LHC vector resonance searches in the $t\bar{t} Z$ final state

TL;DR

This paper explores the potential of LHC searches for vector resonances decaying into complex final states like $t\bar{t}Z$, focusing on scenarios where new resonances decay into non-standard particles, thus broadening the scope of new physics detection.

Contribution

It introduces the idea of searching for vector resonances decaying into non-SM particle combinations, specifically in the $t\bar{t}Z$ final state, within composite Higgs models.

Findings

Dominant decay of $\rho_0$ to $T_{f1} t$ is possible even when $\rho_0$ can decay to $T_{f1} T_{f1}$.

Such $t\bar{t}Z$ final states are discoverable at LHC13 with 30 fb$^{-1}$.

The scenario is consistent with existing experimental constraints.

Abstract

LHC searches for BSM resonances in $l^+ l^-, \, jj, \, t\bar{t}, \gamma \gamma$ 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 $\mathcal{O}(1)$ 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 $\rho_0$ decays dominantly not to a pair of SM particles, but to a fermionic top partner $T_{f1}$ and a top quark, with $T_{f1} \rightarrow tZ$. We show that dominant decays of $\rho_0 \rightarrow T_{f1} t$ in the context of Composite Higgs models are possible even when the decay channel to a pair of $T_{f1}$ is kinematically open. Our analysis deals with scenarios where both $m_\rho$ and $m_{T_{f1}}$ are of $\mathcal{O}(1)$ TeV, leading to highly boosted $t\bar{t}Z$ 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.