A Torsion-Balance Search for Axion-Like Particles

Axion-like particles can mediate macroscopic parity and time-reversal symmetry violating forces. We will present a search for such a force between polarized electrons and unpolarized atoms using a novel torsion pendulum operating in the unshielded magnetic field of an electromagnet. Laboratory bounds on this force were improved by more than 10 orders of magnitude for pseudoscalars heavier than $1\,\mathrm{meV}$, and constraints on this force were established over a broad range of astrophysically interesting masses from $10\,\mu\mathrm{eV}$ to $10\,\mathrm{meV}$. Plans for a next generation of this experiment will be discussed.