Searches for lepton-flavour-violating decays of the Higgs boson into $e\tau$ and $\mu \tau$ in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

Abstract

This paper presents direct searches for lepton flavour violation in Higgs boson decays, $H\to e\tau$ and $H\to \mu \tau$, performed using data collected with the ATLAS detector at the LHC. The searches are based on a data sample of proton-proton collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 138 fb${}^{-1}$. Leptonic ($\tau \to \ell {\nu }_{\ell }{\nu }_{\tau }$) and hadronic ($\tau \to$ hadrons ${\nu }_{\tau }$) decays of the $\tau$-lepton are considered. Two background estimation techniques are employed: the MC-template method, based on data-corrected simulation samples, and the Symmetry method, based on exploiting the symmetry between electrons and muons in the Standard Model backgrounds. No significant excess of events is observed and the results are interpreted as upper limits on lepton-flavour-violating branching ratios of the Higgs boson. The observed (expected) upper limits set on the branching ratios at 95% confidence level, $\mathcal{B}(H\to e\tau )<0.20\%$ (0.12%) and $\mathcal{B}(H\to \mu \tau )<0.18\%$ (0.09%), are obtained with the MC-template method from a simultaneous measurement of potential $H\to e\tau$ and $H\to \mu \tau$ signals. The best-fit branching ratio difference, $\mathcal{B}(H\to \mu \tau )-\mathcal{B}(H\to e\tau )$, measured with the Symmetry method in the channel where the $\tau$-lepton decays to leptons, is (0.25 $\pm$ 0.10)%, compatible with a value of zero within 2.5$\sigma$.

arXiv comment71 pages in total, author list starting on page 54, 16 figures, 13 tables, published in JHEP 07 (2023) 166. All figures including auxiliary material are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2019-11

References in corpus (44)

• 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
• A Brief Introduction to PYTHIA 8.1
• FastJet user manual
• New Generation of Parton Distributions with Uncertainties from Global QCD Analysis
• 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
• New parton distributions for collider physics
• Herwig++ Physics and Manual
• Parton distributions with LHC data
• PDF4LHC recommendations for LHC Run II
• Parton distributions in the LHC era: MMHT 2014 PDFs
• 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
• Event Generation with Sherpa 2.2
• Non-Abelian Discrete Symmetries in Particle Physics
• Flavor Violating Higgs Decays
• NLO matrix elements and truncated showers
• Higgs boson production in association with top quarks in the POWHEG BOX
• Matching Tree-Level Matrix Elements with Interleaved Showers
• Flavour-Changing Decays of a 125 GeV Higgs-like Particle
• A New Mass Reconstruction Technique for Resonances Decaying to di-tau
• Handbook of LHC Higgs Cross Sections: 3. Higgs Properties
• Probing lepton flavour violation with Higgs boson decays H-> li+lj
• Higgs Mediated FCNC's in Warped Extra Dimensions
• Natural Neutrino Masses and Mixings from Warped Geometry
• Composite Higgs-Mediated FCNC
• Flavour Changing Higgs Couplings in a Class of Two Higgs Doublet Models
• Higgs-induced lepton flavor violation
• Modified Higgs branching ratios versus CP and lepton flavor violation
• NLO QCD corrections to ZZ+jet production at hadron colliders
• Electroweak and Flavour Structure of a Warped Extra Dimension with Custodial Protection
• Lepton Flavor and Non-Universality from Minimal Composite Higgs Setups
• LHCb anomaly and $B$ physics in flavored Z${}^{\prime }$ models with flavored Higgs doublets
• Comprehensive Analysis on Lepton Flavor Violating Higgs Boson to mu tau Decay in Supersymmetry without R Parity
• Non-decoupling SUSY in LFV Higgs decays: a window to new physics at the LHC
• Asymmetric lepton-flavor violating Higgs decays
• LHC sensitivity to lepton flavour violating Z boson decays
• Studying W+W- production at the Fermilab Tevatron with SHERPA

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