After nearly a decade since jet substructure first emerged as a powerful probe of the quark–gluon plasma created in heavy-ion collisions, the field has seen remarkable progress and a steady stream of new ideas. At the same time, the increasing sophistication of substructure observables has highlighted important open questions and limitations in our current understanding of jet fragmentation in the presence of dense QCD matter.
Looking ahead to the next decade—with the upcoming LHC Run-4 placing strong emphasis on hard probes, and with the parallel development of an expanded small-systems program—it is timely to assess which aspects of jet-quenching theory require further development, and how they can be leveraged to deepen our understanding of jet substructure.
This Institute aims to bring together the theoretical and experimental communities to make progress on these goals. Building on the success of the first iteration of this workshop at CERN in 2017, the meeting will be organized as a combination of talks and free time for discussion and dedicated collaboration. The Institute will run for two weeks. In each week, talks will be concentrated in the first half, with free time scheduled for the evenings and the latter part of the week.
The following questions will be given the main focus of this Institute:
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What is the current status of the theoretical ingredients describing jet evolution in a QCD medium?
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Which jet substructure observables can be computed in heavy-ion collisions in a controlled and systematic way?
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What insights into small systems can be gained from jet substructure measurements?
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Which future observables would be most impactful for both theory and experiment?
As a final product of the workshop, we envision a brief report summarising the status of the discussions, following up on the successful 2017 report.
Registration deadline: October 5th 2026