Constraining short-range spin-dependent forces with polarized ${}^3$He

We have searched for a short-range spin-dependent interaction using the spin relaxation of hyperpolarized ${}^3$He. Such a new interaction would be mediated by a hypothetical light scalar boson with \CP-violating couplings to the neutron. The walls of the ${}^3$He cell would generate a pseudomagnetic field and induce an extra depolarization channel. We did not see any anomalous spin relaxation and we report the limit for interaction ranges $\lambda$ between $1$ and $100\mu \mathrm{m}$: $g_sg_p \lambda ^2 \leq 2.6\times 10^{-28}~${\mathrm{m}}^2$, ( 95~%, $\mathrm{C}\mathrm{.}\mathrm{L}\mathrm{.}$)$,where$g_s$($g_p$) are the (pseudo)scalar coupling constant, improving the previous best limit by 1 order of magnitude.