LHC vector resonance searches in the tt¯ Z final state

Abstract

LHC searches for BSM resonances in l+l−,jj,tt¯ , γγ and VV final states have so far not resulted in discovery of new physics. Current results set lower limits on mass scales of new physics resonances well into the O(1) TeV range, assuming that the new resonance decays dominantly to a pair of Standard Model particles. While the SM pair searches are a vital probe of possible new physics, it is important to re-examine the scope of new physics scenarios probed with such final states. Scenarios where new resonances decay dominantly to final states other than SM pairs, even though well theoretically motivated, lie beyond the scope of SM pair searches. In this paper we argue that LHC searches for (vector) resonances beyond two particle final states would be useful complementary probes of new physics scenarios. As an example, we consider a class of composite Higgs models, and identify specific model parameter points where the color singlet, electrically neutral vector resonance ρ0 decays dominantly not to a pair of SM particles, but to a fermionic top partner Tf1 and a top quark, with Tf1 → tZ. We show that dominant decays of ρ0 → Tf1t in the context of Composite Higgs models are possible even when the decay channel to a pair of Tf1 is kinematically open. Our analysis deals with scenarios where both mρ and mTf1 are of O(1) TeV, leading to highly boosted tt¯ Z final state topologies. We show that the particular composite Higgs scenario we consider is discoverable at the LHC13 with as little as 30 fb−1, while being allowed by other existing experimental constraints.