Measurement of Neutron Decay Parameters-The abBA Experiment

Abstract

We are developing an experiment to measure the correlations a, A, and B, and the Fierz interference term b in neutron decay, with a precision of approximately 10^sup -4^. The experiment uses an electromagnetic spectrometer in combination with two large-area segmented silicon detectors to detect the proton and electron from the decay in coincidence, with 4π acceptance for both particles. For the neutron-polarization-dependent observables A and B, precision neutron polarimetry is achieved through the combination of a pulsed neutron beam, under construction at the SNS, and a polarized ^sup 3^He neutron polarizer. Measuring a and A in the same apparatus provides a redundant determination of λ = g^sub A^/g^sub V^. Uncertainty in λ dominates the uncertainty of CKM unitarity tests. [PUBLICATION ABSTRACT]