Abstract

Semi-visible jets are a collider signature that arise from dark sector models with strong dynamics, where dark showers produce final states containing both visible and invisible particles. These signatures pose significant challenges to standard LHC searches, both from a search strategy and modeling perspective,  and therefore motivate a close dialogue between theorists and experimentalists.
In this collider cross talk, we discuss recent progress in the study of semi-visible jets at the LHC, with particular emphasis on lepton-enriched final states and on t-channel production modes, which exhibit characteristic kinematic features and provide enhanced sensitivity to a wide class of dark sector scenarios. We highlight how the presence of leptons can improve triggering, background suppression, and the interpretability of the results.
We then introduce the Lund Jet Plane as a unifying framework for dark showers, showing how it captures the multi-scale structure of radiation in confining dark sectors and provides a physically motivated  representation of semi-visible jet substructure. This theoretical perspective forms the basis for modern jet-tagging approaches.
Building on this framework, we present Graph Neural Network–based jet identification techniques that exploit Lund-plane-inspired graph representations to discriminate semi-visible jets from QCD backgrounds. These methods leverage the hierarchical and multi-scale information encoded in the Lund Plane, offering both high sensitivity and increased robustness with respect to modeling uncertainties.

Speakers

Annapaola De Cosa is an Assistant Professor of Particle Physics at ETH Zurich and an SNSF Eccellenza Fellow. She obtained her PhD in Physics in 2013 from the University of Naples, working within the CMS experiment at CERN. Her research broadly focuses on searches for
 new physics at the LHC, combining experimental analyses, phenomenological insight, and advanced machine-learning techniques. In recent years, she has led pioneering efforts on semi-visible jets and dark showers. She is currently a co-leader of the LHC Dark Shower Task Force within the LHC BSM Working Group.

Tim Cohen is a CERN staff member (on leave from an Associate Professor position at the University of Oregon, USA). He got his PhD from the University of Michigan, USA in 2011.  He has broad interests in beyond the Standard Model theory, including finding new probes of dark sector strong dynamics at the LHC.