Testing isotropy of the universe using the Ramsey resonance technique on ultracold neutron spins

TL;DR

This paper reports a sensitive test of the universe's isotropy using ultracold neutron spins and the Ramsey resonance technique, setting stringent limits on Lorentz invariance violations.

Contribution

It presents the first clock-comparison experiment with free neutrons to test cosmic isotropy and Lorentz invariance using ultracold neutrons and Ramsey resonance.

Findings

No daily variation in neutron precession frequency detected

Sets new stringent limits on Lorentz invariance violations

Demonstrates the effectiveness of Ramsey resonance in fundamental symmetry tests

Abstract

Physics at the Planck scale could be revealed by looking for tiny violations of fundamental symmetries in low energy experiments. In 2008, a sensitive test of the isotropy of the Universe using has been performed with stored ultracold neutrons (UCN), this is the first clock-comparison experiment performed with free neutrons. During several days we monitored the Larmor frequency of neutron spins in a weak magnetic field using the Ramsey resonance technique. An non-zero cosmic axial field, violating rotational symmetry, would induce a daily variation of the precession frequency. Our null result constitutes one of the most stringent tests of Lorentz invariance to date.