Search for pair-production of vector-like quarks in $pp$ collision events at $\sqrt{s}=13$ TeV with at least one leptonically decaying $Z$ boson and a third-generation quark with the ATLAS detector

Abstract

A search for the pair-production of vector-like quarks optimized for decays into a $Z$ boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to 139 fb${}^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV, collected in 2015-2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a $Z$ boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of $b$-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted $W$, $Z$, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners $T$ and $B$ of the top and bottom quarks, respectively. In the singlet model, the limits allow $m_T>1.27$ TeV and $m_B>1.20$ TeV. In the doublet model, allowed masses are $m_T>1.46$ TeV and $m_B>1.32$ TeV. In the case of 100% branching ratio for $T\to Zt$ and 100% branching ratio for $B\to Zb$, the limits allow $m_T>1.60$ TeV and $m_B>1.42$ TeV, respectively.

26 pages plus author list, 44 pages in total, 8 figures, 4 tables. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2018-58

References in corpus (20)

• Deep Learning in Neural Networks: An Overview
• Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC
• Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC
• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• An Introduction to PYTHIA 8.2
• Parton distributions for the LHC
• New parton distributions for collider physics
• Event generation with SHERPA 1.1
• A parton shower algorithm based on Catani-Seymour dipole factorisation
• Single-top Wt-channel production matched with parton showers using the POWHEG method
• Two-loop soft anomalous dimensions for single top quark associated production with a W- or H-
• -- HATHOR -- HAdronic Top and Heavy quarks crOss section calculatoR
• Next-to-next-to-leading-order collinear and soft gluon corrections for t-channel single top quark production
• NNLL resummation for s-channel single top quark production
• HATHOR for single top-quark production: Updated predictions and uncertainty estimates for single top-quark production in hadronic collisions
• Muon reconstruction and identification efficiency in ATLAS using the full Run 2 $pp$ collision data set at $\sqrt{s}=13$ TeV
• Warped Gravitons at the LHC and Beyond
• Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions
• Optimisation of large-radius jet reconstruction for the ATLAS detector in 13 TeV proton-proton collisions
• New sensitivity of current LHC measurements to vector-like quarks

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• Vector-Like Top Quark Production via an Electroweak Dipole Moment at a Muon Collider
• Global analysis and LHC study of a vector-like extension of the Standard Model with extra scalars
• Search for charged Higgs bosons through vector-like top quark pair production at the LHC
• Pair production of the singlet vector-like B quark at the CLIC
• The Hierarchy Problem and the Top Yukawa: An Alternative to Top Partner Solutions
• A search for bottom-type vector-like quark pair production in dileptonic and fully hadronic final states in proton-proton collisions at $\sqrt{s}$ = 13 TeV
• Naturalness-motivated composite Higgs model for generating the top Yukawa coupling
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• Exploring vector-like $B$-quark pair production at CLIC in fully hadronic final states
• Restoring Naturalness via Conjugate Fermions
• Probing Light Scalars and Vector-like Quarks at the High-Luminosity LHC
• Searching for single production of vectorlike quarks decaying into Wb at a future muon-proton collider
• Tagging ultra-boosted jets at FCC-hh using machine learning techniques
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