New test of time-reversal invariance in Ne19 beta decay

A new experimental upper limit on the "time-reversal" coefficient D is reported for the allowed beta decay Ne19F19+e++e. The result, expressed in terms of the relative phase angle between axial-vector (A) and vector (V) couplings, is A,V(Ne19)=180.20.4, consistent with T invariance. A nuclear-spin-polarized atomic beam of Ne19 in which either of the magnetic substates mI=12 can be selected, is allowed to terminate its flight in a cell, where the Ne19 atoms remain for approximately four seconds without substantial spin depolarization. Delayed coincidences between positrons and F19-recoil ions from decays in the cell are observed and correlated with nuclear spin to determine D. The Ne19 nuclear polarization is monitored continuously by observation of the beta-decay asymmetry.