Journal of High Energy Physics > 2019 > 2019 > 5 > 1-67
Search for top-quark decays t → Hq with 36 fb−1 of pp collision data at s $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Source
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 $$ \sqrt{s} $$ = 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 → b b ¯ $$ H\to b\overline{b} $$ 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.
Identifiers
journal e-ISSN : | 1029-8479 |
DOI | 10.1007/JHEP05(2019)123 |
Authors
The ATLAS collaboration
- University Politehnica Bucharest, Bucharest, Romania
- Centre National de l’Energie des Sciences Techniques Nucleaires (CNESTEN), Rabat, Morocco
- Universidade Nova de Lisboa, Dep Física and CEFITEC of Faculdade de Ciências e Tecnologia, Caparica, Portugal
- CERN, Geneva 23, Switzerland
B. Abbott
- University of Oklahoma, Homer L. Dodge Department of Physics and Astronomy, Norman, United States of America