Dark Matter Lurking in Semi-Visible Jets

Models of dark matter featuring a strongly-coupled hidden sector have emerged as compelling alternatives to traditional weakly interacting massive particle (WIMP) scenarios. In particular, semi-visible jets with final states containing both visible and invisible particles produced via a confining dark sector offer distinctive collider signatures. This study investigates such models in the context of resonant production of a heavy 𝑍' mediator that couples the Standard Model to a hidden QCD-like sector. The resulting events exhibit jets with substantial missing transverse momentum aligned with the jet direction, a phase space usually overlooked in the traditional searches.

We explore the phenomenology of these signatures using ATLAS Run 2 data. Machine learning methods are used to select these dark showers and reject the dominant background of mismeasured multijet events, including an anomaly detection approach to preserve broad sensitivity to a variety of BSM topologies. A resonance search is performed by fitting the transverse mass spectrum based on a functional form background estimation, and results are presented as limits on the production cross section of semi-visible jet signals.