Search for flavour-changing neutral current top-quark decays t → qZ in proton-proton collisions at √s = 13 TeV with the ATLAS detector

• Autores: Alconada Verzini, María Josefina; Alonso, Francisco; Arduh, Francisco Anuar; Dova, María Teresa; Hoya, Joaquín; Monticelli, Fernando Gabriel; Wahlberg, Hernán Pablo; The ATLAS Collaboration
• Año de publicación: 2018
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas; Física; Hadron-Hadron scattering (experiments)
• Institución: Universidad Nacional de La Plata

A search for flavour-changing neutral-current processes in top-quark decays is presented. Data collected with the ATLAS detector from proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of √s =13 TeV, corresponding to an integrated luminosity of 36.1 fb⁻¹, are analysed. The search is performed using top-quark pair events, with one top quark decaying through the t → qZ (q = u, c) flavour-changing neutral-current channel, and the other through the dominant Standard Model mode t → bW. Only Z boson decays into charged leptons and leptonic W boson decays are considered as signal. Consequently, the final-state topology is characterized by the presence of three isolated charged leptons (electrons or muons), at least two jets, one of the jets originating from a b-quark, and missing transverse momentum from the undetected neutrino. The data are consistent with Standard Model background contributions, and at 95% confidence level the search sets observed (expected) upper limits of 1.7 × 10⁻⁴ (2.4 × 10⁻⁴ on the t → uZ branching ratio and 2.4 × 10⁻⁴ (3.2 × 10⁻⁴) on the t → cZ branching ratio, constituting the most stringent limits to date.
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Facultad de Ciencias Exactas
Instituto de Física La Plata