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 JA: CKM Unitarity and Anomalies in Vus/Vud |
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Chair: Leendert Hayen, North Carolina State University Room: Ballroom B |
Wednesday, October 13, 2021 9:30AM - 10:06AM |
JA.00001: Theory inputs for Vud and Vus extraction Invited Speaker: Chien Yeah Seng Several significant anomalies have been observed in the beta decay of mesons, nucleon and nuclei, in particular the apparent violation of the Cabibbo-Kobayashi-Maskawa (CKM) matrix unitarity involving the matrix elements Vud and Vus, which make them promising avenues for the search of the physics beyond the Standard Model (BSM). However, the current significant level of the observed anomalies is not yet sufficient to declare a discovery, and the major limiting factor is the precision level of the Standard Model (SM) theory inputs instead of experiments. In this talk, I will describe the major theory improvements needed to increase the significance level of the existing beta decay anomalies to 5 standard deviations, assuming that BSM physics is the underlying reason. They include high-precision studies of radiative corrections, isospin-breaking corrections and nuclear structure corrections to various beta decay processes. |
Wednesday, October 13, 2021 10:06AM - 10:42AM |
JA.00002: Lattice QCD Input for the First Row CKM Unitarity Tests Invited Speaker: Luchang Jin I would like to report our recent lattice calculations relates to the QED and strong isospin corrections to pion and kaon (semi-)leptonic decay processes. These decay processes are the primary way to determine V_{us}, needed for the first row CKM unitarity tests. At present accuracy, the QED and strong isospin correction are becoming important. Dispersive analysis can reduce the number of diagrams need lattice calculation. For charged pion semi-leptonic decay, the only relevant diagram is the gamma-W box diagram, which has been calculated to very high precision. In addition to calculating these corrections directly, lattice calculation can be combined with ChPT formula to determine the low energy constants. Lattice calculations can also help determine the gamma-W box diagram in neutron beta decay, which is the major source of uncertainty in determining V_{ud}. This calculation is in progress. |
Wednesday, October 13, 2021 10:42AM - 11:18AM |
JA.00003: New Results from the UCN$\tau$ Neutron Lifetime Experiment Invited Speaker: Francisco M Gonzalez A free neutron provides the simplest example of nuclear $\beta$-decay, leading to a unique suite of tests for fundamental parameters of electroweak theory. The neutron lifetime $\tau_n$, in conjunction with other neutron $\beta$-decay observables, can be used to extract $V_{ud}$ experimentally. The UCN$\tau$ experiment at Los Alamos National Laboratory (LANL) traps ultracold neutrons (UCN) in a magnetogravitational "bottle" for periods of time longer than the neutron lifetime. A permanent magnet Halbach array minimizes neutron losses, ensuring that the loss rates of UCN in UCN$\tau$ generate systematic corrections no greater than the statistical precision of the experiment. The addition of a buffer volume between the UCN source and the trap has improved the ability to reconstruct the number of initially stored neutrons. Potential sources of loss have been benchmarked by using the in-situ "dagger" and "active cleaner" detectors to probe UCN near the trapping threshold. We present the results of three independent, blinded, analyses utilizing $\sim 10^7$ neutrons collected over two calendar years of operation. UCN$\tau$ now reports a lifetime of $877.75 \pm 0.28_{\text{(stat.)}} + 0.22 / - 0.16_{\text{(sys.)}}$~s, directly probing recent developments in $\beta$-decay theory. |
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