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

摘要

Various theories beyond the Standard Model predict new particles with massesin the sub-eV range with very weak couplings to ordinary matter. A parity-oddinteraction 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 polarizednucleon, and $g_{V}$ and $g_{A}$ are the vector and axial vector couplings ofan interaction induced by the exchange of a new light vector boson. We report anew experimental upper bound on such possible long-range parity-oddinteractions of the neutron with nucleons and electrons from a recent searchfor parity violation in neutron spin rotation in liquid $^{4}He$. Ourconstraint on the product of vector and axial vector couplings of a possiblenew light vector boson is $g_{V}g_{A}^{n} \leq 10^{-32}$ for an interactionrange of 1m. This upper bound is more than seven orders of magnitude morestringent than the existing laboratory constraints for interaction ranges below1m, 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 performedusing neutron spin rotation measurements in heavy nuclei or through analysis ofexperiments conducted to search for nucleon-nucleon weak interactions andnuclear anapole moments.