Laboratory search for spin-dependent short-range force from axionlike particles using optically polarizedHe3gas

Abstract

The possible existence of short-range forces between unpolarized and polarized spin-$\frac{1}{2}$ particles has attracted the attention of physicists for decades. These forces are predicted in various theories and provide a possible new source for parity and time-reversal symmetry violation. We use an ensemble of polarized $^{3}\mathrm{He}$ gas in a cell with a $250\mathrm{\text{\ensuremath{-}}}\ensuremath{\mu}\mathrm{m}$ thick glass window to search for a force from pseudoscalar boson exchange over sub-millimeter ranges. This interaction would produce an NMR frequency shift as an unpolarized mass is moved near and far from the polarized ensemble. We report a new upper bound with a factor of 10--30 improvement on the product ${g}_{s}{g}_{p}^{n}$ of the scalar couplings to the fermions in the unpolarized mass, and the pseudoscalar coupling of the polarized neutron in the $^{3}\mathrm{He}$ nucleus for force ranges from ${10}^{\ensuremath{-}4}$ to ${10}^{\ensuremath{-}2}\text{ }\text{ }\mathrm{m}$, which corresponds to a mass range of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ to $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }\mathrm{eV}$ for the pseudoscalar boson. This represents the most sensitive search that sets a direct limit on the important ``axion window.''