The Standard Model of particle physics is known to be incomplete. Extensions to the Standard Model, such as weak-scale supersymmetry, posit the existence of new particles and interactions that are asymmetric under time reversal (T) and nearly always predict a small yet potentially measurable electron electric dipole moment (EDM), de, in the range of 10 -27 to 10-30 e·cm. The EDM is an asymmetric charge distribution along the electron spin (S→) that is also asymmetric under T. Using the polar molecule thorium monoxide, we measured de = (-2.1 ± 3.7stat ± 2.5syst) x 10-29 e·cm. This corresponds to an upper limit of |d e| < 8.7 x 10-29 e·cm with 90%confidence, an order of magnitude improvement in sensitivity relative to the previous best limit. Our result constrains T-violating physics at the TeV energy scale.
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