Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session QJ: Neutron Physics |
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Chair: Benjamin Heacock, NIST Room: Tremont |
Thursday, October 14, 2021 11:30AM - 11:42AM |
QJ.00001: Quantum Contextuality Measurements on Mode-Entangled Neutron Beams William M Snow, David Baxter, Eric Dees, Abu Ashik Md Irfan, Steve Kuhn, Quan Minh Le Thien, Shufan Lu, Sam McKay, Gerardo Ortiz, Roger Pynn, Jiazhou Shen, Vince Vangelista, Niels Geerits, Fankang Li, Steve Parnell, Jeroem Plomp, Rob Dalgliesh We present and discuss recent measurements [1,2,3] of quantum contextuality witness values for neutron beams mode-entangled in spin, position, and energy degrees of freedom. These measurements explicitly confirm the ability of entangled slow neutron beams to evade quantum decoherence in condensed matter and may help enable precision measurements with neutron beams to avoid certain classes of systematic errors. |
Thursday, October 14, 2021 11:42AM - 11:54AM |
QJ.00002: History of Neutron Mean-Square Charge Radius Measurements Michael G Huber, Benjamin Heacock, Takuhiro FUJIIE, Katsuya Hirota, Masaaki Kitaguchi, Dmitry Pushin, Hirohiko Shimizu, Masahiro Takeda, Robert Valdillez, Yutaka Yamagata, Albert Young The neutron, being composed of charged quarks, exhibits a known spherically symmetric charge distribution. This charge distribution is quantified by the mean-square charge radius (〈rn2 〉). For the neutron 〈rn2〉 < 0 reflecting the fact that it has a slightly negative outer shell. The mean-square charge radius has been measured experimentally by its proportionality, through a series of known constants, to the neutron-electron scattering length (bne). The difficulty in measuring 〈rn2 〉 is that bne is ~1000x smaller than that of scattering off the nucleus. Prior measurements of 〈rn2〉 utilized neutron scattering from targets of noble gases or dense liquids. The Particle Data Group (PDG) considers 5 such experiments and reports an average 〈rn2〉PDG = -0.1161(22) fm2 where the error has been inflated by 30% to account for minor discrepancies. Note that the most recent measurement considered by the PDG was published in 1997. There has been renewed interest in this quantity, however, as there have been several new determinations of 〈rn2 〉. These include a χEFT approach using isotope shifts by Filin et al. (PRL 2020), an interpretation of electron scattering data by Atac et al. (Nat Com 2021), and a direct neutron measurement 〈rn2 〉 by Heacock et al. (arXiv 2021). For context on how these new determinations improve our understanding of 〈rn2〉, the speaker will discuss the current measurements making up the Particle Data Group’s average. |
Thursday, October 14, 2021 11:54AM - 12:06PM |
QJ.00003: Status of an Experiment to Measure the Parity-odd NeutronSpin Rotation in 4He Jerald A Balta The NN weak interaction is sensitive to quark-quark correlations in the nucleon and provides the means to test the Standard Model in the low energy, strongly interacting limit. Recent theoretical work [1,2] along with the measurement of the weak pion exchange component of the NN weak interaction [3] implies a large parity-odd neutron spin rotation in 4He just outside the previous measurement of dφ/dz = [+2.1 ± 8.3(stat.) ± 2.9(sys.)] × 10−7 rad/m [4]. This prediction will be updated in light of the recent measurement in the n-3He system [5]. Upgrades to the NSR apparatus enable an experimental sensitivity < [±1.0(stat.) ± 1.0(sys.)] × 10−7 rad/m [6] on the NG-C beamline at NIST. The current status of the NSR apparatus will be discussed. |
Thursday, October 14, 2021 12:06PM - 12:18PM |
QJ.00004: A Proposed Search for Time Reversal Violation in Polarized Neutron Transmission Through Polarized $^{117}$Sn Jonathan P Curole, William M Snow We describe work towards an experimental search for a P-odd and T-odd term in the polarized neutron-polarized nucleus forward scattering amplitude [1] on the 1.33 eV p-wave resonance in $^{117}$Sn, which exhibits a $10^{5}$ amplification of P-odd amplitude. $$ \frac{\Delta \sigma _{PT}}{\Delta \sigma _{P}}= \kappa (J) \frac{W}{V} $$ This formula relates the P-odd T-odd over P-odd amplitude ratio $W/V$ to the ratio $\sigma_{PT} \over \sigma_{P}$ of the P-odd T-odd to P-odd cross sections, and a spectroscopic parameter $\kappa(J)$ involving the partial neutron resonance widths in the $J=I \pm 1/2$ channels. We present a reevaluation of ($\vec{n}$,$\gamma$) angular distribution from the resonance [2] which implies a large, nonzero value for $\kappa$ that controls the T-odd sensitivity. The $I=1/2$ $^{117}$Sn nucleus can be polarized with a technique known as SABRE which we will describe. [3] |
Thursday, October 14, 2021 12:18PM - 12:30PM |
QJ.00005: Precision Measurements of the 235U(n,f) neutron-induced fission and 6Li(n,α)3He neutron reaction cross sections using the Alpha-Gamma Device. Chris Haddock The Alpha-Gamma device at the National Institute of Standards and Technology utilizes the interaction of neutrons with totally absorbing 10B targets to precisely measure the absolute flux of a monochromatic neutron beam. This absolute measurement does not require knowledge of neutron cross sections, reaction branching ratios, or the neutron beam energy. The device is being utilized in novel measurements of the 235U(n,f) neutron-induced fission reaction and 6Li(n,α)3He reaction cross sections in an effort to provide systematically independent determinations of these important quantities with comparable uncertainties. The results of recent and ongoing measurements will be presented, and planned operations will be discussed. |
Thursday, October 14, 2021 12:30PM - 12:42PM |
QJ.00006: Analysis of the Proton Quasi-Penning Trap for the BL3 Experiment Leonard D 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 primary classes of experiments, the "bottle" and "beam" methods, have disagreed by over 4σ. To better understand this discrepancy, the newest generation neutron lifetime measurements are pushing for higher precision. In order to help achieve this goal for the BL3 experiment, the next generation in-beam neutron lifetime measurement, an analysis was performed to quantify the sensitivity of the proton quasi-penning trap's effective trap length to variations in its constituent electrodes' dimensions utilizing COMSOL Multiphysics. The materials to be presented in this talk include a description of the COMSOL simulation, the method by which trap length sensitivity was determined, the allowed sensitivity tolerance to remain within the desired overall lifetime uncertainty limits, and future work to calculate corrections from these manufacturing variations. |
Thursday, October 14, 2021 12:42PM - 12:54PM |
QJ.00007: Beam Profile Corrections for BL3 Neutron Intensity Monitor Austin W Nelsen, Emily Ballantyne, Rebecca Calvert, Sarah Vickers, Chris Crawford The recent measurement of the lifetime of the free neutron using the beam method has an 8.7s (4σ) discrepancy with UCN measurements. The goal of the BL3 experiment is to improve the statistical error of this measurement and explore systematic uncertainties as an explanation for the discrepancy. A well-characterized neutron flux detector with flat response is important since the neutron flux enters linearly into the neutron lifetime. I will present a method of determining the average neutron beam position and RMS width using two rings of detectors and describe how to use this information to correct for the beam acceptance. |
Thursday, October 14, 2021 12:54PM - 1:06PM Not Participating |
QJ.00008: The current status of the UCNProBe experiment. Md T Hassan, Nicholas C Floyd, Zhaowen Tang The UCNProBe experiment aims to resolve the puzzle in the large discrepancy between neutron lifetime measured by the two distinct experimental techniques. In one method, the remaining neutrons in a UCN trap are counted after some storage time, and in the other, one of the decay particles, protons, are counted in a well-calibrated neutron beam. One possible explanation for this inconsistency is that a fraction of neutrons decays into beyond-Standard Model particles instead of protons. The UCNProBe experiment will employ a novel method to measure the proton branching ratio of neutron decay. A deuterated scintillator box will be used as a UCN storage volume and to detect electrons from the neutron decay. The current status of the UCNProBe experiment will be presented. |
Thursday, October 14, 2021 1:06PM - 1:18PM |
QJ.00009: Scintillator characterization for the UCNProBe experiment Nick Floyd, Md Taufique Hassan, Zhaowen Tang The free neutron lifetime is typically determined using one of two methods: measuring the decay products of neutrons in a well-calibrated neutron beam (beam experiment), or counting the number of surviving neutrons stored in an ultra-cold neutron (UCN) trap over time (bottle experiment). However, the lifetime results from the two methods differ by approximately four standard deviations. The UCNProBe experiment at Los Alamos aims to resolve this difference by measuring the free neutron lifetime using stored ultra-cold neutrons (UCNs) in a material trap made of deuterated scintillator. To do so, we will attempt to measure the absolute number of UCNs within the trap and the absolute number of electrons from beta decay to within 0.1 percent precision. Critical to an accurate determination of number of UCNs is a precise determination of the dead layer thickness. In this talk, we will report the characterization of the dead layer of the scintillator and the effects of heat treatment on the dead layer thickness. |
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