Search for macroscopic CP violating forces using a neutron EDM spectrometer

TL;DR

This study searches for macroscopic CP-violating forces mediated by axion-like particles using ultracold neutrons, setting new constraints on their coupling strength within a specific force range, significantly improving previous limits.

Contribution

It provides the first experimental constraints on axion-like particles in the 2x10^-5 m to 0.02 m range, improving existing limits by several orders of magnitude.

Findings

Established new upper limits on axion-like particle coupling constants.

Improved previous experimental constraints by 4 to 5 orders of magnitude for certain force ranges.

Excluded certain parameter spaces for CP-violating forces in the specified range.

Abstract

The search for CP violating forces between nucleons in the so-called axion window of force ranges lam between 2x10^-5 m and 0.02 m is interesting because only little experimental information is available there. Axion-like particles would induce a pseudo-magnetic field for neutrons close to bulk matter. A laboratory search investigates neutron spin precession close to a heavy mirror using ultracold neutrons in a magnetic resonance spectrometer. From the absence of a shift of the magnetic resonance we established new constraints on the coupling strength of axion-like particles in terms of the product gs x gp of scalar and pseudo-scalar dimensionless constants, as a function of the force range lam, gs x gp x lam^2 <= 2x10-21 [cm^2] (C.L.95%) for 10^-4 cm < lam < 1 cm. For 0.1 cm < lam < 1 cm previous limits are improved by 4 to 5 orders of magnitude.