Nab: Measurement Principles, Apparatus and Uncertainties

TL;DR

The Nab experiment aims to precisely measure neutron beta decay parameters 'a' and 'b' using a novel spectrometer, providing new insights into weak interactions and nucleon structure with high accuracy.

Contribution

It introduces a new electric/magnetic field spectrometer and detector design for neutron decay measurements, aiming for unprecedented precision and first measurement of 'b'.

Findings

Targeting 10^{-3} accuracy in (Delta a)/a

First measurement of the Fierz term 'b' in neutron decay

Independent determination of the ratio G_A/G_V

Abstract

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.