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 Na-20 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 vertical bar(Gamma(up) - Gamma(down))vertical bar/(Gamma(up) + Gamma(down)) <3 x 10(-3). This measurement shows a possible route toward a more detailed testing of Lorentz symmetry in weak interactions.