Scalar mass dependence of angular variables in t t ¯ϕ production

In this paper we explore CP discrimination in the associated production of top-quark pairs (t t ¯) with a generic scalar boson (𝜙) at the LHC. We probe the CP-sensitivity of several observables for a varying scalar boson mass and CP-number, either CP-even (𝜙 = H ) or CP-odd (𝜙 = A), using dileptonic final states of the t t ¯ϕ system, with 𝜙 →b b ¯. We show that CP-searches are virtually impossible for 𝜙 boson masses above a few hundred GeV in this channel. A full phenomenological analysis was performed, using Standard Model background and signal events generated with MadGraph5_aMC@NLO and reconstructed using a kinematic fit. The most sensitive CP-observables are used to compute Confidence Levels (CLs), as a function of luminosity, for the exclusion of different signal hypotheses with scalar and pseudoscalar boson masses that range from m_𝜙 = 40 GeV up to 200 GeV. We finalize by analysing the impact of a measurement (or limit) of the CP-violating angle in the parameter space of a complex two-Higgs doublet model known as the C2HDM.