Search for flavour-changing neutral current couplings between the top quark and the Higgs boson in multilepton final states with the ATLAS detector

TL;DR

This paper reports a search for rare flavor-changing neutral current interactions between the top quark and the Higgs boson using ATLAS data, setting upper limits on their branching ratios in multilepton final states.

Contribution

It provides the first limits on FCNC couplings involving the top quark and Higgs boson in multilepton channels at 13 TeV with 140 fb$^{-1}$ of data.

Findings

Upper limit on $ ext{Br}(t o Hu)$ is $2.8 imes 10^{-4}$

Upper limit on $ ext{Br}(t o Hc)$ is $3.3 imes 10^{-4}$

No significant excess observed over the Standard Model expectations.

Abstract

These proceedings present a search for flavour-changing neutral-current (FCNC) interaction involving the top quark, Higgs boson and either the up or the charm quark, using 140 fb$^{-1}$ of 13 TeV proton--proton collision data from the ATLAS detector at the Large Hadron Collider. Two channels are considered: the production of top quark-antiquark pair with one top decaying via FCNC, and the associated production of a top quark and Higgs boson. Final states contain either two same-charge leptons, or three leptons of which two have the same charge. Observed (expected) upper limits on the branching rations are determined as $\mathcal{B}(t\to Hu)<2.8\,(3.0) \times 10^{-4}$ and $\mathcal{B}(t\to Hc)<3.3\,(3.8) \times 10^{-4}$.