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

Research output: Contribution to journalArticle

  • External authors:
  • Agni Bethani
  • Alexander Bitadze
  • Jonathan Crane
  • Cinzia Da Via
  • Nicholas Dann
  • Sam Dysch
  • Alessandra Forti
  • Emily Hanson
  • James Howarth
  • David Lack
  • Ivan Lopez Paz
  • Jiri Masik
  • Stephen Menary
  • Alexander Oh
  • Joleen Pater
  • Yvonne Peters
  • Rebecca Pickles
  • Yang Qin
  • Jacob Rawling
  • Nicolas Scharmberg
  • Savanna Shaw
  • Terence Wyatt

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, t → Hq, 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 H→bb¯¯ and H → τ+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 t → Hq 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 t → Hc and t → Hu 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.

Bibliographical metadata

Original languageEnglish
JournalThe Journal of High Energy Physics
Early online date21 May 2019
DOIs
Publication statusPublished - 2019