Development of a test of time reversal invariance in neon-19 beta decay

This work reports on the development of a new test of time reversal invariance in the beta decay /sp [19]Ne/to F/sp-4 + e⁺ + ν_e. The measurement involves the detection of the positron and the left over recoil ion from the decay, to determine the time reversal odd angular correlation D Jċ [[/ p/sb e × / p/sb/nu]/over[E/sb e/ E/sb /nu]], where D measures the strength of the T-violating term in the decay amplitude, and the vector J, is the initial /sp [19]Ne polarization. /sp [19]Ne is produced for the experiment using a (p,n) reaction on a SF/sb 6 gas target, and polarization is achieved using a Stern-Gerlach magnet. The radioactive gas species is collected in a 14 second holding time cell at the end of the Stern-Gerlach apparatus. A new detection system has been designed and built for this experiment. The detector cell is in the shape of a cube, with the four side faces perpendicular to the /sp [19]Ne spin axis being sensitive to both recoil ions and positrons. Most of the decays occur in the central equipotential region surrounded by a fine grid in the cell. Recoil ions, after crossing through the gridded region, are accelerated into the front faces of large (5 cm x 5 cm) microchannel plates (MCPs), whose electron showers are then detected by underlying position sensitive silicon strip detectors which act as the readout device for the MCPs. The positrons in the decay are also detected using the silicon strip detectors. The geometric sensitivity to the T-odd correlation has been estimated through Monte-Carlo studies to be G/sb D/ /approx.26. The position sensitivity of the silicon detectors will be used to study possible position dependent ion detection efficiency variations, which could lead to a spurious non-zero signal for the T-odd term. Assuming a factor of two increase in the observed ion detection efficiency, and a 30 μA cyclotron beam, the estimated runtime to a statistical precision on D of σ/sb D=1 × 10^-4 is 744 hours (assuming a washout factor of 0.86), close to the final state effect which enters at D ≈ 1.4 × 10/sp [- 4].