Effects of Higgs sector CP violation in top quark pair production at the LHC

A striking manifestation of CP violation in the electroweak symmetry breaking sector would be the existence of neutral Higgs boson(s) with undefined CP parity. We analyse signatures of such a boson, with a mass of about 300 GeV or larger, produced in high energy proton-proton collisions at LHC energies in its top-quark antitop-quark decay channel. The large irreducible tt background is taken into account. We propose, both for the dilepton and the lepton + jets decay channels of tt, several correlations and asymmetries with which (Higgs sector) CP violation can be traced. We show that for judiciously chosen cuts on the tt invariant mass these CP observables yield, for an LHC integrated luminosity of 100 fb, statistically significant signals for a range of Higgs boson masses and Yukawa couplings. PACS number(s): 11.30.Er, 12.60.Fr, 14.65.Ha, 14.80.Cp