Search for production of vector-like quark pairs and of four top quarks in the lepton-plus-jets final state in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

Abstract

A search for pair production of vector-like quarks, both up-type ($T$) and down-type ($B$), as well as for four-top-quark production, is presented. The search is based on $pp$ collisions at $\sqrt{s}=8$ TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 20.3 fb${}^{-1}$. Data are analysed in the lepton-plus-jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets. Dedicated analyses are performed targeting three cases: a $T$ quark with significant branching ratio to a $W$ boson and a $b$-quark ($T\bar{T}\to Wb$+X), and both a $T$ quark and a $B$ quark with significant branching ratio to a Higgs boson and a third-generation quark ($T\bar{T}\to Ht$+X and $B\bar{B}\to Hb$+X respectively). No significant excess of events above the Standard Model expectation is observed, and 95% CL lower limits are derived on the masses of the vector-like $T$ and $B$ quarks under several branching ratio hypotheses assuming contributions from $T\to Wb$, $Zt$, $Ht$ and $B\to Wt$, $Zb$, $Hb$ decays. The 95% CL observed lower limits on the $T$ quark mass range between 715 GeV and 950 GeV for all possible values of the branching ratios into the three decay modes, and are the most stringent constraints to date. Additionally, the most restrictive upper bounds on four-top-quark production are set in a number of new physics scenarios.

67 pages + author list + cover pages (84 pages total), 33 figures, 10 tables, submitted to JHEP. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2013-18/

References in corpus (41)

• 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
• PYTHIA 6.4 Physics and Manual
• Parton distributions for the LHC
• Matching NLO QCD computations with Parton Shower simulations: the POWHEG method
• New parton distributions for collider physics
• Event generation with SHERPA 1.1
• Implications of CTEQ global analysis for collider observables
• Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions
• Performance of the ATLAS Trigger System in 2015
• 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-
• Single-top hadroproduction in association with a W boson
• Electroweak gauge boson production at hadron colliders through O(alpha_s^2)
• 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
• The PDF4LHC Working Group Interim Recommendations
• Jet energy measurement and its systematic uncertainty in proton-proton collisions at $\sqrt{s}=7$ TeV with the ATLAS detector
• Precise predictions for the Higgs-boson decay H -> W W/Z Z -> 4 leptons
• Measurement of the muon reconstruction performance of the ATLAS detector using 2011 and 2012 LHC proton-proton collision data
• Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton-proton collision data
• The RooFit toolkit for data modeling
• t tbar W and t tbar Z Hadroproduction at NLO accuracy in QCD with Parton Shower and Hadronization effects
• Search for the Standard Model Higgs boson produced in association with top quarks and decaying into $b\bar{b}$ in pp collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector
• Top Compositeness at the Tevatron and LHC
• Color-Octet Scalars of N=2 Supersymmetry at the LHC
• Measurements of normalized differential cross-sections for ttbar production in pp collisions at sqrt(s) = 7 TeV using the ATLAS detector
• Search for pair and single production of new heavy quarks that decay to a $Z$ boson and a third-generation quark in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector
• Search for heavy bottom-like quarks in 4.9 inverse femtobarns of pp collisions at sqrt(s) = 7 TeV
• Heavy Quarks Above the Top at the Tevatron
• Manifestations of Top Compositeness at Colliders
• Search for vector-like $B$ quarks in events with one isolated lepton, missing transverse momentum and jets at $\sqrt{s}=$ 8 TeV with the ATLAS detector
• Muon reconstruction efficiency and momentum resolution of the ATLAS experiment in proton-proton collisions at $\sqrt{s}$=7 TeV in 2010
• Analysis of events with $b$-jets and a pair of leptons of the same charge in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector
• BRIDGE: Branching Ratio Inquiry/Decay Generated Events
• Searching for sgluons in multitop events at a center-of-mass energy of 8 TeV
• Colored Resonances at the Tevatron: Phenomenology and Discovery Potential in Multijets
• Search for pair produced fourth-generation up-type quarks in pp collisions at sqrt(s) = 7 TeV with a lepton in the final state
• Associated production of a Kaluza-Klein excitation of a gluon with a t t(bar) pair at the LHC
• Search for standard model production of four top quarks in the lepton + jets channel in pp collisions at sqrt(s) = 8 TeV
• Search for heavy quarks decaying into a top quark and a W or Z boson using lepton + jets events in pp collisions at sqrt(s) = 7 TeV

Cited by in corpus (118)

• From the trees to the forest: a review of radiative neutrino mass models
• The Giant Radio Array for Neutrino Detection (GRAND): Science and Design
• On the Interpretation of a Possible $\sim 750$ GeV Particle Decaying into $\gamma \gamma$
• Rays of light from the LHC
• Simplified Models vs. Effective Field Theory Approaches in Dark Matter Searches
• Quark Seesaw, Vectorlike Fermions and Diphoton Excess
• Search for vector-like charge 2/3 T quarks in proton-proton collisions at sqrt(s) = 8 TeV
• The 750 GeV $S$-cion: Where else should we look for it?
• Search for vector-like T and B quark pairs in final states with leptons at $\sqrt{s}=$ 13 TeV
• Composite scalars at the LHC: the Higgs, the Sextet and the Octet
• On the 750 GeV di-photon excess
• Indirect Constraints on the Scalar Di-Photon Resonance at the LHC
• Search for pair production of up-type vector-like quarks and for four-top-quark events in final states with multiple $b$-jets with the ATLAS detector
• Vector-like Fermions and Higgs Effective Field Theory Revisited
• Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector
• Direct and indirect signals of natural composite Higgs models
• Search for pair-produced vectorlike B quarks in proton-proton collisions at sqrt(s) = 8 TeV
• Four Tops for LHC
• Twin Baryogenesis
• Decaying Leptophilic Dark Matter at IceCube
• 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
• A Simple $U(1)$ Gauge Theory Explanation of the Diphoton Excess
• Search for pair production of vector-like quarks in the bW$\overline{\mathrm{b}}$W channel from proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Novel signatures for vector-like quarks
• Electroweak Vacuum Stability and Diphoton Excess at 750 GeV
• Search for the Higgs boson produced in association with a vector boson and decaying into two spin-zero particles in the $H\to aa\to 4b$ channel in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Search for single production of a vector-like T quark decaying to a Z boson and a top quark in proton-proton collisions at $\sqrt{s}=$13 TeV
• Interpreting the 750 GeV diphoton excess in minimal extensions of Two-Higgs-Doublet models
• Squarkonium, diquarkonium and octetonium at the LHC and their di-photon decays
• Direct Bounds on Heavy Top-Like Quarks With Standard and Exotic Decays
• Closing the Wedge: Search Strategies for Extended Higgs Sectors with Heavy Flavor Final States
• Vector-like Singlet Quarks: a Roadmap
• The Maximally Symmetric Composite Higgs
• Search for pair production of heavy vector-like quarks decaying into hadronic final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Search for standard model production of four top quarks with same-sign and multilepton final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Search for single production of vector-like quarks decaying into $Wb$ in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Search for single production of vector-like quarks decaying to a top quark and a W boson in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Search for single production of vector-like quarks decaying into $Wb$ in $pp$ collisions at $\sqrt{s}=$ 8 TeV with the ATLAS detector
• Probing Higgs Width and Top Quark Yukawa Coupling from $t\bar{t}H$ and $t\bar{t}t\bar{t}$ Productions
• 750 GeV Diphotons: Implications for Supersymmetric Unification II
• Vector-like top/bottom quark partners and Higgs physics at the LHC
• Flavor Cosmology: Dynamical Yukawas in the Froggatt-Nielsen Mechanism
• A Consistent Theory of Decaying Dark Matter Connecting IceCube to the Sesame Street
• Search for the production of four top quarks in the single-lepton and opposite-sign dilepton final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Constraining $qqtt$ operators from four-top production: a case for enhanced EFT sensitivity
• Simplified Models for Higgs Physics: Singlet Scalar and Vector-like Quark Phenomenology
• Higgs precision study of the 750 GeV diphoton resonance and the 125 GeV standard model Higgs boson with Higgs-singlet mixing
• Search for single production of a vector-like $T$ quark decaying into a Higgs boson and top quark with fully hadronic final states using the ATLAS detector
• Top-philic Scalar Dark Matter with a Vector-like Fermionic Top Partner
• Top Partners Searches and Composite Higgs Models
• Boosted Dark Matter and its implications for the features in IceCube HESE data
• Search for single production of vector-like quarks decaying into a b quark and a W boson in proton-proton collisions at sqrt(s) = 13 TeV
• Search for the production of single vector-like and excited quarks in the $Wt$ final state in $pp$ collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector
• Novel Interpretation Strategy for Searches of Singly Produced Vector-like Quarks at the LHC
• Search for large missing transverse momentum in association with one top-quark in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Interpretation of Vector-like Quark Searches: Heavy Gluons in Composite Higgs Models
• Search for electroweak production of a vector-like quark decaying to a top quark and a Higgs boson using boosted topologies in fully hadronic final states
• Top-Quark Physics: Status and Prospects
• Search for the Higgs boson produced in association with a $W$ boson and decaying to four $b$-quarks via two spin-zero particles in $pp$ collisions at 13 TeV with the ATLAS detector
• Search for flavour-changing neutral current top quark decays $t\to Hq$ in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector
• Interpreting The 750 GeV Diphoton Excess Within Topflavor Seesaw Model
• LHC constraints on color octet scalars
• Probing TeV scale Top-Philic Resonances with Boosted Top-Tagging at the High Luminosity LHC
• Search for single production of a heavy vector-like T quark decaying to a Higgs boson and a top quark with a lepton and jets in the final state
• Search for single production of vector-like quarks decaying to a Z boson and a top or a bottom quark in proton-proton collisions at sqrt(s) = 13 TeV
• Models of LHC Diphoton Excesses Valid up to the Planck scale
• Threshold enhancement of diphoton resonances
• Search for single production of the heavy vectorlike $T$ quark with $T\to th$ and $h\to \gamma \gamma$ at the high-luminosity LHC
• Constraining top quark flavor violation and dipole moments through three and four top quark productions at the LHC
• Heavy Fermion Bound States for Diphoton Excess at 750GeV $\sim$ Collider and Cosmological Constraints $\sim$
• A new constraint on millicharged dark matter from galaxy clusters
• Search for single production of a vector-like quark via a heavy gluon in the $4b$ final state with the ATLAS detector in $pp$ collisions at $\sqrt{s}=8$ TeV
• Searching for signatures of $E_6$
• The $W\gamma$ decay of the elusive charged Higgs boson in the two-Higgs-doublet model with vectorlike fermions
• Electroweak symmetry breaking and collider signatures in the next-to-minimal composite Higgs model
• Disentangling new physics effects on non-resonant Higgs boson pair production from gluon fusion
• Vector-like Quarks at the Origin of Light Quark Masses and Mixing
• Processes that break baryon number by two units and the Majorana nature of the neutrino
• Search for standard model production of four top quarks in proton-proton collisions at sqrt(s) = 13 TeV
• Top-quark physics at the Large Hadron Collider
• Dark Higgs Channel for FERMI GeV $\gamma$-ray Excess
• Novel Collider and Dark Matter Phenomenology of a Top-philic Z'
• Natural Alignment in the Two Higgs Doublet Model
• The Global Higgs as a Signal for Compositeness at the LHC
• New Physics at 1 TeV?
• Vacuum stability in the Standard Model with vector-like fermions
• Precision QCD Physics at the LHC
• Renormalization Group Constraints on New Top Interactions from Electroweak Precision Data
• A Dark Sector for $g_{\mu }-2$, $R_K$ and a Diphoton Resonance
• Single production of $X_{\pm 5/3}$ and $Y_{\mp 4/3}$ vectorlike quarks at the LHC
• Search for singly produced vector-like top partners in multilepton final states with 139 ${\mathrm{fb}}^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV with the ATLAS detector
• On a reinterpretation of the Higgs field in supersymmetry and a proposal for new quarks
• Partially Natural Two Higgs Doublet Models
• Signatures of top flavour-changing dark matter
• Probing four-fermion operators in the triple top production at future hadron colliders
• Light 't Hooft Top Partners
• ATLAS on-Z Excess Through Vector-Like Quarks
• Diphoton excess from hidden U(1) gauge symmetry with large kinetic mixing
• Minimal Dilaton Model and the Diphoton Excess
• Pseudoscalar decays to gauge bosons at the LHC and at a future 100 TeV collider
• Higgs CP Violation from Vectorlike Quarks
• Probing top-antitop resonances with $t\bar{t}$ scattering at LHC14
• Radiative neutrino models in light of diphoton signals
• Top and bottom partners, Higgs boson on the brane, and the tth signal
• Constraints from Triple Gauge Couplings on Vectorlike Leptons
• Anarchic Yukawas and top partial compositeness: the flavour of a successful marriage
• Effective theory analysis for vector-like quark model
• Collider constraints and new tests of color octet vectors
• Connecting the LHC diphoton excess to the Galatic center gamma-ray excess
• Investigating the jet activity accompanying the production at the LHC of a massive scalar particle decaying into photons
• Soft Gamma Rays from Heavy WIMPs
• Loop induced singlet scalar production through the vector like top quark at future lepton colliders
• Scrutinizing a di-photon resonance at the LHC through Moscow zero
• Rescuing 331 bileptons from the Landau pole
• A search for the first generation charged vector-like leptons at future colliders
• The 750 GeV LHC diphoton excess from a baryon number conserving string model
• Asymmetric Dark Matter in Extended Exo-Higgs Scenarios
• ttH, ttZ and ttW measurements at LHC and top quark compositeness