April 29 2025 (in-person)

Zack Hall ( NSF Fellow and LBNL)

Host: André Walker-Loud

Title: A sub-percent Determination of the Nucleon Axial Coupling with Lattice Quantum Chromodynamics

Abstract: The nucleon axial coupling, gA, plays a critical role in determining the free neutron lifetime and additional nuclear processes of interest. In our work we utilize lattice quantum chromodynamics (LQCD) as a non-perturbative method to determine the axial coupling from Standard Model QCD interactions between quarks and gluons. As lattice calculations of gA continue to push the boundaries of precision, it is necessary to quantify and control all sources of systematic errors associated with this framework. In this talk I will discuss gA in the context of low-energy precision physics and outline the first lattice determination of the axial coupling at the sub-percent level.

May 15 2025 (in-person)

Michael Klasen ( Universität Münster)

Host: Volker Koch

Title: Nuclear PDFs after 10 years of LHC data

Abstract: We discuss the conceptual basis, present knowledge and recent progress in the field of global analysis of nuclear parton distribution functions (PDFs). After introducing the theoretical foundations and methodological approaches for the extraction of nuclear PDFs from experimental data, we review how different measurements in fixed-target and collider experiments provide increasingly precise constraints on various aspects of nuclear PDFs, including shadowing, antishadowing, the EMC effect, Fermi motion, flavor separation, deuteron binding, target-mass and other higher-twist effects. Particular emphasis is given to measurements carried out in proton-lead collisions at the Large Hadron Collider, which have revolutionized the global analysis during the past decade. These measurements include electroweak-boson, jet, light-hadron, and heavy-flavor observables. We also outline the expected impact of the future Electron Ion Collider and discuss the role and interplay of nuclear PDFs with other branches of nuclear, particle and astroparticle physics.

June 17 2025 (in-person)

Maciej Lewicki ( Institute of Nuclear Physics, Kraków)

Host: Spencer Klein

Title: Evidence of isospin-symmetry violation in high-energy collisions of atomic nuclei 

Abstract: Strong interactions preserve an approximate isospin symmetry between up (u) and down (d) quarks, part of the more general flavor symmetry. In the case of K meson production, if this isospin symmetry were exact, it would result in equal numbers of charged (K+ and K−) and neutral (K0 and K0bar) mesons produced in collisions of isospin-symmetric atomic nuclei.

In this talk, I will present recent experimental evidence of isospin-symmetry violation in high-energy argon-scandium collisions at √sₙₙ = 11.9A GeV, as observed by the NA61/SHINE collaboration. The measured K⁺, K⁻, and Kₛ⁰ yields at mid-rapidity show an unexpected ~18% excess of charged over neutral kaons, significantly exceeding model predictions based on isospin symmetry and neutron-proton asymmetry. The experimental setup, measurement methods, theoretical models, and implications of this discrepancy will be discussed.