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 EA: New Precision Results in Hadronic Physics with Electroweak Probes |
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Chair: Cynthia Keppel, Jefferson Lab Room: Ballroom B |
Tuesday, October 12, 2021 11:45AM - 12:21PM |
EA.00001: Precision Measurement of the π0 Lifetime Invited Speaker: Liping Gan As the lightest and the simplest hadron, π0 plays a crucial role in our understanding of the symmetry structure of low-energy QCD. The π0→γγ decay width offers a fundamental test of the QCD predictions based on the chiral anomaly and spontaneous chiral symmetry breaking. The theoretical calculations over the past two decades have reached 1% precision in the decay amplitude of the π0 into two photons. The experimental measurement of this parameter with a comparable accuracy provides a stringent test of QCD. The PrimEx collaboration at Jefferson Lab has developed and performed two experiments (PrimEx I&II) to measure the π0 radiative decay width via the Primakoff effect. The published result, Γ(π0→γγ)=7.802±0.052±0.105 eV, has a 1.5% total uncertainty. It agrees to the leading-order chiral anomaly and is about 2σ lower than the high-order QCD predictions. The details of measurement and the physics impact will be discussed. |
Tuesday, October 12, 2021 12:21PM - 12:57PM |
EA.00002: Probing the nucleon structure using Drell-Yan process at SeaQuest Invited Speaker: Shivangi Prasad SeaQuest is a fixed-target experiment at Fermilab using 120 GeV proton beam from the Main Injector. The experiment utilizes the Drell-Yan process to probe the anti-quark distributions inside the target nucleon. In particular, the Drell-Yan cross section ratios for liquid deuterium over hydrogen allows the measurement of sea quark asymmetry, d̅(x)/u̅(x), for x ranging from 0.13 to 0.45, extending the measurement of the previous experiment NuSea/E866 to larger x. The knowledge of the sea-quark asymmetry at large x is important for understanding the non-perturbative origin of the nucleon sea. Recent results on light sea-quark flavor asymmetry and its comparison with theoretical calculations and recent global PDFs will be presented in this talk. Additionally, SeaQuest experiment also provides the opportunity to study several physics topics. One example is the measurement of Drell-Yan differential cross sections, which allow improved constraints on magnitude and shape of sea-quark distributions. In particular, the p+d absolute cross section is sensitive to the d̅(x)+u̅(x) distribution at large x region. Another example is the measurement of charmonium production, which is sensitive to the gluon distributions. Current status of these analyses will also be reported. |
Tuesday, October 12, 2021 12:57PM - 1:33PM |
EA.00003: CREX: Precision Measurement of the Neutral Weak Form Factor in Elastic Electron-48Ca Scattering Invited Speaker: Caryn Palatchi A measurement of the neutron skin of the modestly sized, neutron rich 48Ca nucleus can provide an important benchmark for nuclear theory. The RMS radius of the neutron distribution in the nucleus is measured via the parity violating asymmetry in longitudinally polarized elastic electron-nucleus scattering. While the electroweak nature of this parity violating interaction lends itself to cleanly interpretable results it also presents considerable experimental challenges. The CREX collaboration successfully completed data collection in 2020 at Jefferson Lab employing the CEBAF accelerator. Precise measurement of the neutron skin of 48Ca provides unique experimental input to help bridge ab-initio theoretical approaches and the nuclear density functional theory. Analysis of the experimental result and our understanding of its impact regarding nuclear structure will be presented. |
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