Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session KJ: Mini-Symposium on Parity Violation and Fundamental Symmetries IV |
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Chair: Daniel Salvat, University of Washington Room: Coronado |
Friday, October 30, 2015 2:00PM - 2:12PM |
KJ.00001: Nab: a precise study of unpolarized neutron beta decay Dinko Pocanic Nab is a program of measurements of unpolarized neutron decays at the Spallation Neutron Source, Oak Ridge, TN. Nab aims to determine $a$, the $e$--$\nu$ correlation with precision of $\delta a/a = 10^{-3}$, and $b$, the Fierz interference term, with uncertainty $\delta b \simeq 3\times 10^{-3}$. The set of available observables overconstrains neutron beta decay in the Standard Model (SM), opening the door to searches for evidence of possible SM extensions. Projected Nab results will lead to a new precise determination of the ratio $\lambda=G_A/G_V$, and to significant reductions in the allowed limits for both right- and left-handed scalar and tensor currents. Alternatively, Nab may detect a discrepancy from SM predictions consistent with certain realizations of supersymmetry. A long asymmetric spectrometer, optimized to achieve the required narrow proton momentum response function, is currently under construction. The apparatus is to be used in follow-up measurements (ABba experiment) of asymmetry observables $A$ and $B$ in polarized neutron decay. Nab is planned for beam readiness in 2016. We discuss the experiment's motivation, expected reach, design and method, and update its status. [Preview Abstract] |
Friday, October 30, 2015 2:12PM - 2:24PM |
KJ.00002: Performance of the Nab segmented silicon detectors: GEANT4 and data Emil Frlez The Nab Collaboration has proposed to measure neutron $\beta$-decay correlation parameters $a$ and $b$ at the Oak Ridge National Laboratory using a custom superconducting spectrometer and novel Si detectors. Two large area 2-mm thick silicon detectors, each segmented into 127 hexagonal pixels, will be used to detect the proton and electron from cold neutron decay. We present GEANT4 Monte Carlo simulations of the Si detector energy and timing responses to electrons below 1\,MeV and to 30\,keV protons with realistic simulated amplified anode waveforms. Both the data acquired with a prototype detector at Los Alamos National Laboratory with radioactive sources and the synthetic waveforms are analyzed by the same code. Energy and timing responses of the Si detectors are discussed, with the MC waveforms calibrated to the decay constants, baselines, noise, gains, and timing offsets extracted from measured data, pixel by pixel. [Preview Abstract] |
Friday, October 30, 2015 2:24PM - 2:36PM |
KJ.00003: The NPDGamma Experiment: A Measurement of the $h_{\pi}^1$ Coupling in the Hadronic Weak Interaction Jason Fry The NPDGamma Experiment was performed to measure the parity violating (PV) asymmetry in the angular distribution of gammas from polarized neutrons captured on protons at the Spallation Neutron Source in ORNL. This PV asymmetry $A_{\gamma}$ is proportional to the $\Delta I = 1$ long range weak meson coupling $h_{\pi}^1$ between nucleons in the hadronic weak interaction (HWI). Liquid para-hydrogen and aluminum production data concluded in April 2014. We will present an outline of the experiment and discuss the details of the parallel analyses methods and cuts of production data. [Preview Abstract] |
Friday, October 30, 2015 2:36PM - 2:48PM |
KJ.00004: Deep inelastic scattering investigations with kinematic variables and Monte Carlo simulations Jason Bane Physicists use scattering experiments to gain a greater understanding of a nucleon's behavior in the nucleus and how the nucleons and the underlying quark distribution are modified by the nuclear medium. In the last few years, there have been a large number of publications that focus on the possible connection between the deep inelastic EMC effect and the $x > 1$ two-nucleon correlation plateaus. We will show how using different variables may help understand the connection between these two regions as well as discussing a Monte Carlo technique to convolute the nucleon's momentum distribution with deep inelastic nucleon cross sections. [Preview Abstract] |
Friday, October 30, 2015 2:48PM - 3:00PM |
KJ.00005: Sub-1\% Electron Beam Polarimetry in Hall C at Jefferson Lab David Gaskell The electron beam polarization in experimental Hall C at Jefferson Lab has been measured with a total uncertainty of $dP/P<$0.7\% at a beam energy of $\approx$ 1~GeV. This was accomplished using two, high-precision electron beam polarimeters. The first device makes use of M\o ller scattering from atomic electrons polarized in a pure iron foil driven to magnetic saturation. The second uses polarized electron-photon (Compton) scattering from laser light stored in a low gain Fabry-Perot cavity. Data from both devices, as well as a direct comparison of the two will be shown. The polarization data that will be described were taken as part of the Q$_{weak}$ experiment in Hall C, which aimed to measure the polarization to better than 1\%. Future experiments at Jefferson Lab will require knowledge of the polarization to 0.4\% or better. In this talk, I will describe the lessons learned during the Q$_{weak}$ running and discuss prospects for improving the beam polarimetry precision to the 0.4\% level. [Preview Abstract] |
Friday, October 30, 2015 3:00PM - 3:12PM |
KJ.00006: Interior Vector Magnetic Field Monitoring via External Measurements for the SNS Neutron EDM Experiment Nima Nouri, Michael Brown, Robert Carr, Bradley Filippone, Charles Osthelder, Bradley Plaster, Simon Slutsky, Christopher Swank A prototype of a magnetic field monitoring system designed to reconstruct the vector magnetic field components (and, hence, all nine of the $\partial B_i/\partial x_j$ field gradients) within the interior measurement fiducial volume solely from external measurements is under development for the SNS neutron EDM experiment. A first-generation room-temperature prototype array has already been tested. A second-generation prototype array consisting of $12$ cryogenic-compatible fluxgate magnetometer probes will be deployed within the cold region of the experiment's $1/3$-scale cryogenic magnet testing apparatus. We will report progress towards the development of this second-generation prototype. [Preview Abstract] |
Friday, October 30, 2015 3:12PM - 3:24PM |
KJ.00007: Progress on Electrode Designs and Tests to Generate High Electric Field in Superfluid Liquid Helium-4 for the SNS nEDM Experiment Wanchun Wei, Douglas Beck, Vince Cianciolo, Steven Clayton, Christopher Crawford, Scott Currie, William Griffith, Takeyasu Ito, John Ramsey, Amy Roberts, Richardo Schmid, George Seidel, Daniel Wagner, Steven Williamson, Weijun Yao The SNS nEDM experiment is aiming to search for the neutron electric dipole moment (EDM) with ultracold neutrons (UCNs) stored in superfluid liquid helium-4 at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory, with a goal sensitivity of 3x10$^{-28}$e-cm, an improvement of two orders of magnitude over the current limit. To achieve the goal sensitivity of the EDM searches,it relies on the stable application of a 75 kV/cm electric field across the UCN storage space without breakdowns in superfluid liquid helium-4. The electrode designs and tests on various geometries and coating materials are undergoing. The high voltage tests in superfluid helium-4 are performed in a specially-designed apparatus at temperatures as low as 0.4 K and pressures between saturated vapor pressure (SVP) of liquid helium and 1 atm.These tests would help in a better understanding of the electric breakdown phenomenon in liquid helium-4. In this talk, we will present the latest progress on electrode designs and tests,and their implications of findings that affect the design of the SNS nEDM experiment. [Preview Abstract] |
Friday, October 30, 2015 3:24PM - 3:36PM |
KJ.00008: aCORN Electrostatic mirror upgrade, design and operation Md Hassan The electron-antineutrino angular correlation ($a$) in the neutron beta decay is being measured by the aCORN experiment. aCORN is aiming to measure $a$ to a relative accuracy of $1\%$ using a novel technique where electrons and protons from the neutron decay are detected in coincidence. The momenta of the particles are selected in such a way that two groups of protons are formed based on the proton time-of-flight. An electrostatic mirror reflects all protons towards the proton detector and preaccelerates them for collimation. In the last aCORN run the largest source of systematic correction was due to transverse electric fields in the mirror. For the next phase of aCORN, we upgraded the electrostatic mirror. The design and operation of the upgraded electrostatic mirror will be presented. [Preview Abstract] |
Friday, October 30, 2015 3:36PM - 3:48PM |
KJ.00009: The Design and Implementation of the aCORN Magnet Brian Collett The aCORN experiment confines the neutron decay products close to an axis using a set of collimators. The electron-antineutrino angular correlation leads to an asymmetry in the number of decay protons emerging parallel to the electron versus the number emerging anti-parallel. A measurement of the asymmetry leads to a measurement of the coefficient, ``a.'' aCORN employs a highly uniform magnetic field aligned to within 10$^{-4}$ radians of the collimator axis to limit the maximum transverse momentum of the protons. Errors in uniformity or alignment of the field lead to differences in the phase space for the two proton populations and thus to systematic errors in the value of ``a.'' The design of the magnet system, its power supplies, and the field mapping systems will be presented [Preview Abstract] |
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