Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session S05: The Axial Structure of the Nucleon and Its ImplicationsInvited Session
|
Hide Abstracts |
Sponsoring Units: GHP DNP Chair: Albert Young, North Carolina State University Room: A123-125 |
Monday, April 16, 2018 1:30PM - 2:06PM |
S05.00001: The axial coupling of the nucleon from Quantum Chromodynamics Invited Speaker: Chia Cheng Chang The axial coupling of the nucleon, $g_A$, is a fundamental property of neutrons and protons. The long-range nuclear force between nucleons and the $\beta$-decay rate of a free neutron both depend on $g_A^2$. This coupling therefore underpins all of low-energy nuclear physics, controlling, for example, the primordial composition of the universe. While the value of $g_A$ is, in principle, determined by the fundamental theory of nuclear strong interactions, Quantum Chromodynamics (QCD), it is daunting to compute, as QCD is non-perturbative and has evaded an analytic solution. Lattice QCD provides a rigorous, non-perturbative definition of the theory through a discretised formulation which can be numerically implemented. Using an innovative computational method, we resolve the two outstanding challenges identified by the lattice QCD community for determining $g_A$: we demonstrably control excited state lattice artefacts and are able to utilise exponentially more precise numerical data resulting in the determination $g_A^{QCD} = 1.275\pm 0.012$, compatible with the experimentally measured value and with unprecedented precision of 0.95\%. Prior to the work presented here, it was estimated, using standard methods of the field, that a 2\% precision would only be achievable with the next-generation of leadership computing facilities by 2020. This calculation signals a new era of precision lattice QCD applications to high-impact experimental searches for physics beyond the Standard Model in nuclear environments. [Preview Abstract] |
Monday, April 16, 2018 2:06PM - 2:42PM |
S05.00002: Precision determination of the ratio of axial-vector and vector coupling constants from neutron beta decay Invited Speaker: Bastian Maerkisch Within the standard model of particle physics, only two free parameters determine the decay of the free neutron, where we profit from the precise determination of the Fermi coupling constant in muon decay. These parameters are the ratio of axial-vector and vector coupling constants $\lambda = g_A / g_V$ and the CKM mixing matrix element $V_\textrm{ud}$. With about a dozen experimental observables the problem of the determination of these parameters is largely over-constrained and hence enables the vivid search for non $V-A$ couplings in this process. We present the result of the neutron decay spectrometer \textsc{Perkeo~III} on the ratio of coupling constants which was derived from a measurement of the beta asymmetry in polarized neutron beta decay with a precision of $\Delta\lambda = 6\times 10^{-4}$. The instrument was installed and operated at the high flux neutron source of the Institut Laue-Langevin, Grenoble, France. A pulsed cold neutron beam was used to control or eliminate major sources of systematic error. The presentation will conclude with a status report on the follow-up instrument PERC, which is currently under construction at the MLZ, Garching, Germany. The aim of PERC is an improved measurement of several decay correlations in neutron beta decay by an order of magnitude. [Preview Abstract] |
Monday, April 16, 2018 2:42PM - 3:18PM |
S05.00003: The nucleon axial radius, its determination and implications Invited Speaker: Richard Hill The nucleon axial radius, $r_A^2$, is an important quantity governing the nucleon response to electroweak probes. Its uncertainty dominates the error bar for neutrino-nucleon charged current quasielastic scattering, a key signal process at long baseline neutrino experiments. Recent developments are reviewed, including the reanalysis of data from neutrino scattering at deuterium bubble chambers and the reinterpretation of muon capture on hydrogen as a measurement of $r_A^2$; these processes currently provide the best constraints on $r_A^2$. The talk concludes with an overview of current and future theoretical and experimental efforts for improved measurements of $r_A^2$. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700