Test of the rotational invariance of the weak interaction

Abstract

We consider the possibility that the weak interaction might recognize a preferred direction in space. We report a search for anisotropy in the $\ensuremath{\beta}$ decay of unpolarized $^{90}\mathrm{Y}$ nuclei. Our result may be expressed in terms of an expansion of the angular distribution of the decay electron: $\ensuremath{\Gamma}(\ensuremath{\theta})\ensuremath{\propto}1+{\ensuremath{\epsilon}}_{1}cos\ensuremath{\theta}+{\ensuremath{\epsilon}}_{2}{cos}^{2}\ensuremath{\theta}+\ensuremath{\cdots}$, where $\ensuremath{\theta}$ is the angle between the direction of emission of the electron and any supposed asymmetry axis. We find for any axis that $|{\ensuremath{\epsilon}}_{1}|<{10}^{\ensuremath{-}6.8}$ and $|{\ensuremath{\epsilon}}_{2}|<{10}^{\ensuremath{-}5.7}$ (90% confidence limits).