Speaker
Description
We are developing a time-reversal breaking test in radiative $\beta$ decay, using just the momenta of three outgoing particles. This type of time reversal is independent of nuclear spin, so explores time reversal-breaking physics unrelated to electric dipole moments (though there are model-dependent constraints at 1-loop order from null measurements of the neutron EDM). The scalar triple product of three momenta $\vec{p_1}\cdot \vec{p_2} \times \vec{p_3}$ provides a unique time-reversal odd observable, but trivially vanishes in ordinary $\beta$ decay when the three momenta sum to zero. So we need the fourth outgoing particle in radiative $\beta$ decay, considering the correlation between $\beta$, $\nu$, and $\gamma$. We add $\gamma$-ray detectors (GAGG scintillator with SiPM readout) to TRIUMF's magneto-optical trap for beta decay (TRINAT), which includes a uniform electrostatic field for efficient recoil ion detection. Explicit models produce this observable with an antisymmetric Chern-Simons term from QCD-like new interactions, interfering with the standard model vector electroweak interaction within the nucleon [S. Gardner and D. He, Phys. Rev. D 87 116012 (2013)], and among the predicted features are a quite different gamma-ray spectrum than normal bremsstrahlung. We will show initial data from the decay of 92Rb, a case without vector interactions not yet testing the explicit models.
