Bulletin of the American Physical Society
82nd Annual Meeting of the APS Southeastern Section
Volume 60, Number 18
Wednesday–Saturday, November 18–21, 2015; Mobile, Alabama
Session B2: Unpolarized Neutron Beta Decay Studies |
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Chair: Nadia Fomin, University of Tennessee Room: Riverview Plaza Hotel Mobile Bay Ballroom II |
Thursday, November 19, 2015 11:00AM - 11:36AM |
B2.00001: The measurement of neutron beta decay observables with the Nab spectrometer Invited Speaker: Stefan Baessler Nab, an experiment that allows studying unpolarized neutron beta decay at the Spallation Neutron Source at Oak Ridge National Lab, aims to determine $a$, the neutrino-electron correlation coefficient, and $b$, the Fierz interference term, with high precision. Such measurements provide opportunities to search for evidence of extensions to the Standard Model. Nab is presently being constructed, with beam readiness planned for end of 2016. I will discuss the experiment's motivation and design, the planned modes of operation, and the performance of its components. [Preview Abstract] |
Thursday, November 19, 2015 11:36AM - 11:48AM |
B2.00002: Slow Controls for the Nab $\beta$-decay Experiment Noah Birge The Nab experiment aims to measure the free neutron $\beta$-decay parameters `a' and `b' with a relative accuracy of $10^{-3}$. The ratio between the axial-vector and vector couplings, $\lambda$, of the Standard Model will be extracted from this measured value of `a'. The experimental apparatus includes a novel 7 m long time-of-flight magnetic spectrometer and thick, large-area, highly segmented, cooled Si detectors with cooled preamplifiers at both ends of the spectrometer. For detection, the proton has to be accelerated to -30kV, and minimization of the detector backgrounds requires the spectrometer to be operated at ultra-high vacuum levels. As such, the experimental environment must be meticulously monitored and controlled to minimize systematic uncertainties. I will present requirements for the experiment and discuss plans to control and monitor the experimental environment. Additionally, since real-time data serves as a key indicator of the experimental environment, as well as accumulated statistics, a program design for online data monitoring and analysis will also be presented. [Preview Abstract] |
Thursday, November 19, 2015 11:48AM - 12:00PM |
B2.00003: Geant4 Simulation of the Nab Experiment Eric Stevens The Nab experiment at the SNS aims to measure $a$, the electron-neutrino correlation, and $b$, the Fierz interference term, in free neutron beta decay. The work reported here focuses on a precise Geant4 simulation of the Nab apparatus. Specifically, the goals of this task are to accurately model the magneto-electrostatic spectrometer, the custom segmented silicon detector response, and the overall response function of the system as a whole. Ultimately, the Geant4 code will produce fully realistic synthetic data to compare with measured data on an equal footing. Furthermore, the code has the capability to model the radioactive sources used in preliminary tests at the Ultracold Neutron Source (UCN) at the Los Alamos Neutron Science Center (LANSCE). Current results will be presented. [Preview Abstract] |
Thursday, November 19, 2015 12:00PM - 12:12PM |
B2.00004: Neutronics Calculations for the Nab Experiment Elizabeth Scott The Nab experiment measures the electron-neutrino correlation coefficient "a" and the Fierz interference term "b". Neutron beta decay measurement to a $10^{-3}$ accuracy gives an independent value of $\lambda$, the ratio of axial-vector to vector coupling constants in the nucleon. This accuracy depends on the proton momentum and electron energy with an asymmetric magnetic spectrometer and Si detector. There must be comparatively low background rates to our signal (estimated using neutron decay rate) in order to attain the necessary precision. The collimation and shielding can be modeled using MCNP (Monte Carlo N-Particle) and McStas, a Monte Carlo ray tracing program. I will present a design that optimizes the decay rate while keeping background rates sufficiently low, as well as discuss other sources of background and the corresponding attempts to reduce their rates. [Preview Abstract] |
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