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, S. Alderweireldt, J.F. Allen, T.M. Carter, P. J. Clark, J.R. Curran, D. Duda, S. M. Farrington, Y. Gao, J.M. Gargan, R.Y. Gonzalez Andana, C. Jiang, C. Leonidopoulos, M. Firdaus M. Soberi, V. J. Martin, L. Mijović, V.A. Parrish, E.A. Pender, T. Qiu, J.M. SilvaN. Themistokleous, E.M. Villhauer, B.M. Wynne, Z. Xu, E. Zaid

Research output: Contribution to journalArticlepeer-review

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 t ¯t and H t production. For the t ¯t production, one top quark decays via t → H q. 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 → H q branching ratios at 95 % confidence level, amounting to observed (expected) limits of B(t → H u) < 2.8 (3.0) × 10−4 and B(t → H c) < 3.3 (3.8) × 10−4 . Combining this search
with other searches for t H q flavour-changing neutral-current interactions previously conducted by ATLAS, considering H → b ¯b and H → γ γ 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 → H u) < 2.6 (1.8) × 10−4 and B(t → H c) <
3.4 (2.3) × 10−4 .
Original languageEnglish
Article number757
Pages (from-to)1-42
Number of pages42
JournalThe European Physical Journal C
Volume84
Issue number7
DOIs
Publication statusPublished - 29 Jul 2024

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