2025/10/27 by Atlas Collaboration, G. Aad, Erlend Aakvaag +194
Physics and Astronomy · #Particle physics theoretical and experimental studies #High-Energy Particle Collisions Research #Neutrino Physics Research
paper · pdf · doi:10.1007/jhep05(2026)183
A bstract A measurement of the associated production of a top-quark pair with the Higgs boson ( ttH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:math> ) in multilepton final states is presented. The analysis is based on a data sample of proton-proton collisions at √(s)=13 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> </mml:math> TeV recorded with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 140 fb − 1 . Six final states defined by the number and flavour of reconstructed charged leptons are combined in a simultaneous likelihood fit to extract the ttH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:math> signal and constrain the most relevant backgrounds. The measured ttH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:math> cross-section normalised to Standard Model (SM) prediction is σ_ttH/σSM=0.63-0.19+0.20 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mrow> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:msup> <mml:mi>σ</mml:mi> <mml:mi>SM</mml:mi> </mml:msup> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>63</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.20</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . This result corresponds to an observed (expected) significance of 3.3 σ (5.3 σ ). Additionally, two other fits are used to measure the ttH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:math> cross-section differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, and to extract the associated production cross-section of a single top-quark with the Higgs boson ( tH ) together with the ttH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:math> one. The CP structure of the top quark-Higgs boson Yukawa coupling is probed through an analysis of ttH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:math> and tH events. The results are compatible with the SM hypothesis, and values of the mixing angle between CP -even and CP -odd top-Higgs Yukawa couplings of | α | > 62 ° are excluded at 68% confidence level.