Electron EDM measurement in a beam of ThO: Demonstrated and planned upgrades

The permanent electric dipole moment (EDM) $d$ of a particle with spin $S$ is characterized by a linear interaction $H\propto d\,\vec{S}\cdot \vec{E}$ with an electric field $\vec{E}$. This Hamiltonian is inherently $P$- and $T$-odd, making it a powerful probe of fundamental physics. To date, no EDM of a fundamental particle has been observed, but limits placed for several particles have significantly constrained theories beyond the Standard Model in the TeV range. In 2014, the ACME collaboration set a new upper limit on the electron EDM (eEDM) of $|d|<1\times10^{-28}\, e\cdot$cm by means of a spin-precession measurement in a beam of thorium monoxide (ThO) [1]. We present our measurement scheme and demonstrated apparatus upgrades designed to suppress known systematic errors and achieve an order of magnitude greater statistical sensitivity in a next-generation measurement of the eEDM. In addition, we describe upgrades currently in development to improve our statistical sensitivity beyond next-generation levels. [1] Baron $\textit{et al.}$, Science $\textbf{343}$ (2014), 269-272