Search for an exotic parity-odd spin- and velocity-dependent interaction using a magnetic force microscope

TL;DR

This experiment used a magnetic force microscope to search for parity-odd spin- and velocity-dependent exotic interactions between polarized electrons and unpolarized nucleons, setting new limits on the coupling constant within a specific range.

Contribution

It is the first direct force measurement experiment to constrain parity-odd spin- and velocity-dependent interactions at micron scales.

Findings

No exotic signal was observed in the experiment.

The experiment sets an upper limit on the electron-nucleon coupling constant, $g_A^eg_V^N\, extless 9\times 10^{-15}$.

The method provides a new way to test physics beyond the standard model at tabletop scales.

Abstract

Exotic spin-dependent interactions may be generated by exchanging hypothetical bosons that have been proposed to solve some mysteries in physics by theories beyond the standard model of particle physics. The search for such interactions can be conducted by tabletop scale experiments using high precision measurement techniques. Here we report an experiment to explore the parity-odd interaction between moving polarized electrons and unpolarized nucleons using a magnetic force microscope. The polarized electrons are provided by the magnetic tip at the end of a silicon cantilever, and their polarizations are approximately magnetized in the plane of the magnetic coating on the tip. A periodic structure with alternative gold and silicon dioxide stripes provides unpolarized nucleons with periodic number density modulation. The exotic forces are expected to change the oscillation amplitude of the cantilever which is measured by a fiber laser interferometer. Data has been taken by scanning the tip over the nucleon source structure at constant separation, and no exotic signal related to the density modulation has been observed. Thus, the experiment sets a limit on the electron-nucleon coupling constant, $g_A^eg_V^N\leq 9\times 10^{-15}$ for 15 $\mu$m $\le \lambda \le$ 180 $\mu$m, using a direct force measurement method.