New Limits on Anomalous Spin-Spin Interactions

Abstract

We report the results of a new search for long-range spin-dependent interactions using a Rb−21Ne atomic comagnetometer and a rotatable electron spin source based on a SmCo5 magnet with an iron flux return. By looking for signal correlations with the orientation of the spin source we set new constraints on the product of the pseudoscalar electron and neutron couplings gepgnp/ℏc < 1.7×10−14 and on the product of their axial couplings geAgnA/ℏc < 5×10−42 to a new particle with a mass of less than about 1μ eV. Our measurements improve by about 2 orders of magnitude previous constraints on such spin-dependent interactions.