First test of Lorentz invariance in the weak decay of polarized nuclei

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A new test of Lorentz invariance in the weak interactions has been made by searching for variations in the decay rate of spin-polarized $^{20}\mathrm{Na}$ nuclei. This test is unique to Gamow-Teller transitions, as was shown in the framework of a recently developed theory that assumes a Lorentz symmetry breaking background field of tensor nature. The nuclear spins were polarized in the up and down direction, putting a limit on the amplitude of sidereal variations of the form $|({\ensuremath{\Gamma}}_{\mathrm{up}}\ensuremath{-}{\ensuremath{\Gamma}}_{\mathrm{down}})|/({\ensuremath{\Gamma}}_{\mathrm{up}}+{\ensuremath{\Gamma}}_{\mathrm{down}})<3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. This measurement shows a possible route toward a more detailed testing of Lorentz symmetry in weak interactions.