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.

May 20 2025 (in-person)

Anna M. Stasto (Penn State U.)

Host: Feng Yuan

Title: Inclusive charm photoproduction in ultraperipheral collisions at the LHC

Abstract: Ultraperipheral collisions (UPCs) of nuclei at high energies offer unique opportunity to explore the nuclear structure in a clean environment. UPCs occur when two nuclei scatter at impact parameters that exceed the sum of nuclear radii. The UPCs lead to large photonuclear cross sections. In UPC processes involving jets or heavy quarks, large scale allows for perturbative description of the process, and thus such processes can serve as good probes of the nuclear structure. We present the calculation of the  inclusive D0 production cross section in UPC PbPb collisions at the LHC using the Generalized photon-nucleus FONLL framework. In this approach the heavy quark production is computed using the FONLL framework developed previously by Cacciari-Frixione-Nason for ep collisions,  and includes additional electromagnetic corrections to describe the  photoproduction cross section in UPC heavy ion collisions. The calculations are validated against the D* photoproduction cross section from HERA. The predictions for D0 cross section as a function of rapidity and transverse momentum of the D0 meson are presented and compared to the preliminary results from UPC collisions measured by CMS. The sensitivity of the results is studied, when different choices of parton distribution functions and fragmentation functions are made, as well as a function of variation in renormalization and factorization scale dependence.

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.