The Optically Segmented Single Volume Scatter Camera (OS-SVSC) aims to image neutron sources for non-proliferation applications using the kinematic reconstruction of elastic double-scatter events. Our prototype system consists of 64 EJ-204 organic plastic scintillator bars, each measuring 5mm × 5mm × 200mm and individually wrapped in Teflon tape. The scintillator array is optically coupled to two silicon photomultiplier ArrayJ-60035 64P-PCB arrays, each comprised of 64 individual 6x6mm J-Series sensors arranged in an 8 × 8 array. We report on the design details, including component selections, mechanical design and assembly, and the electronics system. The described design leveraged existing off-the-shelf solutions to support the rapid development of a phase 1 prototype. Several valuable lessons were learned from component and system testing, including those related to the detector's mechanical structure and electrical crosstalk that we conclude originates in the commercial photodetector arrays and the associated custom breakout cards. We detail our calibration efforts, beginning with calibrations for the electronics, based on the IRS3D application-specific integrated circuits, and their associated timing resolutions, ranging from 3090ps. With electronics calibrations applied, energy and position calibrations were performed for a set of edge bars using 22 Na and 90 Sr, respectively, reporting an average resolution of 12.07±0.03mm for energy depositions between 900keVee and 1000keVee. We further demonstrate a position calibration method for the internal bars of the matrix using cosmic-ray muons as an alternative to emission sources that cannot easily access these bars, with an average measured resolution of 14.86+-0.29mm for depositions between 900keVee and 1000keVee. The coincident time resolution reported between pairs of bars measured up to 400ps from muon acquisitions. Energy and position calibration values measured with muons are consistent with those obtained using particle emission sources.

The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the $\beta$-decay asymmetry parameter, $A_0$, for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their $\beta$-decay electrons are detected with $\approx 4\pi$ acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to $b_{n}$, the Fierz interference term in the neutron $\beta$-decay rate. In this work, we determine $b_{n}$ from the energy dependence of $A_0$ using the data taken during the UCNA 2011-2013 run. In addition, we present the same type of analysis using the earlier 2010 $A$ dataset. Motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new $b_{n}$ measurement using the weighted average of our asymmetry dataset fits, to obtain $b_{n} = 0.066 \pm 0.041_{\text{stat}} \pm 0.024_{\text{syst}}$ which corresponds to a limit of $-0.012 < b_{n} < 0.144$ at the 90% confidence level.

In the UCN tau experiment, ultracold neutrons (UCN) are confined by magnetic fields and the Earth's gravitational field. Field-trapping mitigates the problem of UCN loss on material surfaces, which caused the largest correction in prior neutron experiments using material bottles. However, the neutron dynamics in field traps differ qualitatively from those in material bottles. In the latter case, neutrons bounce off material surfaces with significant diffusivity and the population quickly reaches a static spatial distribution with a density gradient induced by the gravitational potential. In contrast, the field-confined UCN-whose dynamics can be described by Hamiltonian mechanics-do not exhibit the stochastic behaviors typical of an ideal gas model as observed in material bottles. In this report, we will describe our efforts to simulate UCN trapping in the UCN tau magnetogravitational trap. We compare the simulation output to the experimental results to determine the parameters of the neutron detector and the input neutron distribution. The tuned model is then used to understand the phase-space evolution of neutrons observed in the UCN tau. experiment. We will discuss the implications of chaotic dynamics on controlling the systematic effects, such as spectral cleaning and microphonic heating, for a successful UCN lifetime experiment to reach a 0.01% level of precision.

In January, 2018, Fornal and Grinstein proposed that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in two different types of experiments. One of the possible final states discussed includes a single χ along with an e + e − pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ∼ 4π acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). We use the timing information of coincidence events to select candidate dark sector particle decays by applying a timing calibration and selecting events within a physically-forbidden timing region for conventional n → p + e - + ν̅ e decays. The summed kinetic energy ( E e + e − ) from such events is reconstructed and used to set limits, as a function of the χ mass, on the branching fraction for this decay channel.

The UCNA experiment was designed to measure the neutron β-asymmetry parameter A_0 using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for A_0 was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in 2007, 2008–2009, 2010, and 2011–2013, which ultimately culminated in a 0.67% precision result for A_0.

It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle (X) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. One of the possible final states discussed includes a single X along with an e(+)e(-) pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with similar to 4 pi acceptance using a pair of detectors that observe a volume of stored ultracold neutrons. The summed kinetic energy (E-e+(e)-) from such events is used to set limits, as a function of the X mass, on the branching fraction for this decay channel. For X masses consistent with resolving the neutron lifetime discrepancy, we exclude this as the dominant dark matter decay channel at >> 5 sigma level for 100 < E-e+(e)- < 644 keV. If the X + e(+)e(-) final state is not the only one, we set limits on its branching fraction of <10(-4) for the above E-e+(e)- range at >90% confidence level.

Background: The neutron beta-decay asymmetry parameter A(0) defines the angular correlation between the spin of the neutron and the momentum of the emitted electron. Values for A(0) permit an extraction of the ratio of the weak axial-vector to vector coupling constants, lambda g(A)/g(V), which under assumption of the conserved vector current hypothesis (g(V) = 1) determines g(A). Precise values for g(A) are important as a benchmark for lattice QCD calculations and as a test of the standard model. Purpose: The UCNA experiment, carried out at the Ultracold Neutron (UCN) source at the Los Alamos Neutron Science Center, was the first measurement of any neutron beta-decay angular correlation performed with UCN. This article reports the most precise result for A(0) obtained to date from the UCNA experiment, as a result of higher statistics and reduced key systematic uncertainties, including from the neutron polarization and the characterization of the electron detector response. Methods: UCN produced via the down scattering of moderated spallation neutrons in a solid deuterium crystal were polarized via transport through a 7 T polarizing magnet and a spin flipper, which permitted selection of either spin state. The UCN were then contained within a 3-m long cylindrical decay volume, situated along the central axis of a superconducting 1 T solenoidal spectrometer. With the neutron spins then oriented parallel or anti-parallel to the solenoidal field, an asymmetry in the numbers of emitted decay electrons detected in two electron detector packages located on both ends of the spectrometer permitted an extraction of A(0). Results: The UCNA experiment reports a new 0.67% precision result for A(0) of A(0) = -0.12054(44)(stat)(68)(syst), which yields lambda = g(A)/g(V) = -1.2783(22). Combination with the previous UCNA result and accounting for correlated systematic uncertainties produces A(0) = - 0.12015(34)(stat)(63)(syst) and lambda = g(A)/g(V) = -1.2772(20). Conclusions: This new result for A(0) and g(A)/g(V) from the UCNA experiment has provided confirmation of the shift in values for g(A)/g(V) that has emerged in the published results from more recent experiments, which are in striking disagreement with the results from older experiments. Individual systematic corrections to the asymmetries in older experiments (published prior to 2002) were >10%, whereas those in the more recent ones (published after 2002) have been of the scale of <2%. The impact of these older results on the global average will be minimized should future measurements of A(0) reach the 0.1% level of precision with central values near the most recent results.

Next Generation Experiments to Measure the Neutron Lifetime, pp. 135-143 (2014) No AccessUCNτ: Study of Lifetime Measurement in a Magneto-Gravitational TrapALEXANDER SAUNDERS, D. SALVAT, E. ADAMEK, D. BOWMAN, S. CLAYTON, C. CUDE, W. FOX, G. HOGAN, K. HICKERSON, A. T. HOLLEY, C.-Y. LIU, M. MAKELA, G. MANUS, C. MORRIS, S. PENTTILA, J. RAMSEY, S. SAWTELLE, K. SOLBERG, J. VANDERWERP, B. VORNDICK, P. WALSTROM, Z. WANG, and A. R. YOUNGALEXANDER SAUNDERSLos Alamos National Lab, Los Alamos, NM, 87545, USA, D. SALVATIndiana University, Bloomington, Indiana, USA, E. ADAMEKIndiana University, Bloomington, Indiana, USA, D. BOWMANOak Ridge National Lab, Oak Ridge, TN, USA, S. CLAYTONLos Alamos National Lab, Los Alamos, NM, USA, C. CUDEIndiana University, Bloomington, Indiana, USA, W. FOXLos Alamos National Lab, Los Alamos, NM, 87545, USA, G. HOGANLos Alamos National Lab, Los Alamos, NM, USA, K. HICKERSONCalifornia Institute of Technology, Pasadena, CA, USA, A. T. HOLLEYIndiana University, Bloomington, Indiana, USA, C.-Y. LIUIndiana University, Bloomington, Indiana, USA, M. MAKELALos Alamos National Lab, Los Alamos, NM, USA, G. MANUSIndiana University, Bloomington, Indiana, USA, C. MORRISLos Alamos National Lab, Los Alamos, NM, USA, S. PENTTILAOak Ridge National Lab, Oak Ridge, TN, USA, J. RAMSEYLos Alamos National Lab, Los Alamos, NM, USA, S. SAWTELLEIndiana University, Bloomington, Indiana, USA, K. SOLBERGIndiana University, Bloomington, Indiana, USA, J. VANDERWERPIndiana University, Bloomington, Indiana, USA, B. VORNDICKNorth Carolina State University, Raleigh, NC, USA, P. WALSTROMLos Alamos National Lab, Los Alamos, NM, USA, Z. WANGLos Alamos National Lab, Los Alamos, NM, USA, and A. R. YOUNGNorth Carolina State University, Raleigh, NC, USAhttps://doi.org/10.1142/9789814571678_0014Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: The UCNτ project is intended to develop a new measurement of the neutron lifetime using ultra-cold neutrons (UCNs) stored in a magneto-gravitational trap. In this article, we will describe the development of the experiment so far, including the trap itself, the UCN transport and monitoring system, the neutron detection methods, and the Monte Carlo simulations that have been used to model these elements. Finally, we will describe the first systematic effects that we plan to study using this apparatus. FiguresReferencesRelatedDetails Next Generation Experiments to Measure the Neutron LifetimeMetrics History PDF download

A number of inconsistant neutron lifetime measurements have been reported. The disagreement among the various measurements made with material neutron traps with ultra-cold neutrons (UCN) suggests unaccounted for systematic errors in these measurements. One potential source of error is due to the long emptying times which may be time dependent due to the UCN phase space evolution in the trap. We present a way to reduce this effect.