Limiting CP violation through a search for a permanent electric dipole moment of mercury 199 atoms

Abstract

The measurement of a nonzero permanent electric dipole moment (EDM) on an atom or particle would reveal a new source of CP violation beyond the Standard Model. The first measurement of the 199Hg EDM using a UV laser to optically pump and probe a stack of two 199 Hg vapor cells has been completed yielding the result, d( 199Hg) = -(1.06 +/- 0.49stat. +/- 0.40 syst.) x 10-28 e cm. This result can be interpreted as an upper bound of |d( 199Hg)| < 2.1 x 10-28 e cm (95% confidence level), which when combined with theoretical calculations, can be used to place stringent bounds on a variety of CP violating parameters, including the EDM of the proton, theta QCD, and CP-violating angles originating from supersymmetric theories. An improved version of the experiment using a stack of four 199Hg vapor cells has been built where the two additional cells act as magnetometers and help to improve both the statistical and systematic uncertainties. The new apparatus has been able to improve the statistical sensitivity per unit time by a factor of three, and the magnetometer cells have helped uncover many instances of false signals.