Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb${}^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS experiment

Abstract

A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb${}^{-1}$ of proton-proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a $b$-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the $tq\gamma$ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tu\gamma$ coupling of 36 fb (78 fb) and on the branching ratio for $t\to \gamma u$ of $2.8\times 10^{-5}$ ($6.1\times 10^{-5}$). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC $t\gamma$ production via a left-handed (right-handed) $tc\gamma$ coupling of 40 fb (33 fb) and on the branching ratio for $t\to \gamma c$ of $22\times 10^{-5}$ ($18\times 10^{-5}$).

arXiv comment34 pages in total, author list starting page 18, 2 figures, 2 tables, published in Phys. Lett. B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2018-22

References in corpus (58)

• Adam: A Method for Stochastic Optimization
• Scikit-learn: Machine Learning in Python
• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• The anti-k_t jet clustering algorithm
• An Introduction to PYTHIA 8.2
• FastJet user manual
• 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
• Dimension-Six Terms in the Standard Model Lagrangian
• Event generation with SHERPA 1.1
• Herwig++ Physics and Manual
• Parton distributions with LHC data
• The ATLAS Simulation Infrastructure
• PDF4LHC recommendations for LHC Run II
• Parton distributions in the LHC era: MMHT 2014 PDFs
• 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
• A Positive-Weight Next-to-Leading-Order Monte Carlo for Heavy Flavour Hadroproduction
• Comix, a new matrix element generator
• 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-
• QCD matrix elements and truncated showers
• Single-top hadroproduction in association with a W boson
• Muon reconstruction performance of the ATLAS detector in proton--proton collision data at $\sqrt{s}$=13 TeV
• NLO single-top production matched with shower in POWHEG: s- and t-channel contributions
• Next-to-next-to-leading-order collinear and soft gluon corrections for t-channel single top quark production
• Topological cell clustering in the ATLAS calorimeters and its performance in LHC Run 1
• The CT10 NNLO Global Analysis of QCD
• NNLL resummation for s-channel single top quark production
• Performance of pile-up mitigation techniques for jets in $pp$ collisions at $\sqrt{s}=8$ TeV using the ATLAS detector
• Uncertainties on alpha_S in global PDF analyses and implications for predicted hadronic cross sections
• Electron and photon performance measurements with the ATLAS detector using the 2015-2017 LHC proton-proton collision data
• The PDF4LHC Working Group Interim Recommendations
• ATLAS $b$-jet identification performance and efficiency measurement with $t\bar{t}$ events in $pp$ collisions at $\sqrt{s}=13$ TeV
• Jet energy scale measurements and their systematic uncertainties in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• A minimal set of top anomalous couplings
• Phenomenology of Two Higgs Doublet Models with Flavor Changing Neutral Currents
• Performance of missing transverse momentum reconstruction with the ATLAS detector using proton-proton collisions at $\sqrt{s}$ = 13 TeV
• NLO matrix elements and truncated showers
• Single-top t-channel hadroproduction in the four-flavour scheme with POWHEG and aMC@NLO
• A global approach to top-quark flavor-changing interactions
• Flavor-changing Top Quark Decays In R-Parity Violating SUSY
• Measurements of $b$-jet tagging efficiency with the ATLAS detector using $t\bar{t}$ events at $\sqrt{s}=13$ TeV
• QCD corrections to top quark pair production in association with a photon at hadron colliders
• Measurement of the photon identification efficiencies with the ATLAS detector using LHC Run 2 data collected in 2015 and 2016
• Measurement of the cross-section for W boson production in association with b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
• Automatic computations at next-to-leading order in QCD for top-quark flavor-changing neutral processes
• Measurement of differential production cross-sections for a $Z$ boson in association with $b$-jets in 7 TeV proton-proton collisions with the ATLAS detector
• Search for anomalous single top quark production in association with a photon in pp collisions at sqrt(s) = 8 TeV
• Search for flavour-changing neutral current top-quark decays $t\to qZ$ in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Measurements of the associated production of a Z boson and b jets in pp collisions at sqrt(s) = 8 TeV
• Measurements of inclusive and differential fiducial cross-sections of $t\bar{t}\gamma$ production in leptonic final states at $\sqrt{s}$ = 13 TeV in ATLAS
• Measurement of the production cross section of a W boson in association with two b jets in pp collisions at sqrt(s) = 8 TeV

Cited by in corpus (15)

• Flavor Constraints from Unitarity and Analyticity
• Search for new physics in top quark production with additional leptons in proton-proton collisions at $\sqrt{s}=$ 13 TeV using effective field theory
• Automated EW corrections with isolated photons: $t\bar{t}\gamma$, $t\bar{t}\gamma \gamma$ and $t\gamma j$ as case studies
• Studying the $b\to s{\ell }^{+}{\ell }^{-}$ anomalies and $(g-2{)}_{\mu }$ in $R$-parity violating MSSM framework with the inverse seesaw mechanism
• Rare and exclusive few-body decays of the Higgs, Z, W bosons, and the top quark
• Search for flavour-changing neutral-current couplings between the top quark and the photon with the ATLAS detector at $\sqrt{s}=13$ TeV
• Loop induced top quark FCNC through top quark and dark matter interactions
• Search for a heavy neutral Higgs boson in a left-right model with an inverse seesaw mechanism at the LHC
• Study of interference effects in the search for flavour-changing neutral current interactions involving the top quark and a photon or a $Z$ boson at the LHC
• Probing FCNC couplings in single top quark production associated with a neutral gauge boson at future lepton colliders
• Non-diagonal contributions to $Z\gamma V^{\ast }$ vertex, polarizations and bounds on $Z\overline{t}q$ couplings
• Generic tests of CP-violation in high-$p_{\text{T}}$ multi-lepton signals at the LHC and beyond
• Probing the anomalous tqgamma couplings in photon-proton collisions
• Explicit Soft Supersymmetry Breaking in the Heterotic M-Theory $B-L$ MSSM
• Elastic Potential: A proposal to discover elastic production of top quarks at the Large Hadron Collider