Combination of the searches for pair-produced vector-like partners of the third-generation quarks at $\sqrt{s} =$ 13 TeV with the ATLAS detector

TL;DR

This paper combines multiple ATLAS searches at 13 TeV to set improved limits on vector-like quarks, excluding certain mass ranges for singlet and doublet scenarios with no significant deviation from the Standard Model observed.

Contribution

It presents a combined analysis of various decay channels to enhance sensitivity and set more stringent mass exclusion limits for vector-like quarks.

Findings

Excluded singlet T quark masses below 1.31 TeV.

Excluded singlet B quark masses below 1.22 TeV.

Excluded T and B doublet masses below 1.37 TeV.

Abstract

A combination of the searches for pair-produced vector-like partners of the top and bottom quarks in various decay channels ($T$$\rightarrow$$Zt/Wb/Ht$, $B$$\rightarrow$$Zb/Wt/Hb$) is performed using 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the Standard Model background prediction in all individual searches. Therefore, combined 95% confidence-level upper limits are set on the production cross-section for a range of vector-like quark scenarios, significantly improving upon the reach of the individual searches. Model-independent limits are set assuming the vector-like quarks decay to Standard Model particles. A singlet $T$ is excluded for masses below 1.31 TeV and a singlet $B$ is excluded for masses below 1.22 TeV. Assuming a weak isospin $(T,B)$ doublet and $|V_{Tb}| \ll |V_{tB}|$, $T$ and $B$ masses below 1.37 TeV are excluded.