A test of local Lorentz invariance with Compton scattering asymmetry

TL;DR

This study uses Compton scattering asymmetry measurements to test the invariance and isotropy of the speed of light, setting new limits on Lorentz invariance violations within the standard model extension framework.

Contribution

First to utilize Compton asymmetry measurements for testing Lorentz invariance, demonstrating the method's feasibility and establishing initial constraints.

Findings

Set a new limit of 1-n < 1.4 x 10^{-8} for the vacuum refractive index

Constrained anisotropies in the speed of light over six months

Demonstrated potential for future high-energy experiments to improve limits

Abstract

We report on a measurement of the constancy and anisotropy of the speed of light relative to the electrons in photon-electron scattering. We used the Compton scattering asymmetry measured by the new Compton polarimeter in Hall~C at Jefferson Lab to test for deviations from unity of the vacuum refractive index ($n$). For photon energies in the range of 9 - 46 MeV, we obtain a new limit of $1-n < 1.4 \times 10^{-8}$. In addition, the absence of sidereal variation over the six month period of the measurement constrains any anisotropies in the speed of light. These constitute the first study of Lorentz invariance using Compton asymmetry. Within the minimal standard model extension framework, our result yield limits on the photon and electron coefficients $\tilde{\kappa}_{0^+}^{YZ}, c_{TX}, \tilde{\kappa}_{0^+}^{ZX}$, and $c_{TY}$. Although, these limits are several orders of magnitude larger than the current best limits, they demonstrate the feasibility of using Compton asymmetry for tests of Lorentz invariance. Future parity violating electron scattering experiments at Jefferson Lab will use higher energy electrons enabling better constraints.