A new device that we refer to as the spherical superconducting torsion balance has been used to search for a new force coupling mass to intrinsic spin. Our experimental approach also employs a novel spin-source geometry that allows unprecedented sensitivity in the range $100\mu \mathrm{m}<\lambda <5\mathrm{mm}$. We place new limits on the dimensionless coupling constant of such an interaction of $g_p^e{g}_s<\mathbf{(}-1.9\pm (1.3{)}_{\mathrm{stat}}\pm (1.5{)}_{\mathrm{syst}}\mathbf{)}\times {10}^{-26}$ for $\lambda >10\mathrm{mm}$ at $1\sigma$ confidence. At a range of 1 mm our most relaxed limit is $g_p^e{g}_s<1.5\times {10}^{-24}$.

• Received 20 December 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.081101