A New Limit on Possible Long-Range Parity-odd Interactions of the Neutron from Neutron Spin Rotation in Liquid $^{4}He$

TL;DR

This paper reports a new, highly stringent experimental upper limit on long-range parity-odd interactions involving neutrons, significantly improving previous constraints and informing theories beyond the Standard Model.

Contribution

The study provides the first tight laboratory constraint on neutron-related parity-odd interactions for ranges below 1 meter, using neutron spin rotation in liquid helium.

Findings

Upper bound on $g_{V}g_{A}^{n}$ is $10^{-32}$ for 1m range.

Constraint exceeds previous limits by over seven orders of magnitude.

Results guide future searches in heavy nuclei and weak interaction experiments.

Abstract

Various theories beyond the Standard Model predict new particles with masses in the sub-eV range with very weak couplings to ordinary matter. A parity-odd interaction between polarized nucleons and unpolarized matter proportional to $g_{V}g_{A}{\vec{s}} \cdot {\vec{p}}$ is one such possibility, where ${\vec{s}}$ and ${\vec{p}}$ are the spin and the momentum of the polarized nucleon, and $g_{V}$ and $g_{A}$ are the vector and axial vector couplings of an interaction induced by the exchange of a new light vector boson. We report a new experimental upper bound on such possible long-range parity-odd interactions of the neutron with nucleons and electrons from a recent search for parity violation in neutron spin rotation in liquid $^{4}He$. Our constraint on the product of vector and axial vector couplings of a possible new light vector boson is $g_{V}g_{A}^{n} \leq 10^{-32}$ for an interaction range of 1m. This upper bound is more than seven orders of magnitude more stringent than the existing laboratory constraints for interaction ranges below 1m, corresponding to a broad range of vector boson masses above $10^{-6}$ eV. More sensitive searches for a $g_{V}g_{A}^{n}$ coupling could be performed using neutron spin rotation measurements in heavy nuclei or through analysis of experiments conducted to search for nucleon-nucleon weak interactions and nuclear anapole moments.