Explaining excesses in four-leptons at the LHC with a double peak from a CP violating Two Higgs Doublet Model

Abstract

Extended scalar sectors with additional degrees of freedom appear in many scenarios beyond the Standard Model. Heavy scalar resonances that interact with the neutral current could be discovered via broad resonances in the tails of the four-lepton invariant mass spectrum, where the Standard Model background is small and well understood. In this article we consider a recent ATLAS measurement of four-lepton final states, where the data is in excess over the background for invariant masses above 500 GeV. We discuss the possibility that this excess could be interpreted as a "double peak" from the two extra heavy neutral scalars of a CP violating Two Higgs Doublet Model, both coupling to the $Z$ boson. We apply an iterative fitting procedure to find viable model parameters that can match the excess, resulting in a benchmark point where the observed four-lepton invariant mass spectrum can be explained by two scalar particles $H_2$ and $H_3$, with masses of 540 GeV and 631 GeV, respectively, being admixtures of the CP eigenstates. Our explanation predicts additional production processes for $t\bar t$, $W^+W^-$, $4b$ and $\gamma\gamma$, some of which have cross sections close to the current experimental limits. Our results further imply that the electric dipole moment of the electron should be close to the present bounds.