Search for top-quark decays tHq with 36 fb−1 of pp collision data at √s = 13 TeV with the ATLAS detector

The ATLAS collaboration

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Abstract

A search for flavour-changing neutral current decays of a top quark into an up-type quark (q = u, c) and the Standard Model Higgs boson, tHq, is presented. The search is based on a dataset of pp collisions at √s = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 36.1 fb−1. Two complementary analyses are performed to search for top-quark pair events in which one top quark decays into Wb and the other top quark decays into Hq, and target the Hbb¯ and Hτ+τ decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying τ-leptons, is exploited in the two analyses respectively. Multivariate techniques are used to separate the signal from the background, which is dominated by top-quark pair production. No significant excess of events above the background expectation is found, and 95% CL upper limits on the tHq branching ratios are derived. The combination of these searches with ATLAS searches in diphoton and multilepton final states yields observed (expected) 95% CL upper limits on the tHc and tHu branching ratios of 1.1 × 10−3 (8.3 × 10−4) and 1.2 × 10−3 (8.3 × 10−4), respectively. The corresponding combined observed (expected) upper limits on the |λtcH| and |λtuH| couplings are 0.064 (0.055) and 0.066 (0.055), respectively.

Original languageEnglish
Article number123
Pages (from-to)1-66
Number of pages67
JournalJournal of High Energy Physics
Volume2019
Issue number5
DOIs
Publication statusPublished - May 2019
Externally publishedYes

Bibliographical note

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Keywords

  • Hadron-Hadron scattering (experiments)
  • Rare decay
  • Top physics

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