Speaker: Alexander Lind (CNRS & Subatech Nantes)

I will present recent work on an NLO study of the process pp -> ttbar in the 1-Higgs-singlet extension of the S with an additional heavy Higgs boson that mixes with the light Higgs boson.. This process is subject to large interference effects between loop-induced Higgs-mediated amplitudes and QCD continuum background. A reliable modelling of the resulting top-pair invariant-mass shapes requires the inclusion of higher-order QCD corrections. The computation of NLO corrections is exact in all contributions but in the class of non-factorisable two-loop diagrams, included in an approximate way which preserves all infrared singular limits. We present numerical results for several benchmark points with masses in the range 700-3000 GeV considering the production of stable top quarks. We find that the interference dominates the BSM signal yielding sharp dip structures instead of resonance peaks. The significance and excludability of the BSM effect is explored for the LHC Run 2, Run 3 and HL-LHC.