Probing the <i>CP</i> nature of the top-Higgs Yukawa coupling in <i>t</i>(<i>t</i>)over-bar<i>H</i> and <i>tH</i> events with <i>H</i> →<i>b</i>(<i>b</i>)over-bar decays using the ATLAS detector at the LHC

Abstract

<p>The <em>CP</em> properties of the coupling between the <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/higgs-boson" title="Learn more about Higgs boson from ScienceDirect's AI-generated Topic Pages">Higgs boson</a> and the top quark are investigated using 139 fb⁻¹ of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of 𝑠=13 TeV. The <em>CP</em> structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of <em>b</em>-quarks and produced in association with either a pair of top quarks, 𝑡𝑡¯𝐻, or a single top quark, <em>tH</em>. Events containing one or two electrons or <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/muon" title="Learn more about muons from ScienceDirect's AI-generated Topic Pages">muons</a> are used for the measurement. Multivariate techniques are used to select regions enriched in 𝑡𝑡¯𝐻 and <em>tH</em> events, where dedicated <em>CP</em>-sensitive observables are exploited. In an extension of the <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/standard-model" title="Learn more about Standard Model from ScienceDirect's AI-generated Topic Pages">Standard Model</a> (SM) with a <em>CP</em>-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between <em>CP</em>-even and <em>CP</em>-odd couplings is measured to be 𝛼=11−73∘∘+52∘, compatible with the SM prediction corresponding to 𝛼=0.<br></p>