The Nab experiment: A precision measurement of unpolarized neutron beta decay

Fry, Jason; Baessler, Stefan; Bowman, James David; Broussard, Leah; Calarco, John R.; Cianciolo, Vince; Greene, Geoffrey L.; Mueller, Paul; Penttila, Seppo; Pierce, Josh; Ramsey, John Clinton; Rykaczewski, Krzysztof

doi:10.1051/epjconf/201921904002

Title: The Nab experiment: A precision measurement of unpolarized neutron beta decay

Conference · Sun Dec 01 00:00:00 EST 2019 · EPJ Web of Conferences (Online)

DOI:https://doi.org/10.1051/epjconf/201921904002· OSTI ID:1761725

Fry, Jason ^[1]; Baessler, Stefan ^[2];

^[2];

^[2]; Calarco, John R. ^[2];

^[2]; Greene, Geoffrey L. ^[2];

^[2];

^[2]

University of Virginia
ORNL

Neutron beta decay is one of the most fundamental processes in nuclear physics and provides sensitive means to uncover the details of the weak interaction. Neutron beta decay can evaluate the ratio of axial-vector to vector coupling constants in the standard model, λ = gA/gV, through multiple decay correlations. The Nab experiment will carry out measurements of the electron-neutrino correlation parameter a with a precision of δa/a = 10^-3 and the Fierz interference term b to δb = 3 × 10^-3 in unpolarized free neutron beta decay. These results, along with a more precise measurement of the neutron lifetime, aim to deliver an independent determination of the ratio λ with a precision of δλ/λ = 0.03% that will allow an evaluation of Vud and sensitively test CKM unitarity, independent of nuclear models. Nab utilizes a novel, long asymmetric spectrometer that guides the decay electron and proton to two large area silicon detectors in order to precisely determine the electron energy and an estimation of the proton momentum from the proton time of flight. The Nab spectrometer is being commissioned at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source at Oak Ridge National Lab. We present an overview of the Nab experiment and recent updates on the spectrometer, analysis, and systematic effects.

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Research Organization:: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Nuclear Physics (NP)

DOE Contract Number:: AC05-00OR22725

OSTI ID:: 1761725

Journal Information:: EPJ Web of Conferences (Online), Vol. 219; Conference: International Workshop on Particle Physics at Neutron Sources (PPNS 2018) - Grenoble, , France - 5/24/2018 4:00:00 AM-5/26/2018 4:00:00 AM; ISSN 2100-014X

Publisher:: EDP Sciences

Country of Publication:: United States

Language:: English

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