Search for beyond-the-Standard-Model Physics Using Optically Trapped Particles*

Models of dark matter where the particles carry a tiny electric charge (<<1 e) can arise from the presence of new forces in a hidden sector, which could mix weakly with Standard Model forces. Such stable “millicharged” dark matter particles can be searched for if they becomes bound in matter.  We use an optical trap to measure the response to an applied electric field on an object with no net integer charge, but which may contain such particles. This experiment has a fractional charge sensitivity of 10⁻⁴ electrons/ √ Hz for a wide range of millicharged particle masses, allowing exploration of uncharted regions of parameter space for such dark matter candidates.