New Limits on Local Lorentz Invariance in Mercury and Cesium

TL;DR

This study sets new, more stringent limits on violations of Local Lorentz Invariance using atomic spin precession measurements in mercury and cesium, improving previous bounds by a factor of four.

Contribution

It introduces a rotating table setup to enhance sensitivity and provides the first bounds on neutron and proton spin couplings to a preferred direction.

Findings

Upper bounds on dipole couplings: 19(11) nHz for Hg, 9(5) μHz for Cs

Improved bounds on Lorentz violation by a factor of four

First constraints on neutron and proton spin couplings to a preferred direction

Abstract

We report new bounds on Local Lorentz Invariance (LLI) violation in Cs and Hg. The limits are obtained through the observation of the the spin- precession frequencies of 199Hg and 133Cs atoms in their ground states as a function of the orientation of an applied magnetic field with respect to the fixed stars. We measure the amplitudes of the dipole couplings to a preferred direction in the equatorial plane to be 19(11) nHz for Hg and 9(5) microHz for Cs. The upper bounds established here improve upon previous bounds by about a factor of four. The improvement is primarily due to mounting the apparatus on a rotating table. New bounds are established on several terms in the standard model extension including the first bounds on the spin-couplings of the neutron and proton to the z direction, <7e-30 GeV and <7e-29 GeV, respectively.