Hunting Sub-gigaelectron-volt Dark Matter with Diamonds and Magnetic Microcalorimeters

Project Overview

This project is to study feasibility of a new concept for the sub-GeV dark matter (DM) detection using diamond crystals and magnetic microcalorimeters (MMCs). Diamond crystals are made of low mass carbon constituent that maximize kinetic energy of nuclear recoils from sub-GeV DM scattering due to their relatively similar masses. MMC is employed as a sensitive phonon sensor to measure athermal phonons that are produced by DM scattering in diamond crystals with 100 ns timing resolution and ~10 eV energy resolution. MMC's fast timing resolution allows high precision phonon pulse shape analysis to separate out unwanted background or noise signals in the low energy region at E < 1 keV. Especially, the low energy excess (LEE) problems have been reported in the dark matter detection community and the proposed diamond-MMC detector might be able to provide important information to understand the origins of LEE signals in DM detectors. In this project a diamond-MMC detector has been built for proof-of-concept experiments and athermal phonon collection efficiencies have been investigated for single-crystal and poly-crystal chemical-vapour-diamonds (SC and PC CVDs) as well as reference sapphire crystals are tested in the same geometries to quatify athermal phonon propagation and their collection to the MMC phonon sensors. Athermal phonon collection efficiencies and their lifetime in the diamond and sapphire crystals are successfully measured in the same geometry and experimental setup for comparison. SC CVD crystals exhibit poorer performance than the sapphire reference crystals in athermal phonon collection, while the PC CVD crystal exhibit better result than the sapphire. PC CVD with MMC phonon sensors would be feasible for sub-GeV DM detection.

Mission Impact

This work focuses on the composition and nature of dark matter, which is one of the priorities of Lawrence Livermore National Laboratory's  (LLNL) core competency in Nuclear, Chemical and Isotopic Science and Technology. The work also aligns to the advanced detector research needs of the DOE Office of Science, Office of High Energy Physics.

Publications, Presentations, and Patents

Geon-Bo Kim, Harris Kagan, and Stephen Boyd,"MAGNETO-χ: Fast Athermal Phonon Sensing with Magnetic Quantum Sensors for DM and CEvNS Detection" (Presentation, Workshop on Neutrino and Dark Matter 2022, Asheville, NC, May 2022).

Geon-Bo Kim, "Low Energy Excess in MAGNETO R&D Data" (Presentation, EXCESS Workshop 2022, Vienna, Austria, Feb 2022).