Publications

Showing 22 results for Author: John C. Ramsey

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  • 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…

  • 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

    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

    Measurement of the free neutron lifetime in a magneto-gravitational trap with in situ detection

    Here we publish three years of data from the UCNτ experiment performed at the Los Alamos Ultracold Neutron Facility at the Los Alamos Neutron Science Center. These data are in addition to our previously published data. Our goals in this paper are to better understand and quantify systematic uncertainties and to improve the lifetime statistical precision. We previously repo…

  • 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…

  • Nov, 2024

    Journal

    A novel silicon photomultiplier readout architecture for low-light applications

    In this article we describe the photon detection readout electronics for the nEDM@SNS experiment. The chosen "photon counting" architecture, which utilizes high-efficiency silicon photomultipliers (SiPMs) and is appropriate for low-light applications, allows the use of a relatively high SiPM operating voltage. This maximizes photon detection efficiency and minimizes gain/e…

  • Oct, 2024

    Conference Paper

    Study of neutron beta decay with the Nab experiment

    The current three sigma tension in the unitarity test of the Cabbibo-Kobayashi-Maskawa (CKM) matrix is a notable problem with the Standard Model of elementary particle physics. A long-standing goal of the study of free neutron beta decay is to better determine the CKM element Vud through measurements of the neutron lifetime and a decay correlation parameter. The Nab collab…

  • Sep, 2024

    Journal

    Fill and dump measurement of the neutron lifetime using an asymmetric magneto-gravitational trap

    The past two decades have yielded several new measurements and reanalysis of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the most precise lifetime measured in neutron storage experiments. Measurements using diffe…

  • Nov, 2023

    Journal

    A new cryogenic apparatus to search for the neutron electric dipole moment

    A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). This apparatus uses superfluid 4He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experime…

  • Nov, 2023

    Journal

    Improved Neutron Lifetime Measurement with UCNτ

    We report an improved measurement of the free neutron lifetime τn using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38×106 surviving ultracold neutrons (UCNs) after storing in UCNτ’s magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τn from three blinded, independent analyses by bot…

  • Nov, 2023

    Journal

    Effect of an electric field on liquid helium scintillation produced by fast electrons

    The dependence on applied electric field (0–40 kV/cm) of the scintillation light produced by fast electrons and α particles stopped in liquid helium in the temperature range of 0.44 K to 3.12 K is reported. For both types of particles, the reduction in the intensity of the scintillation signal due to the applied field exhibits an apparent temperature dependence. Using an a…

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