Abstract
We study the potential of future lepton colliders to probe violation of the CP symmetry in the top quark sector. In certain extensions of the Standard Model, such as the two-Higgs-doublet model (2HDM), sizeable anomalous top quark dipole moments can arise, which may be revealed by a precise measurement of top quark pair production. We present results from detailed Monte Carlo studies for the ILC at 500 hbox { GeV} and CLIC at 380 hbox { GeV} and use parton-level simulations to explore the potential of high-energy operation. We find that precise measurements in e^+e^- rightarrow tbar{t} production with subsequent decay to lepton plus jets final states can provide sufficient sensitivity to detect Higgs-boson-induced CP violation in a viable two-Higgs-doublet model. The potential of a linear e^+e^- collider to detect CP-violating electric and weak dipole form factors of the top quark exceeds the prospects of the HL-LHC by over an order of magnitude.
Highlights
The top quark is by far the heaviest fundamental particle known to date
In order to estimate the potential size of the top-quark electric dipole form factor (EDF) and weak dipole form factor (WDF), we evaluated the chargino, gluino, and neutralino contributions using the formulae of [41, 42] with SUSY masses that are in accord with these experimental constraints
CP violation in the top-quark sector is relatively unconstrained by direct measurements
Summary
The top quark is by far the heaviest fundamental particle known to date. Its large mass implies that it is the Standard Model particle that is most strongly coupled to the electroweak symmetry breaking sector. The experimental investigation of single top and top-quark pair production at the Tevatron and at the Large Hadron Collider (LHC) has led to a precise knowledge of the top-quark strong and weak charged-current interactions These results are in good agreement with the Standard Model (SM) predictions. Within the two SM extensions that will be discussed, the dXt (s) are gauge-invariant to one-loop approximation This may justify their use in parametrizing possible CP-violating effects in tt production. In parti√cular, in the kinematic domain that we are interested in, dγt and dZt show a non-negligible dependence on s and can develop absorptive parts, becoming complex
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