Time-reversal invariance in the β-decays of A = 8 nuclei

Abstract

We examine time reversal invariance in the beta-decays of 8B(2+) and 8Li(2+) to 8Be(2+) in detail, with particular attention to final state interactions of the two alpha particles from the decay of 8Be, and of the electron (positron) with the daughter nucleus. A R-matrix formulation is used, with the initial state described by a shell model. The R-matrix parameters are obtained by fitting the alpha-\alpha scattering phase shifts and allowed beta-decay rates. Because the nuclear final state interaction effects on the time reversal test come from second forbidden beta-decays, they are small and can be minimized by a suitable choice of kinematic conditions. The e(+/-)-nucleus Coulomb interaction induced T-violation effects depend on the first forbidden operators.