Improved Limits on the Spin- and Velocity-Dependent Exotic Interaction in the Micrometer Range.

Searching for exotic interactions beyond the standard model of particle physics may solve some of the current puzzles in physics. Here, the authors experimentally explore a spin- and velocity-dependent exotic interaction between the nucleons in a gold sphere and the electrons in a spin source in the micrometer range. The microfabricated spin source provides periodically varying spin density of electrons, resulting in a periodic exotic field. A cantilever glued with a gold sphere is used to measure the force acting on the gold sphere by the spin source. The spin source is driven to oscillate, and then, the imaginary component of the signal is extracted at the 10th harmonic of the oscillation frequency, which effectively separates the exotic interaction from the spurious forces commonly present in such short-range measurements. No signal of the exotic interaction is observed, then, new limits on the coupling constant are set in the interaction range below 10  μm, with f_{⊥}≤2.2×10^{-9} at 2.1  μm.