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

A new test of Lorentz invariance in the weak interactions has been made by searching for variations in the decay rate of spin-polarized Na20 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 |(Γ_up-Γ_down)|/(Γ_up+Γ_down)<3×10^-3. This measurement shows a possible route toward a more detailed testing of Lorentz symmetry in weak interactions.