This is the home page for the Nab and pNab collaborations. Nab is an approved and funded experiment; the Nab apparatus is currently being installed and commissioned at the Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS), Oak Ridge, Tennessee. The pNab experiment is the planned follow-up with polarized neutrons, and is currently at the Letter of Intent stage.

The Nab collaboration has undertaken to perform a precise measurement of a, the electron-neutrino correlation parameter, and b, the Fierz interference term in neutron beta decay, at 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 a, and will provide an independent measurement of λ = G_A/G_V, the ratio of axial-vector to vector coupling constants of the nucleon. We will also perform a measurement of b in neutron decay, which will provide an independent limit on the tensor weak coupling.

Following the completion of Nab measurements, pNab proposes to take over and modify the apparatus. The goal of pNab will be to measure the electron and proton asymmetries with respect to the spin of the decaying neutron, which will lead to an even more precise determination of  λ.

• The pNab experiment proposal, submitted to the FnPB PRAC on 1 July 2024.
• Nab Update and Beamtime Request, submitted to the FnPB PRAC on 1 July 2024.
• Study of neutron beta decay with the Nab experiment, accepted for publication in Eur. Phys. J Web Conf. (2024).
• "The Nab Experiment: A Precision Measurement of Unpolarized Neutron Beta Decay", published in Eur. Phys. J. Web Conf. 219, 04002 (2019)
• "Using Nab to determine correlations in unpolarized neutron decay", published in Hyperfine Interact 240, 1 (2019)
• "Detection System for Neutron β Decay Correlations in the UCNB and Nab experiments", published in Nucl. Inst. Meth. A 849, 83 (2017)
• "Characterization of large area, thick, and segmented silicon detectors for neutron β decay experiments" , published in Nucl. Inst. Meth. A 735 (2014) 408; pdf.
• Nab proposal update and funding request (27 Jan 2010).
• "Nab: measurement principles, apparatus and uncertainties" , published in Nucl. Instrum. Meth. A 611, 211-215 (2009).
• The Nab experiment proposal (9 Nov 2007).

• Slides of presentations at scientific meetings and reviews related to Nab and pNab.
• For links to early, now superseded project documents, go: here.

• Nab Wiki: The Nab collaboration Wiki pages.
• Nab CMS: content management system for ongoing work.
• Repository of internal documents for use by collaborators (through 2016).

Dinko Počanić, 29 Jul 2005.
Last updated: 1 Jul 2024.