April 08 2025 (in-person)

Joseph Moscoso ( LBNL)

Host: Andre Walker-Loud

Title: Testing the Two-Hadron Finite-Volume Formalism with a low-energy lattice EFT

Abstract: The study of two-hadron matrix elements and form factors is critical for the success of several planned experimental searches for new physics which utilize low-energy nuclear environments. Lattice QCD calculations of relevant processes rely on a recently derived finite-volume formalism for computing 2+J->2 amplitudes.  In this work, I will discuss consistency checks on the formalism using lattice calculations of a low-energy non-relativistic EFT. Numerical calculations of the scattering system with a tunable interaction allows us to test the application of the formalism to real and virtual bound states. I will discuss the case of the electromagnetic form factors of two-nucleon systems.

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.