Search for single-production of vector-like quarks decaying into $Wb$ in the fully hadronic final state in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

TL;DR

This paper reports a search for vector-like quarks decaying into W bosons and b quarks in fully hadronic final states using 13 TeV proton-proton collision data from the ATLAS detector, setting new mass exclusion limits.

Contribution

The study presents the first search for vector-like T and Y quarks decaying into Wb in fully hadronic final states at 13 TeV with the ATLAS detector, establishing new mass limits.

Findings

No significant excess observed in data.

Mass limits for Y quarks: 2.0 TeV (κ=0.5), 2.4 TeV (κ=0.7).

Mass limits for T quarks: 1.4 TeV (κ=0.5), 1.9 TeV (κ=0.7).

Abstract

A search for $T$ and $Y$ vector-like quarks produced in proton-proton collisions at a centre-of-mass energy of $13\,\text{TeV}$ and decaying into $Wb$ in the fully hadronic final state is presented. The search uses 139 fb$^{-1}$ of data collected by the ATLAS detector at the LHC from 2015 to 2018. The final state is characterised by a hadronically decaying $W$ boson with large Lorentz boost and a $b$-tagged jet, which are used to reconstruct the invariant mass of the vector-like quark candidate. The main background is QCD multijet production, which is estimated using a data-driven method. Upon finding no significant excess in data, mass limits at 95% confidence level are obtained as a function of the global coupling parameter, $\kappa$. The observed lower limits on the masses of $Y$ quarks with $\kappa = 0.5$ and $\kappa = 0.7$ are 2.0 TeV and 2.4 TeV, respectively. For $T$ quarks, the observed mass limits are 1.4 TeV for $\kappa = 0.5$ and 1.9 TeV for $\kappa = 0.7$.