Searches for VLQs and LQs from the ATLAS Experiment

TL;DR

This work surveys ATLAS searches for beyond-the-Standard-Model states—vector-like quarks, vector-like leptons, and leptoquarks—using the full Run 2 dataset at $\sqrt{s}=13$ TeV. It emphasizes single-production channels and diverse final states (e.g., $Wb$, $Zt$, $Ht$, mono-top, lepton-jet resonances) to constrain masses and couplings, notably $m_{\mathrm{VLQ}}$, $\kappa$, and Yukawa couplings $y$. The results yield extensive exclusion limits, with VLQ masses pushed to multi-TeV scales (e.g., $m_T$, $m_Y$ in the 1.4–2.4 TeV range in various channels) and LQ masses reaching several TeV depending on $y$, while VLL scenarios within 4321 models are constrained up to about 910 GeV. Collectively, these findings tighten the viable parameter spaces for Composite Higgs, 4321, and related GUT-inspired models, and demonstrate the continued sensitivity of ATLAS to singly produced heavy states beyond the Standard Model.

Abstract

The Standard Model of particle physics explains many natural phenomena yet remains incomplete. Vectorlike quarks and leptoquarks lie at the heart of many extensions to the Standard Model seeking to address the hierarchy problem, or the flavour sector anomalies. These proceedings present the new results from searches with the ATLAS detector at the LHC.

Figures (9)

• Figure 1: Examples of single production and decay of VLQs.
• Figure 2: Exclusion limits of $Y \rightarrow Wb (1\ell)$ in the width -- mass plane. From EXOT-2018-60.
• Figure 3: Upper cross section limits as a function of the VLQ mass for the $T/Y \rightarrow Wb$ search in the all-hadronic channel. From EXOT-2022-43.
• Figure 4: Upper cross section limits on $T \rightarrow Z(\nu\nu)t$ as a function of mass. From EXOT-2022-40.
• Figure 5: Lower mass limit on $T$ as a function of the relative coupling $\xi_W$ (which is $BR(T\rightarrow Wb)$ for large $m_T$). From EXOT-2021-02.