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

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 $g_V{g}_A^n\le 10^{-32}$ 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.