Improved Limit on the Permanent Electric Dipole Moment of Hg199

We report the results of a new experimental search for a permanent electric dipole moment of $^{199}mathrm{Hg}$ utilizing a stack of four vapor cells. We find $d(^{199}mathrm{Hg})=(0.49ifmmodepmelsetextpmfi{}{1.29}_{mathrm{stat}}ifmmodepmelsetextpmfi{}{0.76}_{mathrm{syst}})ifmmodetimeselsetexttimesfi{}{10}^{ensuremath{-}29}text{ }etext{ }mathrm{cm}$, and interpret this as a new upper bound, $|d(^{199}mathrm{Hg})|<3.1ifmmodetimeselsetexttimesfi{}{10}^{ensuremath{-}29}text{ }etext{ }mathrm{cm}$ (95% C.L.). This result improves our previous $^{199}mathrm{Hg}$ limit by a factor of 7, and can be used to set new constraints on $CP$ violation in physics beyond the standard model.