Search for anomalous spin-dependent forces using stored-ion spectroscopy

Resonances in atomic ions can be used to search for new, weak, spin-dependent interactions. Upper limits on anomalous dipole-monopole and dipole-dipole couplings for the neutron and electron are determined by examining hyperfine resonances in stored ⁹Be⁺ ions. These experiments also place strict limits on anomalous weights of spinning gyroscopes.