Search for pair production of a new heavy quark that decays into a $W$ boson and a light quark in $pp$ collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector

TL;DR

This paper reports a search for new heavy quarks decaying into a W boson and a light quark in proton-proton collisions at 8 TeV, setting mass exclusion limits up to 690 GeV with no evidence found.

Contribution

First search for pair-produced heavy quarks decaying into W and light quarks at 8 TeV with ATLAS, establishing mass exclusion limits and interpreting results in vectorlike quark models.

Findings

No evidence of heavy quark pair production.

Excluded heavy quark masses below 690 GeV at 95% CL.

Set limits on vectorlike quark model parameters.

Abstract

A search is presented for pair production of a new heavy quark ($Q$) that decays into a $W$ boson and a light quark ($q$) in the final state where one $W$ boson decays leptonically (to an electron or muon plus a neutrino) and the other $W$ boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 8$ TeV collected by the ATLAS detector at the LHC. No evidence of $Q\bar{Q}$ production is observed. New chiral quarks with masses below 690 GeV are excluded at 95% confidence level, assuming BR$(Q\to Wq)=1$. Results are also interpreted in the context of vectorlike quark models, resulting in the limits on the mass of a vectorlike quark in the two-dimensional plane of BR$(Q\to Wq)$ versus BR$(Q\to Hq)$.