CP-violation, asymmetries and interferences in $\textit{t}$$\overline{t}\phi$

In this paper, we use the associated production of top-quark pairs ($\overline{tt}$) with a generic scalar boson ($\phi$) at the LHC (pp → $\textit{t}$$\overline{t}\phi$) to explore the sensitivity of a large set of observables to the sign of the CP mixing angle ($\alpha$), present in the coupling between the scalar boson and the top quarks. The mass of the scalar boson is set to m$_{\phi}$ = 125 GeV (the Standard Model Higgs boson mass) and its coupling to top-quarks is varied such that $\alpha$ = 0°, 22.5°, 45.0°, 67.5°, 90.0°, 135.0° and 180.0°. Dileptonic final states of the $\textit{t}$$\overline{t}\phi$ system are used (pp → bℓ$^{+}$ν$_{ℓ}$$\overline{b}$ℓ−$\overline{ν}$$_{ℓ}$b$\overline{b}$), where the scalar boson is expected to decay according to $\phi$ → b$\overline{b}$. A new method to reconstruct the scalar mass, originally designed for the low mass regime is used, improving the resolution of the Higgs mass by roughly a factor of two. A full phenomenological analysis is performed using Standard Model (SM) background and signal events generated with MadGraph5_aMC@NLO, in turn reconstructed using a kinematical fit. The most sensitive CP-observables are selected to compute Confidence Level (CL) limits as a function of the sign of the top quark Yukawa couplings to the $\phi$ boson. ... mehrWe also explore the sensitivity to interference terms using differential distributions and angular asymmetries. Given the significant difference between the pure scalar (σ$_{0+}$) and pure pseudo-scalar (σ$_{0−}$) production cross section values, it is unlikely the $\textit{t}$$\overline{t}\phi$ channel alone will be sensitive to the sign of the CP-mixing angle or interference terms, even at the end of the LHC. Using the b$_{2}$$^{\textit{t}\overline{t}\phi}$ and b$_{4}$$^{\textit{t}\overline{t}\phi}$ variables, exclusion limits at 95% CL for the CP-even and CP-odd components of the top quark Yukawa couplings are expected to be set to $\tilde{κ}$ ∈ [-0.698,+0.698] and |κ| ∈ [0.878,1.04], respectively, at the end of the High Luminosity phase of the LHC (HL-LHC) by using the dileptonic decay channel alone.