Uncovering tau leptons-enriched semi-visible jets at the LHC

Abstract This Letter proposes a new signature for confining dark sectors at the Large Hadron Collider. Under the assumption of a QCD-like hidden sector, hadronic jets containing stable dark bound states could manifest in proton-proton collisions. We present a simplified model with a $$Z'$$ Z ′ boson yielding the production of jets made up of dark bound states and subsequently leading to the decays of those that are unstable to $$\tau $$ τ leptons and Standard Model quarks. The resulting signature is characterised by non-isolated $$\tau $$ τ lepton pairs inside semi-visible jets. We estimate the constraints on our model from existing CMS and ATLAS analyses. We propose a set of variables that leverage the leptonic content of the jet and exploit them in a supervised jet tagger to enhance the signal-to-background separation. Furthermore, we discuss the performance and limitations of current triggers for accessing sub-TeV $$Z'$$ Z ′ masses, as well as possible strategies that can be adopted by experiments to access such low mass regions. We estimate that with the currently available triggers, a high mass search can claim a $$5 \sigma $$ 5 σ discovery (exclusion) of the $$Z'$$ Z ′ boson with a mass up to 4.5 TeV (5.5 TeV) with the full Run 2 data of the LHC when the fraction of unstable dark hadrons decaying to $$\tau $$ τ lepton pairs is around $$50\%$$ 50 % , and with a coupling of the $$Z'$$ Z ′ to right-handed up-type quarks of 0.25. Furthermore, we show that, with new trigger strategies for Run 3, it may be possible to access $$Z'$$ Z ′ masses down to 700 GeV, for which the event topology is still composed of two resolved semi-visible jets.