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Search for top-quark decays t ? Hq with 36 fb-1 of pp collision data at sv = 13 TeV with the ATLAS detector

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journal contribution
posted on 2023-06-09, 18:44 authored by N L Abraham, Benedict AllbrookeBenedict Allbrooke, Lily AsquithLily Asquith, Alessandro CerriAlessandro Cerri, Batool Safarzadeh Samani, Antonella De SantoAntonella De Santo, Fabrizio SalvatoreFabrizio Salvatore, Kate ShawKate Shaw, Thomas StevensonThomas Stevenson, K Suruliz, Mark SuttonMark Sutton, Iacopo Vivarelli, The ATLAS collaboration, others
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 sv = 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 ? t+t- decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying t-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 |?tcH| and |?tuH| couplings are 0.064 (0.055) and 0.066 (0.055), respectively.


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Journal of High Energy Physics




Institute of Physics





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