Bulletin of the American Physical Society
2019 Fall Meeting of the APS Division of Nuclear Physics
Volume 64, Number 12
Monday–Thursday, October 14–17, 2019; Crystal City, Virginia
Session RL: Mini-Symposium on Fundamental Symmetries: Theory and Experiment V |
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Chair: Christopher Crawford, University of Kentucky Room: Salon H |
Thursday, October 17, 2019 8:30AM - 8:42AM |
RL.00001: Space-based Approaches to Resolving the Neutron Lifetime Anomaly David Lawrence, Jack Wilson, Vincent Eke, Jacob Kegerreis, Patrick Peplowski Free neutrons decay via the weak interaction with a mean lifetime of around 882 s. Knowledge of this lifetime is important as it provides constraints on the unitarity of the CKM matrix and is a key parameter for studies of Big Bang nucleosynthesis. Two classes of experiments have successfully made measurements of neutron lifetime: the `Beam' class involve measuring the activation of cold neutron beams and the `Bottle' class uses storage (material, magnetic and/or gravitational) to trap neutrons and measure the rate of decay during storage. However, there currently exists a 4-sigma disagreement between the `beam' and `bottle' measurements. Here, we discuss new techniques to measure the neutron lifetime using space-based neutron spectroscopy. We will present several possible designs for space-based experiments suitable for use at the Moon or terrestrial planets. These instruments are based on detectors previously flown on NASA planetary science missions including Lunar Prospector and MESSENGER. We will discuss the scale of expected systematics and place constraints on the mass, power and orbital characteristics required to make a measurement of neutron lifetime with sufficiently small uncertainty to help resolve the current discrepancy. [Preview Abstract] |
Thursday, October 17, 2019 8:42AM - 8:54AM |
RL.00002: An experiment to measure the Proton Branching Ratio in Neutron Beta Decay (UCNProBe) Md Hassan, Zhaowen Tang, Chris Cude-Woods, Steven Clyton, Takeyasu Ito, Bo Jhonson, Mark Makela, Chris Moris, Chris O'Shaughnessy, Andy Saunders The free neutron decays into an electron, proton, and antineutrino with a characteristic lifetime with a 100{\%} branching ratio according to the Standard Model. The neutron lifetime has been measured primarily in two methods: the beam method and the ultracold neutron (UCN) bottle method. The lifetime measured in these two methods differs by about five standard deviations. One potential explanation for this discrepancy is that some fraction of neutron decays produce undiscovered decay particles instead of protons. The UCNProBe experiment aims to resolve this inconsistency by implying a novel technique to determine the neutron decay branching ratio using a deuterated scintillator box as a UCN storage volume to detect electrons from the beta decay. An overview and update of the UCNProBe experiment will be presented. [Preview Abstract] |
Thursday, October 17, 2019 8:54AM - 9:06AM |
RL.00003: Precision Measurement of Cold Neutron Flux using Alpha-Gamma Evan Adamek The Alpha-Gamma device at NIST utilizes the interaction of neutrons with a totally absorbing $^{10}$B target to precisely measure the flux of a monochromatic neutron beam. This measurement provides a calibration of the $^{6}$Li(n,$\alpha$)$^{3}$H based flux monitor used in the NIST neutron lifetime experiment to better than 0.1% and has been utilized in novel measurements of the $^{6}$Li neutron cross section. Measurement of other standard neutron cross sections and a recalibration of the United States’ national neutron source are underway. The results of recent measurements will be presented, and planned operations using Alpha-Gamma will be discussed. [Preview Abstract] |
Thursday, October 17, 2019 9:06AM - 9:18AM |
RL.00004: Absolute Proton Detection Efficiency Determination in ``Beam'' Experiments Grant Riley This talk~introduces~a new proposed method to measure proton detector efficiency for use in ``beam'' determinations of the free neutron lifetime.~ There is currently a 4-sigma disagreement between the ``beam'' and ``storage'' methods of measuring the lifetime of the neutron.~ A possible reason for this is a systematic uncertainty that is not properly accounted for in one or both types of experiments. Absolute proton counting is an essential to the ``beam'' experimental approach.~ The absolute detector efficiency is not currently known for existing experiments and could be a source of a hidden systematic error. This proposed calibration technique can also be extended to new, large area particle detectors designed for future experiments. [Preview Abstract] |
Thursday, October 17, 2019 9:18AM - 9:30AM |
RL.00005: Magnetic Field Characterization of the UCN$\tau$ Magneto-gravitational Ultracold Neutron Trap Adam Holley The UCN$\tau$ experiment employs a large-volume magneto-gravitational trap to measure the free neutron lifetime by counting surviving ultracold neutrons (UCN) following storage in a combined magnetic and gravitational potential. In this ``bottle'' approach, loss of UCN from any non-$\beta$-decay process produces a systematic error. Magnetic field gradients generated by, for example, an array of permanent magnets can be used to confine polarized UCN, eliminating wall interactions that lead to such losses, the dominant systematic effect in non-magnetic (material) bottles. What remains is a small residual systematic effect associated with the dynamics of UCN spin in the trap. Assessing both the effectiveness of the trapping potential at preventing wall collisions, as well as spin dynamics, requires measuring the magnetic field with $\sim$mm spatial precision near the surface of the trap. We have constructed an automated magnetic mapper capable of performing \textit{in situ} magnetic field maps of the UCN$\tau$ Halbach array with high spatial precision, and are engaged in an ongoing mapping campaign to characterize the UCN$\tau$ trap. We will describe this instrument, present a first set of detailed scans, and discuss implications for magnetic field related systematic effects. [Preview Abstract] |
Thursday, October 17, 2019 9:30AM - 9:42AM |
RL.00006: Measuring Systematic Effects in the UCN$\tau$ Experiment Francisco Gonzalez The UCN$\tau$ experiment at Los Alamos National Laboratory measures the neutron lifetime by storing ultracold neutrons (UCN) in a magnetogravitational trap for variable holding times. Loss mechanisms besides $\beta$-decay add systematic uncertainties by potentially removing UCN before detection. Magnetic field anomalies can enhance UCN depolarization rates. Field mapping and in-situ detection help place limits on this effect. Before storage, UCN with energies above the trapping potential are removed, but over-threshold UCN could escape due to heating or insufficient cleaning. In-situ detection at various heights and an improved cleaner detector monitor high-energy UCN, constraining these losses. Detection and spectral cleaning efficiency couple to UCN phase-space distribution. Comparing UCN arrival times quantifies phase-space evolution. A buffer volume installed between the UCN source and trap has improved characterization of the UCN spectrum and reduced the effect of the beam structure on normalization. Alongside these improvements, Monte Carlo simulations of UCN trajectories give insight needed to understand and minimize loss mechanisms. We will present work done to constrain these systematic effects as part of an effort to reduce UCN$\tau$'s total uncertainty to about 0.25s. [Preview Abstract] |
Thursday, October 17, 2019 9:42AM - 9:54AM |
RL.00007: ABSTRACT WITHDRAWN |
Thursday, October 17, 2019 9:54AM - 10:06AM |
RL.00008: Preliminary Design of the Magnet System for the LANL nEDM Experiment Jared Brewington Permanent electric dipole moments represent a prospective avenue for the discovery of beyond standard model physics. The advent of experimental techniques using stored ultracold neutrons (UCNs) has placed the neutron electric dipole moment (nEDM) at the forefront of EDM searches. The current experimental upper limit for the nEDM is $d_n < 3\times10^{-26}$ e-cm (90\% CL). The neutron EDM search to be conducted at Los Alamos National Laboratory (LANL) aims to advance the experimental measurement of the nEDM by an order of magnitude. Achieving the goal sensitivity of $3\times10^{-27}$ e-cm requires a highly uniform $B_0$ holding field as well as efficient transport of UCN polarization from the neutron source into the storage volume. This talk will discuss the design techniques and preliminary design of the $B_0$ coil and the spin transport coil system for the LANL-nEDM experiment. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Award Number DE-SC0014622, the NSF under Award Number PHY-1828568, and by the LANL LDRD program. [Preview Abstract] |
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