Search for flavour-changing neutral-current couplings between the top quark and the Higgs boson in multi-lepton final states in 13 TeV pp collisions with the ATLAS detector

ATLAS Collaboration, Phil Allport, Adrien Auriol, Panagiotis Bellos, Juraj Bracinik, David Charlton, Andrew Chisholm, Harry Cooke, Aleksandra Dimitrievska, Will George, Laura Gonella, Francesco Gonnella, Chris Hawkes, Stephen Hillier, Karol Krizka, Eric Liu, Josh Lomas, Mihaela Marinescu, Thomas Neep, Paul NewmanKonstantinos Nikolopoulos, Eleni Skorda, Alexis Stampekis, Jurgen Thomas, Paul Thompson, Gov Virdee, Robert Ward, Alan Watson, Miriam Watson, C. Wu

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Abstract

A search is presented for flavour-changing neutral-current interactions involving the top quark, the Higgs boson and an up-type quark (q=u,c) with the ATLAS detector at the Large Hadron Collider. The analysis considers leptonic decays of the top quark along with Higgs boson decays into two W bosons, two Z bosons or a τ+τ pair. It focuses on final states containing either two leptons (electrons or muons) of the same charge or three leptons. The considered processes are tt¯ and Ht production. For the tt¯ production, one top quark decays via t→Hq. The proton-proton collision data set analysed amounts to 140 fb−1 at √s = 13 TeV. No significant excess beyond Standard Model expectations is observed and upper limits are set on the t→Hq branching ratios at 95\% confidence level, amounting to observed (expected) limits of B(t→Hu) < 2.8(3.0) × 10−4 and B(t→Hc) <3.3(3.8) × 10−4. Combining this search with other searches for tHq flavour-changing neutral-current interactions previously conducted by ATLAS, considering H→bb¯ and H→γγ decays, as well as H→τ+τ decays with one or two hadronically decaying τ-leptons, yields observed (expected) upper limits on the branching ratios of B(t→Hu) < 2.6(1.8) × 10−4 and B(t→Hc) < 3.4(2.3) × 10−4.
Original languageEnglish
Article number757
Number of pages42
JournalEuropean Physical Journal C
Volume84
DOIs
Publication statusAccepted/In press - 2 Jul 2024

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