Bulletin of the American Physical Society
6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Sunday–Friday, November 26–December 1 2023; Hawaii, the Big Island
Session F04: Neutron Beta Decay |
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Chair: Maninder Singh, Los Alamos National Laboratory Room: Hilton Waikoloa Village Kings 2 |
Thursday, November 30, 2023 9:00AM - 9:15AM |
F04.00001: Commissioning of SiPM detectors for the UCNA+ experiment Robert W Pattie The UCNA+ experiment hosted at the ultracold neutron source at Los Alamos National Lab plans to measure the beta-asymmetry parameter A0 to a precision of ≤0.2 %. This parameter can be used to determination λ, the ratio of the axial and vector weak coupling constants and when combined with measurements of the neutron lifetime is used to test the unitarity of the CKM quark mixing matrix and search for physics beyond the standard model. A key component of the upgrade from UCNA to UCNA+ are the SiPM-based electron detector packages at either end of the 2×2π solenoidal spectrometer. Each package is comprised of two 16-sided plastic scintillators which are readout by 128 SiPM to determine the energy and position of incident electrons. The detector packages will be installed and commissioned during the 2023 LANSCE accelerator cycle. We will present the results of offline testing at ETSU and initial commission and calibration at LANSCE. |
Thursday, November 30, 2023 9:15AM - 9:30AM |
F04.00002: Boron coated YAP:Ce scintillator as a UCN detector Martin Krivos The upcoming UCNProBe experiment at Los Alamos National Laboratory will measure the decay time of free neutrons with different systematic uncertainties than previous beam experiments. We have developed a new boron coated YAP:Ce scintillator whose properties are presented. The scintillator was tested for various scintillation properties, such as decay time, light yield, and quenching fraction. The advantage of the YAP scintillator is its high Fermi potential value, which reduces the probability for upscattering of ultracold neutrons, and thus the neutron detection efficiency can be directly measured by coincidence measurement of the 480 keV gamma radiation from neutron capture on boron. We report the scintillation studies on YAP and a preliminary UCN capture study on this boron coated scintillation and discuss the implications for the UCNProBe experiment. |
Thursday, November 30, 2023 9:30AM - 9:45AM |
F04.00003: Geant4 simulations of electron detection systematic errors for UCNA+ experiment. Rashika Gupta Significant research and development has been undertaken for the UCNA+ experiment, which is a proposed upgrade of the previous UCNA(Ultra Cold Neutron Asymmetry) experiment conducted at Los Alamos National Laboratory. The primary objective of UCNA+ would be to measure the neutron beta-asymmetry A0, which quantifies the correlation between the spin of the polarized neutron and the decay beta-particle, with a precision of less than $0.2\%$. To achieve this, UCNA+ will implement several improvements including an upgraded high-density ultracold neutron (UCN) source to enhance the statistical precision, improved detection techniques utilizing silicon photomultipliers (SiPMs), and effective reduction of electron backscattering. This talk reports on outcomes obtained through Monte Carlo simulations using Geant4 for the experimental setup of UCNA+. Specifically, we define (through Monte Carlo studies) a set of scattering measurements on the ultrathin foils used in the UCNA experiment which can directly characterize the effects of backscatter and energy loss expected for UCNA+. These measurements would be performed using conversion electron sources mounted in the UCNA spectrometer and the upgraded detector packages proposed for UCNA+. The expected accuracy of our models for scattering and the resultant uncertainties for the upgraded asymmetry experiment are explored by specifying the expected scattering effects for measurements using several conversion electron sources, thicknesses of backing foil for these sources, and various configurations for ultrathin foils used in the asymmetry measurement. Additionally, we compare different physics models employed in the simulations and investigate the influence of source positioning on the observed outcomes. |
Thursday, November 30, 2023 9:45AM - 10:00AM |
F04.00004: Data Acquisition for the Nab Detector Himal Acharya The purpose of the Nab experiment is a precise measurement of the electron-neutrino correlation factor `a' and the Fierz interference term `b' in neutron beta decay, with the goal of testing the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Two detectors are used to collect electron and proton signals from the neutron decay processes. Achieving a target uncertainty of Δa/|a| = 0.001 in `a' requires understanding the time difference between events on both detector systems with a systematic bias of 300 ps or better. A novel data acquisition system with advanced triggering capabilities based on National Instruments hardware and software resources has been developed to achieve this timing resolution. I am describing our synchronization mechanism and how we are verifying whether we meet the specification. |
Thursday, November 30, 2023 10:00AM - 10:15AM |
F04.00005: Closed Loop Helium Gas Cooling System for the Nab Experiment Love Christie The Nab experiment at the Spallation Neutron Source will use an unpolarized neutron beam to measure the electron-neutrino correlation coefficient, 'a', and the Fierz interference term, 'b.’ These neutron decay correlation parameters will be used to extract λ, the ratio of the axial-vector to vector coupling constants, to provide a measurement of the CKM matrix element Vud and test the unitarity of the CKM matrix with neutron decay that is free of nuclear corrections. The protons and electrons from neutron beta decay are measured by two highly pixelated silicon detectors. To minimize noise and optimize energy and timing resolution, the detectors are actively cooled to below 150 K. Temperature control is achieved by two closed loop helium gas systems which utilize cryocoolers. Under stable conditions, temperatures are maintained to +/- 0.5 K. This talk will focus on the implementation of the final design and performance of the detector cooling system which includes completely independent operation of designated loops for the upper and lower detector mounts in the magnetic spectrometer. |
Thursday, November 30, 2023 10:15AM - 10:30AM |
F04.00006: A Detector Testing Chamber for the Nab Experiment Michelle H Gervais The Nab experiment will study the decay electrons and protons from neutron beta decay to measure the vector to axial vector coupling ratio and search for BSM physics. It will use pixelated silicon detectors to detect these decay particles. It is important to characterize the timing and energy response of these detectors as a function of position within a pixel to understand the systematic errors. We report on the design of a detector testing chamber with a calibration source coupled to a timing detector assembly. |
Thursday, November 30, 2023 10:30AM - 10:45AM |
F04.00007: Characterizing the AFP Spin Flipper for the Nab Experiment Rebecca Godri The Nab experiment, operated at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL), aims to measure with high precision the electron-neutrino correlation parameter a and the Fierz interference term b with protons and neutrons emitted from free and unpolarized neutron β-decay. To eliminate a significant source of systematic error, the admixture from other correlation parameters with a, the neutron beam must remain unpolarized with a value less than Pn = 2 x 10-5. To characterize the polarization of the neutron beam, the Nab experiment uses a polarized 3He spin filter as an analyzer and an Adiabatic Fast Passage (AFP) neutron spin flipper to depolarize the beam. Here, we describe the efforts to characterize the efficiency of the spin flipper used in the Nab experiment. |
Thursday, November 30, 2023 10:45AM - 11:00AM |
F04.00008: Performance of the Detection System for the Nab Experiment Austin W Nelsen The decay of free neutrons enables precise studies of CKM unitarity, by measuring Vud, and searches for beyond the Standard Model physics such as weak scalar and tensor interactions. The goal of the Nab experiment, operated at the Spallation Neutron Source at Oak Ridge National Laboratory, is to measure the electron-neutrino correlation coefficient, a, and the Fierz interference term, b, to a precision δa/a = 10-3 and δb = 3×10-3, respectively, via beta decay of cold free neutrons. Nab uses two 128 channel detection systems based on silicon detectors with fast timing (10s of ns) and good energy resolution (few keV) to meet requirements for detecting and processing signals from decay electrons and protons. The system must also meet requirements of minimizing electronic and thermal noise, operation at high voltage, and temperature stability. I will present an overview of the detection systems, progress made in their commissioning, and details of their performance in the Nab experiment. |
Thursday, November 30, 2023 11:00AM - 11:15AM |
F04.00009: Unphysical magnetic monopole and implication to the phenomenology of grand unified theory. taiju tanii, Nodoka Yamanaka We show that 't Hooft-Polyakov magnetic monopoles cannot be observed. We then discuss the phenomenology of grand unified theory. |
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