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RESEARCH PRODUCT

Measurement of the Permanent Electric Dipole Moment of the $^{129}$Xe Atom

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We report on a measurement of the $CP$-violating permanent electric dipole moment (EDM) of the neutral $^{129}\mathrm{Xe}$ atom. Our experimental approach is based on the detection of the free precession of co-located nuclear spin-polarized $^{3}\mathrm{He}$ and $^{129}\mathrm{Xe}$ samples. The EDM measurement sensitivity benefits strongly from long spin coherence times of several hours achieved in diluted gases and homogeneous weak magnetic fields of about 400 nT. A finite EDM is indicated by a change in the precession frequency, as an electric field is periodically reversed with respect to the magnetic guiding field. Our result $(\ensuremath{-}4.7\ifmmode\pm\else\textpm\fi{}6.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}28}e\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$, is consistent with zero and is used to place a new upper limit on the $^{129}\mathrm{Xe}$ EDM: $|{d}_{\text{Xe}}|l1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}27}e\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ (95% C.L.). We also discuss the implications of this result for various $CP$-violating observables as they relate to theories of physics beyond the standard model.