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



Aaboud, M, Aad, G, Abbott, B, Abdinov, O, Abeloos, B, Abhayasinghe, DK, Abidi, SH, AbouZeid, OS, Abraham, NL, Abramowicz, H
et al (show 2911 more authors) (2019) Search for top-quark decays t → Hq with 36 fb<SUP>-1</SUP> of pp collision data at √s=13 TeV with the ATLAS detector. JOURNAL OF HIGH ENERGY PHYSICS, 05 (5). 123-.

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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, $t\rightarrow Hq$, is presented. The search is based on a dataset of $pp$ collisions at $\sqrt{s}=13$ TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb$^{-1}$. Two complementary analyses are performed that 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 $H\rightarrow b\bar{b}$ and $H\rightarrow\tau^+\tau^-$ decay modes, respectively. The high multiplicity of $b$-quark jets, or the presence of hadronically decaying $\tau$-leptons, are 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 $t\rightarrow Hq$ 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 $t\rightarrow Hc$ and $t\rightarrow Hu$ branching ratios of $1.1 \times 10^{-3}$ ($8.3 \times 10^{-4}$) and $1.2 \times 10^{-3}$ ($8.3 \times 10^{-4}$), respectively. The corresponding combined observed (expected) upper limits on the $|\lambda_{tcH}|$ and $|\lambda_{tuH}|$ couplings are 0.064 (0.055) and 0.066 (0.055), respectively.

Item Type: Article
Additional Information: 68 pages in total, author list starting page 52, 15 figures, 9 tables, published in JHEP, JHEP 05 (2019) 123. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2017-07
Uncontrolled Keywords: Hadron-Hadron scattering (experiments), Rare decay, Top physics
Depositing User: Symplectic Admin
Date Deposited: 14 Jun 2019 10:49
Last Modified: 11 Oct 2023 06:28
DOI: 10.1007/JHEP05(2019)123
Open Access URL: https://link.springer.com/article/10.1007/JHEP05(2...
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3045830