Non-ionizing Backgrounds to Light Dark Matter Searches

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Dark matter is one of the fundamental problems in our current model of the physical Universe. There is overwhelming evidence that 85% of the matter in the Universe has an unknown nature. We only see it through its gravitational imprint on large structures such as galaxies and clusters of galaxies. Because this mystery of nature is so fundamental, particle physicists, who study matter and energy, have prioritized dark matter research. There are a number of exciting new theories about dark matter with masses similar to, or even lower than, the mass of the proton. Dark matter with masses near the proton mass are interesting because the number density of dark matter and normal matter could be connected through various mechanisms that explain other outstanding questions in physics. These low-mass dark matter candidates do not deposit a significant amount of energy, so new detector technologies are required to make significant progress. The minute energy required to disturb the fragile superconducting state is of great interest because it allows us to probe for energy in nature at those minute energies, a thousandth of the energy of ionization based detectors. This low energy transition in superconductors enables better energy resolution at high energies and a lower energy threshold, exactly the characteristics required to test the hypothesis that dark matter particles may be similar in mass to the proton. Dark matter searches have systematically detected, understood, and mitigated most of the natural sources of ionizing radiation, with energies near or above the atomic scale. However, to fully exploit superconducting detectors, we now need to accomplish the same understanding of nature with non-ionizing radiation, specifically understanding any natural source of energy equivalent to an electron at 0.001 volts or above which can break cooper pairs in superconductors resulting in quasiparticles. This is an ambitious undertaking and involves bringing together different disciplines of physics and material science. I propose starting with the CUTE cryostat, being used for early science in the SuperCDMS program, and modelling the infrared environment within the cryostat. I will collaborate with NIST and Caltech on photon detection technologies that will allow both modelling and benchmarking of the infrared photon background within the CUTE cryostat. This relationship between new superconducting electronics and natural sources of radiation is a natural convergence in applied and fundamental research, which will grow as we both explore the nature of dark matter, and develop more sensitive quantum computing and sensing devices at low temperature.