Publications

Sep, 2026

Conference Paper

From Commissioning to Precision Data-Taking: Resolving Operational Challenges in the Nab Detector Systems

Our understanding of the weak mixing of quarks, described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix, currently presents an anomaly. Thanks to major strides in both theory and experiment, improved precision in determinations of the first row of matrix elements has revealed disagreement with the expectation of unitarity. The Nab experiment at the Spallation Neutron Sourc…

Sep, 2026

Conference Paper

Neutron beta decay measurements with polarized neutrons and the Nab spectrometer

A polarized neutron beam and the Nab spectrometer (pNAB) at the Spallation Neutron Source will enable simultaneous measurements of the beta (A) and neutrino (B) asymmetries in free neutron decay. Combined Nab and pNAB measurements of the correlation parameters a, A, and B will determine the axial-vector to vector coupling ratio in the weak interaction with a precision of a…

Aug, 2026

Journal

Characterization of Low-energy Ionization Signals in Silicon Detectors for the Nab Experiment

The Nab (Neutron a b) experiment is designed to measure the beta-antineutrino angular correlation in free neutron 𝛽 decay with an ultimate precision goal of 0.1%, providing input for tests of Cabibbo-Kobayashi-Maskawa matrix unitarity. This measurement is performed via detection of electrons and protons in delayed coincidence using custom large-area segmented silicon detec…

Mar, 2026

Journal

First full Dalitz plot measurement in neutron 𝛽 decay using the Nab spectrometer and implications for new physics

Precision measurements of observables in neutron 𝛽 decay are used to test the standard model description of the weak interaction and search for evidence of new physics. The Nab experiment at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source was constructed to measure correlations in neutron decay by utilizing an asymmetric spectrometer and novel det…

Feb, 2026

Journal

A Novel, Steerable, Low-Energy Proton Source for Detector Characterization

We report on the conversion of the Manitoba II mass spectrometer into a versatile low-energy proton beam facility. This infrastructure is adaptable to any detector-under-test (DUT), and has proven itself effective with the characterization of silicon detectors used in subatomic beyond-the-Standard-Model (BSM) searches, namely the Nab experiment. A pencil beam of mono-energ…

Feb, 2026

ORNL Report

Fundamental Nuclear and Particle Physics At Neutron Sources

Fundamental neutron and neutrino physics at neutron sources, combining precision measurements and theory, probes new physics at energy scales well beyond the highest energies probed by the LHC and possible future high energy collider facilities. The European Spallation Source (ESS) will in the not too far future be the world’s most powerful pulsed neutron source and simult…

Aug, 2025

Journal

Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics

Processes that violate baryon number, most notably proton decay and n¯n transitions, are promising probes of physics beyond the Standard Model (BSM) needed to understand the lack of antimatter in the Universe. To interpret current and forthcoming experimental limits, theory input from nuclear matrix elements to UV complete models enters. Thus, an interplay of experiment, e…

Jul, 2025

Journal

The HIBEAM Instrument at the European Spallation Source

The European spallation source (ESS) will be the world’s brightest neutron source and will open a new intensity frontier in particle physics. The HIBEAM collaboration aims to exploit the unique potential of the ESS with a dedicated ESS instrument for particle physics which offers world-leading capability in a number of areas. The HIBEAM program includes the first search in…

Jul, 2025

Journal

The pNab experiment and the quest for ever better neutron beam polarization

The Nab and pNAB collaborations are conducting a program of studies of free neutron beta decay, with the primary goal of testing the unitarity of the Cabbibo-Kobayashi-Maskawa matrix that describes quark mixing due to the weak interaction. For this purpose, a large, novel electromagnetic spectrometer, the Nab spectrometer, has been designed, built, and placed in use to det…

Jul, 2025

Journal

Characterizing the AFP Spin Flipper for the Nab Experiment

The Nab experiment at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) aims to yield a precise measurement of the electron-neutrino correlation parameter, a, to Δaa=1×10−3 from the beta-decay of the free neutron. To achieve Nab’s precision goal, polarization of the neutron beam must be near-zero. A polarizer/analyzer combination, neutron monitors…

Jul, 2025

Journal

A Flexible Data Acquisition System Architecture for the Nab Experiment

Nov, 2024

Journal

Improved limits on 𝑛→𝑛′ transformation from the Spallation Neutron Source

Conversions between neutrons 𝑛 and dark matter candidate sterile neutrons 𝑛′ have been proposed as a mechanism for baryon number ℬ violation. In the case that there is a small mass difference Δ⁢𝑚 between the 𝑛 and the 𝑛′ states, oscillations can be induced by compensating for Δ⁢𝑚 with a magnetic field. A search for such neutron oscillations was performed at the Spallation…