Bulletin of the American Physical Society
87th annual meeting of the Southeastern Section of the APS
Volume 65, Number 19
Thursday–Friday, November 5–6, 2020; Virtual
Session B01: Fundamental Symmetries - Neutron Beta Decay |
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Chair: Nadia Fomin, University of TN |
Thursday, November 5, 2020 11:00AM - 11:12AM |
B01.00001: The Nab experiment and the electric field systematic Huangxing Li The Nab collaboration will study free neutron beta decay at the Spallation Neutron Source at Oak Ridge National Lab. A neutron decays into a proton, an electron, and an anti-neutrino in this process, where the energy of the outgoing protons and electrons are collected to determine (a) the electron-antineutrino correlation co-efficient $a$ to the precision of $|\delta a /a| \le 10^{-3}$ and (b) the Fierz interference term $b$ to the precision of $|\delta b| \le 3\times10^{-3}$. This experiment will test the unitarity of the Cabibbo-Kobayashi-Maskawa Matrix, and shed light on the existence of physics beyond the Standard Model. I will talk about the motivation and design of Nab. In the second part, I will describe in detail our solution to a major systematic effect, the requirement of having a low electrical field environment in the neutron decay region. Nab will provide this with an electrode system made from materials with low work function variations ($\leq 10$ meV). [Preview Abstract] |
Thursday, November 5, 2020 11:12AM - 11:24AM |
B01.00002: Detector Characterization and Data Acquisition System Development for the “Nab” Neutron Beta Decay Experiment David Mathews The Nab neutron decay correlation experiment will measure the electron-neutrino correlation coefficient “a” and by extension test the unitarity of the CKM matrix. This coefficient will be determined through measurements of coincident protons and electrons on a pair of 127-pixel silicon detectors. In order to understand the response of the detectors to protons, the detector behavior will be tested with a 30keV proton beam at the University of Manitoba. These tests will be examining a variety of detector response features including charge sharing between pixels and the effect of radially dependent depletion voltages. In order to facilitate these tests, a new data acquisition system has been developed. This presentation will discuss the goals of the proton beam tests as well as the design of the new data acquisition system. [Preview Abstract] |
Thursday, November 5, 2020 11:24AM - 11:36AM |
B01.00003: UCNtau: Progress Towards a 0.3 s Measurement of the Neutron Lifetime Robert W. Pattie Jr. High precision measurements of properties of the neutron provide an exciting window into the structure of the standard model of particle physics. A 0.3 s measurement of the neutron lifetime, along with a similarly precise angular correlation measurement, would allow for a determination the CKM matrix element Vud from neutron observables at a comparable precision as that derived from Superallowed Fermi decays. At the Los Alamos ultracold neutron source the UCNtau collaboration is using a magneto- gravitational trap to measure the neutron’s lifetime with a precision below 0.7 s. In situ counting and the asymmetric trap design make UCNtau systematically complementary to other physical bottle and cold-neutron beam experiments. To reach an ultimate precision of <= 0.3 s several key systematic effects such as phase space evolution, uncleaned quasi-bound neutrons, and pile-up must be controlled or characterized. The status of UCNtau’s data collection and effort to characterize leading systematic effects will be presented. [Preview Abstract] |
Thursday, November 5, 2020 11:36AM - 11:48AM |
B01.00004: A Graphical User Interface-Based Framework for Ultracold Neutron Monte Carlo Simulations Mina Kemp The mean lifetime of a free neutron ($\tau_{\mathrm{n}})$ is tied to several tests of the Standard Model, such as unitarity of the CKM matrix. In order to significantly probe topics such as this, a measurement of $\tau _{\mathrm{n}}$ with a precision exceeding 0.1s is required. The goal of the UCN$\tau $ collaboration is to attain this measurement by means of a ``bottle method'' wherein ultracold neutrons (UCNs) are confined in a volume using strong magnetic field gradients. Assessing subtle systematic effects in experiments such as these depends in part on high-fidelity simulations. Standard neutron Monte Carlo codes, however, are not typically designed for simulating neutrons with energies as low as those of UCNs, which means that custom codes must be developed. This precludes the possibility of taking advantage of existing geometry or data visualization tools in a straightforward way, prompting the development of a new graphical user interface (GUI)-based framework for the UCN Monte Carlo code \textit{UCNtransport. }This framework allows for the construction/modification of geometries as well as the projection of simulation results onto these geometries. In this presentation, I will describe the creation process, physics-driven design decisions, and current capabilities of this new framework. [Preview Abstract] |
Thursday, November 5, 2020 11:48AM - 12:00PM |
B01.00005: Update on the BL2 Experiment: An In-Beam Measurement of the Neutron Lifetime Jimmy Caylor Neutron beta decay is the simplest example of semi-leptonic decay. The neutron lifetime provides an important test of unitarity and consistency of the Standard Model. The neutron lifetime is also the largest uncertainty in Big Bang Nucleosynthesis calculations of light element abundance. A precise measurement of the neutron lifetime and $\lambda$, the ratio of axial vector and vector coupling constants of the weak interaction, allow for a determination of the CKM matrix element $V_{ud}$ that is free from nuclear structure effects. A new measurement of the neutron lifetime using the in-beam method is ongoing at the NIST Center for Neutron Research. This method requires the absolute counting of decay protons in a neutron beam of precisely known flux. Improvements in the neutron and proton detection systems as well as the use of a new analysis technique should allow for a thorough investigation of major systemic effects. The experimental status, systematic tests, analysis techniques and early data will be presented. [Preview Abstract] |
Thursday, November 5, 2020 12:00PM - 12:12PM |
B01.00006: Pseudo-Data Generation for Applications to the In-Beam Neutron Lifetime Measurement Leonard Mostella The free neutron lifetime is a crucial input parameter in big bang nucleosynthesis calculations and in our understanding of the weak force, yet discrepancies in its measurement have persisted for over a decade. The two classes of experiments, the ``bottle'' and ``beam'' methods, have disagreed by over 4$\sigma $. To better understand this discrepancy, the newest generation neutron lifetime measurements are pushing for higher precision. In order to help achieve this goal, a pseudo-data set was generated for the beam lifetime experiment to benchmark current data analysis techniques as well as test new machine learning algorithms. The materials to be presented in this talk include pseudo-data generation methods, types of events created, and comparison to real data. [Preview Abstract] |
Thursday, November 5, 2020 12:12PM - 12:24PM |
B01.00007: $\beta -$decay Waveform Classification using Supervised Learning Micah Cruz Measurement of the neutron lifetime via the ``beam method'' relies on very accurately counting the decay products of neutron beta decay, namely protons. These protons are detected with silicon detectors and recorded as digitized waveforms. After detection, proton events must be correctly identified from a host of other possible events, such as cosmic rays and electrons. Supervised learning methods offer an opportunity to classify events much more quickly than traditional analysis. This relies on training a model with labeled pseudodata. This talk will feature an explanation of multiple supervised learning algorithms that were used for this study, report the accuracy of these algorithms, and discuss how they could be implemented in modern experiments. [Preview Abstract] |
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