Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session KG: Mini-Symposium on Fundamental Symmetries II |
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Chair: Nadia Fomin, University of Tennessee Room: Marquis A |
Friday, October 27, 2017 2:00PM - 2:12PM |
KG.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 2018. We discuss the experiment's motivation, expected reach, design and method, and update its overall status. [Preview Abstract] |
Friday, October 27, 2017 2:12PM - 2:24PM |
KG.00002: The Nab Spectrometer, Precision Field Mapping, and Associated Systematic Effects Jason Fry The Nab experiment will make precision measurements of $a$, the $e$-$\nu$ correlation parameter, and $b$, the Fierz interference term, in neutron beta decay, aiming to deliver an independent determination of the ratio $\lambda = G_A / G_V$ to sensitively test CKM unitarity. Nab utilizes a novel, long asymmetric spectrometer to measure the proton TOF and electron energy. We extract $a$ from the slope of the measured TOF distribution for different electron energies. A reliable relation of the measured proton TOF to $a$ requires detailed knowledge of the effective proton pathlength, which in turn imposes further requirements on the precision of the magnetic fields in the Nab spectrometer. The Nab spectrometer, magnetometry, and associated systematics will be discussed. [Preview Abstract] |
Friday, October 27, 2017 2:24PM - 2:36PM |
KG.00003: The Electric Field in the Neutron Decay Region of the Nab Experiment Huangxing Li The Nab collaboration will determine two parameters in free neutron beta decay: (a) the electron-antineutrino correlation coefficient $a$ to $|\delta a /a| \le 10^{-3}$ and (b) the Fierz interference term $b$ to $|\delta b| \le 3\times10^{-3}$. Part (a) will be done with a measurement of the two-dimensional electron energy and proton time-of-flight spectrum in the neutron beta decay. We will discuss the requirements for the electric field in the neutron decay region to achieve the desired experimental uncertainty. We will present our solution: an electrode system made from materials with low work function variations, and its characterization with a Kelvin probe. [Preview Abstract] |
Friday, October 27, 2017 2:36PM - 2:48PM |
KG.00004: Neutronics Studies for the Nab Experiment Elizabeth Scott The Nab experiment at the Spallation Neutron Source at ORNL aims to measure the neutron beta decay electron-neutrino correlation coefficient "a" and the Fierz interference term "b" with competitive precision. In Nab, the parameter "a" is extracted from the proton momentum and electron energy using an asymmetric magnetic spectrometer and two large-area highly pixelated Si detectors . To achieve $10^{-3}$ accuracy, there must be low background rates compared to our 1 kHz signal rates. The background is primarily reduced by using coincidence detection of the electron and photon from the decay. However, further reduction is still necessary. Neutron and gamma rates in the Si detectors can lead to false coincidences. The majority of this background radiation can be reduced by well designed collimation and shielding. The collimation design was done with McStas and the background shielding with MCNP6 (Monte Carlo N-Particle 6). Neutrons are absorbed by $^{6}Li$-loaded materials or borated polyethylene and gammas close to spectrometer with non magnetic materials such as lead and stainless steel. I will present the shielding design and MCNP6 results. [Preview Abstract] |
Friday, October 27, 2017 2:48PM - 3:00PM |
KG.00005: Determining a Limit on the Nab Timing Systematic Aaron Sprow Weak decay angular correlations such as that of the electron and neutrino from neutron decay can be used in precise tests of the Standard Model. The Nab experiment at the Spallation Neutron Source will determine the electron-neutrino correlation coefficient, $a$, to a fractional uncertainty of $1\times10^{-3}$ by considering the proton spectra for a fixed electron energy. Each proton energy will be determined via a time-of-flight measurement relative to the fast arrival of the coincident electron. Parametric studies show that a timing systematic of $\delta t_{\textrm{pe}}=300\,\textrm{ps}$ can saturate the Nab error budget. Presented in this talk will be a discussion of the simulation and experimental efforts designed to understand the timing systematic, and their results. [Preview Abstract] |
Friday, October 27, 2017 3:00PM - 3:12PM |
KG.00006: Programming a Detector Emulator on NI's FlexRIO Platform Michelle Gervais, Christopher Crawford, Aaron Sprow Recently digital detector emulators have been on the rise as a means to test data acquisition systems and analysis toolkits from a well understood data set. National Instruments' PXIe-7962R FPGA module and Active Technologies AT-1212 DAC module provide a customizable platform for analog output. Using a graphical programming language, we have developed a system capable of producing two time-correlated channels of analog output which sample unique amplitude spectra to mimic nuclear physics experiments. This system will be used to model the Nab experiment, in which a prompt beta decay electron is followed by a slow proton according to a defined time distribution. We will present the results of our work and discuss further development potential. [Preview Abstract] |
Friday, October 27, 2017 3:12PM - 3:24PM |
KG.00007: Overview of the Calcium-45 Beta Spectrum Measurement at Los Alamos National Laboratory Camen Royse One smoking gun of BSM physics would be the observation of a non-zero Fierz interference term, a feature in the beta spectrum produced by scalar and tensor couplings. Calcium-45 is an almost ideal candidate with which to search for a Fierz term. It is a pure beta emitter with a low endpoint of 256 keV and a simple decay scheme, with a $7/2- \rightarrow 7/2-$ g.s. to g.s. branching ratio of 99.9981(11)\%. Isospin selection rules ensure the decay is greater than about 98.5\% pure Gamow-Teller and the integrated effect of the weak magnetism over the entire spectrum is expected to be only 0.13\%. An experiment designed to precisely measure the beta spectrum of Ca-45 has been run over the past two summers at Los Alamos National Laboratory. The experiment is composed of a 4$\pi$-capture magnetic spectrometer between two segmented arrays of hexagonal silicon detectors (similar to the Nab experiment), a helium gas cooling system, front end electronics and amplifiers, and a data acquisition system which synchronizes the timing from the signals coming from both detector arrays. Data is analyzed to account for the pile-up of signals and other physical and calibration factors. An overview of the design and execution of the experiment as divided into the above topics will be presented. [Preview Abstract] |
Friday, October 27, 2017 3:24PM - 3:36PM |
KG.00008: Status of the 45Ca beta spectrum measurement at Los Alamos National Laboratory Noah Birge Although the Standard Model describes fundamental particle interactions to high precision,neutrino flavor oscillations, the observed baryon asymmetry, and complete absence of gravity from the model make it clear that there is important physics it does not describe, so called beyond the standard model (BSM). A nonzero Fierz interference term for beta decay is one candidate for BSM physics. This effect essentially manifests in the form of a distortion of the beta decay electron energy spectrum. $^{45}$Ca is a particularly appealing nucleus to attempt a measurement of the interference term, as it is a pure beta emitter. A program is in progress to perform this measurement at the Los Alamos National Lab. The 2017 run incorporates cold helium gas to cool the two detector systems. A similar system will be implemented in the Nab experiment, so this experiment also serves as an early prototype for Nab. Results of cooling tests and their effects on detector performance using a waveform analysis and preliminary energy spectra will be presented. [Preview Abstract] |
Friday, October 27, 2017 3:36PM - 3:48PM |
KG.00009: Waveform Analysis Optimization for the $^{45}$Ca Beta Decay Experiment Ryan Whitehead The $^{45}$Ca experiment is searching for a non-zero Fierz interference term, which would imply a tensor type contribution to the low-energy weak interaction, possibly signaling Beyond-the-Standard-Model (BSM) physics. Beta spectrum measurements are being performed at LANL, using the segmented, large area, Si detectors developed for the Nab and UCNB experiments. $10^{9}$ events have been recorded, with 38 of the 254 pixels instrumented, during the summers of 2016 and 2017. An important step to extracting the energy spectra is the correction of the waveform for pile-up events. A set of analysis tools has been developed to address this issue. A trapezoidal filter has been characterized and optimized for the experimental waveforms. This filter is primarily used for energy extraction, but, by adjusting certain parameters, it has been modified to identify pile-up events. The efficiency varies with the total energy of the particle and the amount deposited with each detector interaction. Preliminary results of this analysis will be presented. [Preview Abstract] |
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