Constraints on anomalous spin-spin interactions from spin-exchange collisions

Abstract: Measured and calculated cross sections for spin-exchange between alkali atoms and noble gases (specifically sodium and helium) are used to constrain anomalous spin-dependent forces between nuclei at the atomic scale ($\sim 10^{-8}~{\rm cm}$). Combined with existing stringent limits on anomalous short-range, spin-dependent couplings of the proton, the dimensionless coupling constant for a heretofore undiscovered axial vector interaction of the neutron arising from exchange of a boson of mass $\lesssim 100~{\rm eV}$ is constrained to be $g_A^n/\sqrt{4 \pi \hbar c} < 2 \times 10^{-3}$. Constraints are established for a velocity- and spin-dependent interaction $\propto \prn{\mathbf{I} \cdot \mathbf{v}} \prn{\mathbf{K} \cdot \mathbf{v}}$, where $\mathbf{I}$ and $\mathbf{K}$ are the nuclear spins of He and Na, respectively, and $\mathbf{v}$ is the relative velocity of the atoms. Constraints on torsion gravity are also considered.