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Title

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

CollaborationWith : Akilli, Ece / Amrouche, Cherifa Sabrina / Ancu, Lucian Stefan / Benoit, Mathieu / Clark, Allan Geoffrey / Della Volpe, Domenico / Di Bello, Francesco Armando / Dubreuil, Arnaud / Ferrere, Didier / Gadatsch, Stefan / Golling, Tobias / Gonzalez Sevilla, Sergio / Iacobucci, Giuseppe / Iizawa, Tomoya / Jansky, Roland / Khoo, Teng Jian / Kiehn, Moritz / Lanfermann, Marie Christine / Lionti, Anthony Eric / March Ruiz, Luis / Mermod, Philippe / Nessi, Marzio / Nindhito, Herjuno Rah / Paolozzi, Lorenzo / Poggi, Riccardo / Raine, Johnny / Salamani, Dalila / Schramm, Steven / Sfyrla, Anna / Sultan, D M S / Valente, Marco / Vicente Barreto Pinto, Mateus / Wu, Xin / Zaffaroni, Ettore
Published in . 2019, vol. 1905, p. 123
Collection Open Access - SCOAP3
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 → 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 | λ tcH | and | λ tuH | couplings are 0.064 (0.055) and 0.066 (0.055), respectively.
Keywords Hadron-Hadron scattering (experiments)Rare decayTop physics
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arXiv: 1812.11568
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ATLAS COLLABORATION. Search for top-quark decays t → Hq with 36 fb −1 of pp collision data at √s = 13 TeV with the ATLAS detector. In: Journal of High Energy Physics, 2019, vol. 1905, p. 123. doi: 10.1007/JHEP05(2019)123 https://archive-ouverte.unige.ch/unige:118802

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Deposited on : 2019-06-04

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