Search for a new scalar resonance in flavour-changing neutral-current top-quark decays $t\to qX$ ($q=u,c$), with $X\to b\bar{b}$, in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle $X$ decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to $qX$, with $X\to b\bar{b}$, and the other top quark decays according to the Standard Model, with the $W$ boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from $b$-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb${}^{-1}$ of proton-proton collisions at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction $\mathcal{B}$($t\to uX$) and between 0.018% and 0.078% for the branching fraction $\mathcal{B}$($t\to cX$), for masses of the scalar particle $X$ between 20 and 160 GeV.

arXiv comment50 pages in total, 9 figures, 5 tables. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2020-16/

References in corpus (55)

• The anti-k_t jet clustering algorithm
• An Introduction to PYTHIA 8.2
• A Brief Introduction to PYTHIA 8.1
• FastJet user manual
• Asymptotic formulae for likelihood-based tests of new physics
• A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX
• A New Method for Combining NLO QCD with Shower Monte Carlo Algorithms
• Matching NLO QCD computations with Parton Shower simulations: the POWHEG method
• Parton distributions for the LHC Run II
• Herwig++ Physics and Manual
• Confidence Level Computation for Combining Searches with Small Statistics
• PDF4LHC recommendations for LHC Run II
• The total top quark pair production cross-section at hadron colliders through O(alpha_S^4)
• Scattering Amplitudes with Open Loops
• Top++: a program for the calculation of the top-pair cross-section at hadron colliders
• Herwig 7.0 / Herwig++ 3.0 Release Note
• A parton shower algorithm based on Catani-Seymour dipole factorisation
• QCD Matrix Elements + Parton Showers
• Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions
• An update on vector boson pair production at hadron colliders
• Comix, a new matrix element generator
• Event Generation with Sherpa 2.2
• QCD matrix elements + parton showers: The NLO case
• High-precision QCD at hadron colliders: electroweak gauge boson rapidity distributions at NNLO
• Two-loop soft anomalous dimensions for single top quark associated production with a W- or H-
• QCD matrix elements and truncated showers
• Collier: a fortran-based Complex One-Loop LIbrary in Extended Regularizations
• -- HATHOR -- HAdronic Top and Heavy quarks crOss section calculatoR
• Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations
• Single-top hadroproduction in association with a W boson
• Percent level precision physics at the Tevatron: first genuine NNLO QCD corrections to q qbar -> t tbar + X
• Top-pair production at hadron colliders with next-to-next-to-leading logarithmic soft-gluon resummation
• NNLO corrections to top-pair production at hadron colliders: the all-fermionic scattering channels
• NNLO corrections to top pair production at hadron colliders: the quark-gluon reaction
• A critical appraisal of NLO+PS matching methods
• OpenLoops 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
• HATHOR for single top-quark production: Updated predictions and uncertainty estimates for single top-quark production in hadronic collisions
• Single-top t-channel hadroproduction in the four-flavour scheme with POWHEG and aMC@NLO
• Angular correlations of lepton pairs from vector boson and top quark decays in Monte Carlo simulations
• Parameterized Machine Learning for High-Energy Physics
• Effects of mixing with quark singlets
• FCNC top quark decay in the MSSM: a door to SUSY physics in high luminosity colliders?
• b-Initiated processes at the LHC: a reappraisal
• Operation of the ATLAS trigger system in Run 2
• SUSY-induced FCNC top-quark processes at the Large Hadron Collider
• Top-quark rare decay $t\to ch$ in R-parity-violating SUSY
• Loop Induced Flavor Changing Neutral Decays of the Top Quark in a General Two-Higgs-Doublet Model
• Reweighting QCD matrix-element and parton-shower calculations
• New NLOPS predictions for $\mathbf{t}\bar{\mathbf{t}}+\mathbf{b}$-jet production at the LHC
• Automatic computations at next-to-leading order in QCD for top-quark flavor-changing neutral processes
• SUSY induced top quark FCNC decay $t\to ch$ after Run I of LHC
• On the Flavor Structure of Natural Composite Higgs Models & Top Flavor Violation
• Top quark FCNCs in extended Higgs sectors

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