Light Dark Matter Detection with Hydrogen-rich Crystals and Low-Tc TES Detectors

Abstract

Direct detection of nuclear scatterings of sub-GeV Dark Matter (DM) particles favors low-Z nuclei. Hydrogen nucleus, which has a single proton, provides the best kinematic match to a light dark matter particle. The characteristic nuclear recoil energy is boosted by a factor of a few tens from those for larger nuclei used in traditional Weakly Interacting Massive Particle (WIMP) searches. Furthermore, hydrogen is optimal not only for spin-independent nuclear scattering of a sub-GeV DM, but also for spin-dependent nuclear scatterings, where large parameter space remains unconstrained yet. In this paper, we first introduce hydrogen-rich crystals, which emit two classes of signals under kinetic excitations. One class of the signals is infrared photons, which are from optically active fundamental vibrational modes of molecules and at several characteristic wavelengths. Another is acoustic phonons, and optical phonons that decay into acoustic phonons. We then discuss the technical status and future researches of low-Tc Transition-Edge Sensor (TES) detectors, which measure single infrared photons and a small flux of acoustic phonons with desirable sensitivities. With theoretical modeling to select hydrogen-rich crystals for the optimized science reach, ultra-sensitive low-Tc TES detectors for readout, and experimental prototyping of a light DM detection scheme, a detection experiment can be built for measuring the large unexplored parameter space of light DM particles.