Search for a light charged Higgs boson in $t\to H^{\pm }b$ decays, with $H^{\pm }\to cb$, in the lepton+jets final state in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

A search for a charged Higgs boson, $H^{\pm }$, produced in top-quark decays, $t\to H^{\pm }b$, is presented. The search targets $H^{\pm }$ decays into a bottom and a charm quark, $H^{\pm }\to cb$. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying $W$ boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing $b$-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy $\sqrt{s}=13$ TeV between 2015 and 2018 with the ATLAS detector at CERN's Large Hadron Collider, amounting to an integrated luminosity of 139 fb${}^{-1}$. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions $\mathcal{B}(t\to H^{\pm }b)\times \mathcal{B}(H^{\pm }\to cb)$ for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.

arXiv comment51 pages in total, author list starting page 34, 8 figures, 3 tables, submitted to JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2019-24/

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• ATLAS searches for additional scalars and exotic Higgs boson decays with the LHC Run 2 dataset
• Search for a light charged Higgs boson in $t\to H^{\pm }b$ decays, with $H^{\pm }\to cs$, in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Search for charged Higgs bosons produced in top-quark decays or in association with top quarks and decaying via $H^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ in 13 TeV $pp$ collisions with the ATLAS detector
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