Probing CP-violating top-quark dipole moments with tomographic observables

Abstract

Quantum tomography program reconstructs the full spin density matrix of top-quark pairs from dilepton angular correlations at both electron-positron and hadron colliders. We use symmetry arguments to identify tomographic observables sensitive to CP violation in top quark couplings. As a concrete example, we study the sensitivity of these observables to (chromo-)electric dipole moment operators at the LHC and the FCC-ee. We also construct the optimal observable, which combines tomographic and kinematic information to achieve statistically optimal sensitivity for each operator and production process. The analysis is based on fast detector simulation of top pair production and decay in the dilepton channel. We project a $95\%$ CL sensitivity to new-physics scales (the inverse dipole couplings) of $10-15$ TeV for the electroweak electric dipoles at the FCC-ee ($365$ GeV, $3~{\rm ab}^{-1}$) and of 40 (200) TeV for the top chromo-electric dipole moment at the LHC Run 2 (HL-LHC). This sensitivities exceed those of the traditional observables currently used by experiments to use for these operators, indicating the power of the tomographic approach to search for CP violation.