Home page of the Nab and
pNab experiments at the SNS
This is the home page for the Nab
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
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 =
GA/GV, 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
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.
Active collaborating institutions on Nab and pNab
- Arizona State University
- Technische Hochschule Karlsruhe
- Eastern Kentucky University
- University of Kentucky
- Western Kentucky University
- Los Alamos National Laboratory
- University of Manitoba
- Universidad Autonoma de Mexico
- University of Michigan
- North Carolina State University
- Oak Ridge National Laboratory
- University of South Carolina
- University of Tennessee, Chattanooga
- University of Tennessee, Knoxville
- University of Virginia
- University of Winnipeg
Documentation and Publications
- Draft of the pNab Letter of Intent, as
of December 2020.
Nab Experiment: A Precision Measurement of Unpolarized Neutron Beta
published in Eur. Phys. J. Web Conf. 219, 04002 (2019)
Nab to determine correlations in unpolarized neutron decay"
published in Hyperfine Interact 240, 1 (2019)
System for Neutron β Decay Correlations in the UCNB and Nab experiments"
published in Nucl. Inst. Meth. A 849, 83 (2017)
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).
measurement principles, apparatus and uncertainties"
, published in Nucl. Instrum. Meth. A 611,
- The Nab experiment
proposal (9 Nov 2007).
presentations relating to
FnPB PRAC meetings, DoE reviews, as well
as at workshops and conferences. Some photos of equipment in
development are also given.
Links to early, now superseded documents
- The abBA experiment
proposal (9 Nov 2007); superseded by the pNab LoI .
- The PANDA
experiment proposal (9 Nov 2007); superseded by the pNab LoI.
- The abBA Letter of Intent (24 Aug
2005); superseded by the abBA proposal and the pNab LoI.
- The Nab Letter of Intent, submitted to
the SNS Program Advisory Committee on 29 July 2005; superseded in
2007 by the Nab proposal.
Useful internal links for Nab collaborators
- 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: 8 Jan 2021.
This work has been supported by the US National Science
Foundation, the US Department of Energy, University of Virginia,
Arizona State University, and from other sources.