New Upper Limit on the Electron's Electric Dipole Moment*

We have measured the electron's electric dipole moment (eEDM) to be $d_e = (-2.1 \pm 3.7_{\mathrm{stat}} \pm 2.5_{\mathrm{syst}}) \times 10^{-29} \; e \cdot \mathrm{cm}$.\footnote{The ACME Collaboration et al., \emph{Science} \textbf{343}, (2014) 269--272.}\textsuperscript{,}\footnote{L.~V.~Skripnikov, A.~N.~ Petrov, and A.~V.~Titov, \emph{J.~Chem.~Phys.} \textbf{139}, (2013) 221103.} This corresponds to an upper limit of $|d_e| < 8.7 \times 10^{-29} \; e \cdot \mathrm{cm}$ with 90 percent confidence, which represents an order of magnitude improvement on the previous best limit.\footnote{J.~J.~Hudson, D.~M.~Kara, I.~J.~Smallman, B.~E.~Sauer, M.~R.~Tarbutt, and E.~A.~Hinds, \emph{Nature} \textbf{473}, (2011) 493--496.} We describe our method of measuring the eEDM using a buffer gas cooled beam of thorium monoxide (ThO) and discuss our approach to finding and quantifying systematic effects.