Torsion Pendulum Searches for Macroscopic Spin-Interactions as a Window on New Physics

Abstract

The interactions of intrinsic particle spin offer a powerful window into important aspects of new physics, such as hidden high energy symmetries and CP-violation. This dissertation describes a new spin 20-pole torsion pendulum made with alternating high and low spin-density magnets. We operated the pendulum 4.1\,mm from a spin source and 2.0\,mm from a mass source, reaching the thermal noise level of the torsion fiber in all of our experiments. This allowed us to probe electron spin \dipdip and \mondip interactions to greater sensitivities and over shorter distances than any previously test. We found no evidence of new interactions. Our \mondip experiments set new constraints for exchange boson masses of $\sim$ 1- 500 $\mu$eV. Our \dipdip experiments set new constraints for all interaction lengths, down to 10$^{-15}$ of electromagnetic strength at infinite range.