr. Christian Walter Dietrich Enss