Test of Lorentz invariance with spin precession of ultracold neutrons

TL;DR

This study tests Lorentz invariance using ultracold neutrons and mercury atoms, setting new limits on cosmic anisotropy and neutron gravitational dipole moment through spin precession measurements.

Contribution

It provides the first experimental limit on Lorentz invariance violation for free neutrons using ultracold neutron spin precession.

Findings

No daily variation in spin precession ratio detected

Sets an upper limit on Lorentz invariance violating field $b_{ot} < 2 imes 10^{-20} eV$

Establishes a limit on the neutron's gravitational dipole moment $|g_n| < 3 imes 10^{-4} eV/c^2$

Abstract

A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and $^{199}$Hg atoms is reported. %57 No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field $b_{\bot} < 2 \times 10^{-20} {\rm eV}$ (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron $|g_n| < 0.3 $eV/$c^2$ m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit $|g_n| < 3 \times 10^{-4} $eV/$c^2 $m.