Carlos Blanco, Ph.D. Assistant Professor, Department of Physics, Pennsylvania State University

Directional Molecular Crystals for Low-Background Sub-GeV Dark Matter Detection

Abstract

This program seeks to discover materials purpose-made to detect dark matter directly, by implementing a molecular design loop from first-principles theory to laboratory validation. Dark matter comprises 85% of all the matter in the universe, yet uncovering its nature remains a central problem in physics and cosmology. The latest experimental and theoretical developments point to dark matter particles lighter than a hydrogen atom, whose faint signals are drowned out by currently irreducible noise in the most sensitive existing experiments. Our group discovered that crystals built from organic (carbon-based) molecules offer a way to see through this noise in order to probe these light dark matter candidates. As dark matter arrives on Earth predominantly from the direction of the constellation Cygnus, it collides with a molecular crystal along the orientation of this dark matter wind. Our detection concept takes advantage of the fact that the aligned molecules in such a crystal convert the impact into a scintillating flash of light more readily for some arrival directions than for others. The rate of scintillation rises and falls in step with Earth's rotation relative to the stars, a smoking-gun signal that cuts through the noise. Guided by our quantum theory of how dark matter excites these crystals, we will use machine learning to design molecules with the strongest and most direction-sensitive response, and validate the leading candidates with polarized-light spectroscopy in our laboratory at Penn State. Our team pioneered this approach, from the first calculations of dark matter scattering in molecules to the first generative machine-learning model for detector molecules, and our experimental collaborators at MIT and Fermilab are already building a first prototype from the crystal that our theory identified. This work will explore the vast space of possible molecules to identify optimal candidates. We will establish molecular crystals as a directional, low-background frontier in the search for dark matter while advancing molecular design tools with applications from quantum sensing to solar energy harvesting.

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