Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E13: Fundamental Symmetries ILive
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Sponsoring Units: DNP Chair: Prajwal MohanMurthy, University of Chicago |
Saturday, April 17, 2021 3:45PM - 3:57PM Live |
E13.00001: QCD Analysis of $\Delta S=0$ Hadronic Parity Violation Girish Muralidhara, Susan Gardner For many years the primary goal of hadronic parity nonconservation studies in nucleons and nuclei has been the identification of the isovector weak force, which has been expected to be dominated by long-range pion exchange. Recent theoretical and experimental developments prompt a broader view, suggesting that isoscalar and isotensor weak forces also play important phenomenological roles. Thus we revisit the QCD analysis of the effective weak Hamiltonian at hadronic energy scales for strangeness-nonchanging ($\Delta S=0$) hadronic processes. Performing a leading-order renormalization group analysis in QCD from the weak to hadronic energy scales, we derive the pertinent effective Hamiltonian for hadronic parity violation, including the effects of both neutral and charged weak currents at the electroweak scale. We show that the additional four-quark operators that enter at low energy scales from QCD operator mixing effects form a closed set and that they result in a 12$\times$12 anomalous dimension matrix. Employing the factorization {\it Ansatz} and using recent assessments of the quark axial charges of the nucleon in lattice QCD, we make concrete estimates of the weak meson-nucleon couplings for comparison with existing work. [Preview Abstract] |
Saturday, April 17, 2021 3:57PM - 4:09PM Live |
E13.00002: Proof of anticommutation between exchange and charge conjugation Daniel Miller We prove anticommutation between the exchange and charge conjugation of Lorenz invariant bispinors by raising the Lorenz symmetry to $SO(3N,N)$ and lowering it back to $SO(3,1)$. This finding contradicts one of the foundations of the spin--statistics theorem and the exclusion principle for antimatter. An experimental confirmation of the present theory will open up a path to solve the paradox of the matter--antimatter asymmetry of the universe in a quantum electrodynamics framework. The antimatter universe will be unstable owing to the lack of degeneracy pressure. [Preview Abstract] |
Saturday, April 17, 2021 4:09PM - 4:21PM Live |
E13.00003: Computational Analysis of an Experimental Approach to Search for Free Neutron-Antineutron Oscillations Based on Coherent Neutron and Antineutron Multilayer Mirror Reflection Kylie Dickerson An observation of neutron-antineutron oscillations ($n$ $\textendash$ $\bar{n}$), which violate both B and B $\textendash$ L conservation, would constitute a scientific discovery of fundamental importance to physics and cosmology. A stringent upper bound on its transition rate would make an important contribution to our understanding of the baryon asymmetry of the Universe by eliminating the postsphaleron baryogenesis scenario in the light quark sector. We present a quantitative analysis of the theoretical performance of certain types of $n$/$\bar{n}$ multilayer mirrors. Selecting materials with a large contrast in the neutron scattering length density and a continuous distribution of thicknesses can minimize, for sufficiently small transverse momenta of $n$/$\bar{n}$, the relative phase shift of the $n$ and $\bar{n}$ components upon reflection [1], allowing for sufficient coherence to benefit from the greater phase space acceptance a multilayer mirror can provide. We make use of a recent theoretical analysis [2] to estimate the antineutron optical potentials. [1] V. V. Nesvizhevsky et al., Phys. Rev. Lett. 122, 221802 (2019). [2] K. V. Protasov et al., Phys. Rev. D 102, 075025 (2020). [Preview Abstract] |
Saturday, April 17, 2021 4:21PM - 4:33PM Live |
E13.00004: A Measurement of Proton, Deuteron, Triton and Alpha Particle Emission after Nuclear Muon Capture on Al, Si and Ti Andrew Edmonds The AlCap experiment has measured the emission rate and energy spectra of protons, deuterons, tritons and alpha particles associated with the nuclear capture of muons stopped in Al, Si, and Ti at PSI. These measurements quantify an important nuclear physics hit background to the Mu2e and COMET experiments, which will search for charged lepton flavor violation at an unprecedented level of sensitivity. Detailed information on the rates and energy spectra of the emitted heavy particles in the capture process is important to the design of the background-reducing aspects of these experiments. The results are also relevant for understanding the nuclear physics of these rare reaction branches. In this talk, I will describe the experiment and present the results. [Preview Abstract] |
Saturday, April 17, 2021 4:33PM - 4:45PM Live |
E13.00005: 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] |
Saturday, April 17, 2021 4:45PM - 4:57PM Live |
E13.00006: Status Update for the UCN$\tau$ Neutron Lifetime Experiment Francisco Gonzalez The UCN$\tau$ experiment at Los Alamos National Laboratory measures the neutron lifetime by holding ultracold neutrons (UCN) in a magneto-gravitational trap for variable holding times. Precision neutron beta decay measurements provide an important insight into the Standard Model. A combination of measurements of decay correlation coefficients and the neutron lifetime generates an independent, competitive, determination of the CKM matrix element $V_{ud}$. UCN$\tau$ utilizes a permanent magnet array to prevent neutron-wall interactions and thus minimizes non-decay neutron loss mechanisms. During 2017 and 2018, the UCN$\tau$ collaboration gathered enough data to produce a measurement of $\tau_n$ with an expected statistical uncertainty below 0.3s, and an expected systematic uncertainty below +0.2s. We will present the present status of the experiment and analysis, as well as improvements made to achieve UCN$\tau$’s goal of a total uncertainty below 0.25s. [Preview Abstract] |
Saturday, April 17, 2021 4:57PM - 5:09PM Live |
E13.00007: Large-$N_c$ Analysis of the Two-Nucleon Neutrinoless Double Beta Decay and Isospin-Breaking Contact Terms Thomas Richardson, Matthias Schindler, Saori Pastore, Roxanne Springer Nuclear matrix elements (NMEs) are an essential ingredient for experimental searches for neutrinoless double beta decay. It was shown by Cirigliano et al. that a $nn \to pp e^- e^-$ contact term is required at leading order for the light Majorana exchange mechanism in the context of chiral effective field theory (ChEFT). An estimate for the corresponding low energy coefficient was obtained through its relation to charge independence breaking two-nucleon interactions. Here, the combined large-$N_c$, where $N_c$ is the number of quark colors, and ChEFT framework is used to establish theoretical constraints for undetermined low energy coefficients and to justify the assumptions that underpin the estimate of this contact term. Additionally, a large-$N_c$ hierarchy of isospin-breaking two-nucleon interactions is elucidated that agrees with phenomenological analyses. [Preview Abstract] |
Saturday, April 17, 2021 5:09PM - 5:21PM Live |
E13.00008: DSSD Characterization for the Beta-decay Paul Trap L. Varriano, G. Savard, J. A. Clark, N. D. Scielzo, D. Burdette, M. T. Burkey, A. T. Gallant, T. Y. Hirsh, B. Longfellow The Beta-decay Paul Trap (BPT) at Argonne National Laboratory measures the beta-neutrino angular correlation coefficient $a_{\beta \nu}$ in the Gamow-Teller decay of $^8$Li and $^8$B (decaying to $^8$Be$^{*} \rightarrow$ 2$\alpha$) to search for a tensor component in the weak interaction, a beyond-Standard Model possibility. The BPT has an ultimate measurement goal of 0.1\% uncertainty in $a_{\beta \nu}$. Two of the remaining systematic uncertainties that must be overcome to achieve the measurement goals are related to the cuts to the data and to alpha energy losses due to detector effects. Both of these systematic uncertainties can be improved through a better understanding of the detector response of the double-sided silicon strip detectors (DSSDs) in use. Of particular interest is a characterization of the interstrip gap region of the detector, where electron-hole pairs can be trapped by the passivated top layer and affect the pulse height to energy ratio for approximately 1\% of events. A DSSD used by the BPT was characterized at ATLAS using an alpha beam at several different energies; preliminary results will be presented. In addition, other improvements for the next iteration of the BPT will be discussed. [Preview Abstract] |
Saturday, April 17, 2021 5:21PM - 5:33PM Live |
E13.00009: Analysis of Gamma Ray Detector Data for the NDTGamma Experiment Gabija Ziemyte, Christopher Crawford The goal of the NDTGamma experiment is to measure effects of the weak nuclear force in the reaction of neutron capture on heavy hydrogen, producing a gamma ray with 6.2 MeV of energy. Initial tests of this experiment were carried out in collaboration with NOPTREX at the Los Alamos National Laboratory at FP 12 at LANSCE using a small 4x4 CsI(TI) detector array and a D2O target. The detector pulses were analyzed using digital signal processing algorithms, and a goal of the initial tests was to demonstrate fast pulse counting techniques for 6.2 MeV gamma rays. I will present these algorithms and the resulting gamma ray spectrum from this test run, which will demonstrate the suitability of these components for the full 100-detector array in the future NDTGamma experiment. [Preview Abstract] |
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