This workshop is the fifth edition of the International Small Systems workshop series, continuing a focused effort to understand how collective phenomena emerge in Quantum Chromodynamics (QCD).
Building on the progress of previous meetings, this edition expands the discussion from small collision systems to jets and other multi-scale probes, reflecting the recent evolution of the field. Recent collider measurements have revealed signatures of collectivity in a remarkably wide range of systems, including pp, pA, light-ion, photonuclear and jet-tagged events. These observations challenge traditional distinctions between small and large systems, soft and hard probes, and initial- and final-state dynamics. A central aim of the workshop is to place these developments within a unified, scale-dependent QCD framework, and to clarify what they reveal about the emergence of many-body dynamics from microscopic strong interactions.
The workshop emphasizes that collective phenomena, such as long-range correlations, multiparticle cumulants, jet–medium correlations, polarization effects, and femtoscopic observables, are inherently non-perturbative manifestations of QCD. While perturbative methods successfully describe the production of hard probes, the emergence of collective behavior reflects strong coupling, coherence, and many-body dynamics. Jets, in particular, occupy a unique position at the interface of perturbative production and non-perturbative response, making them powerful differential probes of emergent QCD matter. In addition to hydrodynamic and kinetic approaches, the workshop also explicitly explores novel perspectives such as quantum correlations and entanglement as complementary ways of organizing multiparticle dynamics.
The goal of the workshop is not consensus, but clarity: to identify robust observations, expose open questions, and encourage bold, forward-looking ideas that may guide future experiments and theory. To preserve its interactive character, the workshop is intentionally small and invitation-only. Talks and discussion sessions are structured to emphasize provocation and debate rather than comprehensive result reporting.