Search for Millicharged Particles Using Optically Levitated Microspheres.

We report results from a search for stable particles with charge ≳10-5e in bulk matter using levitated dielectric microspheres in high vacuum. No evidence for such particles was found in a total sample of 1.4 ng, providing an upper limit on the abundance per nucleon of 2.5 × 10-14 at the 95% confidence level for the material tested. These results provide the first direct search for single particles with charge ≲0.1 e bound in macroscopic quantities of matter and demonstrate the ability to perform sensitive force measurements using optically levitated microspheres in vacuum. [ABSTRACT FROM AUTHOR]