Production of Dark Sector Particles via Resonant Positron Annihilation on Atomic Electrons

Resonant positron annihilation on atomic electrons provides a powerful method to search for light new particles coupled to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msup><a:mrow><a:mi>e</a:mi></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup><a:msup><a:mrow><a:mi>e</a:mi></a:mrow><a:mrow><a:mo>−</a:mo></a:mrow></a:msup></a:mrow></a:math>. Reliable estimates of production rates require a detailed characterization of electron momentum distributions. We describe a general method that harnesses the target material Compton profile to properly include electron velocity effects in resonant annihilation cross sections. We additionally find that high-<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>Z</c:mi></c:math> atoms can efficiently act as particle physics accelerators, providing a density of relativistic electrons that allows one to extend by several times the experimental mass reach. Published by the American Physical Society 2024