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-energetic protons can be produced in a range from 25 keV to 35 keV, achieving a beam current of similar to 1 x 10-18 A. Electrostatic steering plates were constructed to direct the Gaussian-profile proton beam over a 117 mm diameter area-of-interest with full-width at half-maxima (FWHM) ranging from 0.6 mm to 1.26 mm. This work discusses the modifications and subsequent tests to confirm the beam specifications met the demands of the aforementioned detectors.

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

Precision measurements of observables in neutron beta 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 detection system to accurately reconstruct the proton momentum and electron energy for each beta decay. This work describes the detection of neutron beta-decay products in the Nab spectrometer and presents the first full Dalitz plot representation of the phase space of neutron beta decay for all electrons >100 keV. In addition, new constraints are placed on a possible excited neutron state, hypothesized to explain the disagreement between the appearance and disappearance neutron lifetime techniques.

The Nab experiment aims to extract the neutron beta decay correlation coefficients 'a' and 'b'. This will be accomplished using a 7 m tall electromagnetic spectrometer which measures electron energies and proton momenta. Detection of electrons and protons resulting from neutron beta decay will be carried out using large-area, thick, highly-segmented, single-crystal silicon detectors. These detectors and accompanying electronics will be cooled by a recirculating, gaseous helium cooling system to below 150 K with +/- 0.5 K stability. We will motivate the need for detector cooling in the Nab experiment and discuss design and performance of this cooling system.

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 detection system to accurately reconstruct the proton momentum and electron energy for each β-decay. This work describes the detection of neutron β-decay products in the Nab spectrometer and presents the first full Dalitz plot representation of the phase space of neutron β-decay for all electrons >100 keV. In addition, new constraints are placed on a possible excited neutron state, hypothesized to explain the disagreement between the appearance and disappearance neutron lifetime techniques.

The Proton Radiography (pRad) facility at the Los Alamos Neutron Science Center utilizes pulses of protons delivered by the 800 MeV linear accelerator to produce a series of radiographic images to study the dynamic behavior of materials under extreme conditions. Radiographs taken with an empty field of view, or beam pictures, are used to normalize transmission. However, because the center of the proton beam shifts between pulses, an in situ method for measuring beam position is required to normalize images for beam movement to perform absolute radiography. The beam profile monitor described here uses an array of scintillating fibers positioned in the beam path to produce light proportional to beam intensity across the beam cross section. This light is detected using fast photodiodes and a digital oscilloscope, providing a response time of several nanoseconds—suitable for measuring the 50-ns proton pulses used in pRad. The profile monitor achieves a measured position precision of 40 μm and an intensity precision of 0.7%, allowing for beam movement corrections to be applied to images, thereby improving data accuracy and image quality.

The Nab experiment at Oak Ridge National Laboratory, USA, aims to measure the beta-antineutrino angular correlation following neutron 0 decay to an anticipated precision of approximately 0.1%. The proton momentum is reconstructed through proton time-of-flight measurements, and potential systematic biases in the timing reconstruction due to detector effects must be controlled at the nanosecond level. We present a thorough and detailed semiconductor and quasiparticle transport simulation effort to provide precise pulse shapes, and report on relevant systematic effects and potential measurement schemes.

Garnet based scintillators have been shown to have high light yield with fast scintillation decay constants. The availability of high refractive index resin enables the fabrication of translucent garnet based scintillating composites; here, this study investigates optical transport improvements through reducing the refractive index difference between composite constituents. The results of this study will demonstrate radiation response characteristics of garnet based scintillating composites, support hard-radiation imaging applications, basic science and explore optical transport limitations in composite technology.

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.

We report on the measurement of the neutron radiation hardness of silicon photomultipliers (SiPMs) manufactured by Hamamatsu Corporation in Japan and SensL in Ireland. Samples from both companies were irradiated by neutrons created by a 1 GeV electron beam hitting a thin lead target at Jefferson Lab Hall A. More tests regarding the temperature dependence of the neutron radiation damage and self-annealing were performed on Hamamatsu SiPMs using a calibrated Am–Be neutron source from the Jefferson Lab Radiation Control group. As the result of irradiation both dark current and dark rate increase linearly as a function of the 1 MeV equivalent neutron fluence and a temperature dependent self-annealing effect is observed.

Hall D at Jefferson Laboratory is building its new GlueX spectrometer to study QCD gluonic excitations. The hermetic detector includes a scintillating fiber-lead barrel calorimeter where the photodetectors must operate in a high magnetic field. The silicon photomultiplier (SiPM) array manufactured by Hamamatsu Corporation was chosen for the photodetector of the BCAL. We report on the measurement of neutron radiation hardness of SiPMs at Jefferson Lab.

A 20-ton neutrino detector located near the Los Alamos Meson Physics Facility beam stop is used to search for v(e)BAR generated via neutrino oscillations from any of the three neutrino types, v(mu), v(mu)BAR, and v(e), which radiate from the beam stop. The analysis of three years of data provides limits on the oscillation modes v(mu)BAR --> v(e)BAR, v(e) --> v(e)BAR, and v(mu) --> v(e)BAR, and the lepton-number-violating decay process mu+ --> e+ + v(e)BAR + v(mu). The 90%-confidence-level limits for v(mu)BAR --> v(e)BAR oscillations are deltam2 less-than-or-equal-to 0.14 eV2 for maximal mixing, and sin(2)2theta less-than-or-equal-to 0.024 for large deltam2.

The result of a search for the neutrino oscillation mode \ensuremath{\nu}${\ifmmode\bar\else\textasciimacron\fi{}}_{\ensuremath{\mu}}$\ensuremath{\rightarrow}\ensuremath{\nu}${\ifmmode\bar\else\textasciimacron\fi{}}_{e}$ in a fine-grained tracking detector is reported. The average neutrino energy is 40 MeV and the average detector distance from the neutrino source is 26.8 m. No evidence for neutrino oscillations through this mode is observed. Limits on \ensuremath{\delta}${m}^{2}$ and ${\mathrm{sin}}^{2}$(2\ensuremath{\theta}) are presented.