Fundamental Neutron Physics: Current Experimental Landscape and Future Directions

The neutron is an unstable but long-lived neutral baryon, characteristics that conspire to make it a versatile laboratory for testing the Standard Model at the precision frontier. The familiar neutron plays a central role in attempts to discover new symmetries that underlie fundamental particle interactions, it is a powerful tool for understanding the baryon asymmetry of the universe and the nature of dark matter, it can be used to search for new exotic interactions, to probe the non-perturbative nature of the strong interaction, and to test foundational issues in quantum mechanics and general relativity. Its ability to facilitate such investigations means that the neutron also plays a significant role in cosmology. The experimental techniques that harness the unique properties of the neutron for such a diverse array of investigations are similarly varied. Collectively, they deal with neutrons that have energies ranging from "ultracold" (neV) to eV, but probe physics at the TeV scale. They encompass techniques from high energy particle physics, nuclear physics, optics, and condensed matter physics to achieve the extraordinary precision that determines their potential for discovering new physics. This overview will summarize aspects of the current neutron fundamental physics experimental program, highlighting the significant activity in the field by focusing on recent accomplishments and anticipated advances, and their potential impact on our understanding of the Standard Model.