Limits on possible new nucleon monopole-dipole interactions from the spin relaxation rate of polarizedHe3gas

Abstract

Various theories beyond the standard model predict new particles with masses in the sub-eV range with very weak couplings to ordinary matter. A $P$-odd and $T$-odd interaction between polarized and unpolarized nucleons proportional to $\stackrel{\ensuremath{\rightarrow}}{s}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{r}$ involving a scalar coupling ${g}_{s}$ at one vertex and a pseudoscalar coupling ${g}_{p}$ at the other vertex is one such possibility. We show that measurements of the transverse spin relaxation rate ${\ensuremath{\Gamma}}_{2}$ for polarized gas can be used to set limits on ${g}_{s}{g}_{p}$ for boson masses in the $10\ensuremath{\mu}$eV to $100$ meV range, corresponding to distances from centimeters to micrometers. We present limits from both a reanalysis of previous measurements of ${\ensuremath{\Gamma}}_{2}$ in $^{3}\mathrm{He}$ spin exchange cells and from data in a test experiment searching for a change in ${\ensuremath{\Gamma}}_{2}$ upon the motion of an unpolarized test mass. The outlook for more sensitive measurements using this technique is discussed.