Nab: Measurement principles, apparatus and uncertainties

The Nab collaboration will perform a precise measurement of a, the electron-neutrino correlation parameter, and b, the Fierz interference term in neutron beta decay, in the Fundamental Neutron Physics Beamline at the SNS, using a novel electric/magnetic field spectrometer and detector design. The experiment is aiming at the 10(-3) accuracy level in Delta a/a, and will provide an independent measurement of lambda = G(A)/G(V), the ratio of axial-vector to vector coupling constants of the nucleon. Nab also plans to perform the first ever measurement of b in neutron decay, which will provide an independent limit on the tensor weak coupling. (C) 2009 Elsevier B.V. All rights reserved.