Top electroweak couplings study at the ILC

The top-quark electroweak couplings are expected to be strongly coupled to the mechanism of electroweak symmetry breaking and thus to be good probes for physics beyond the Standard Model. Currently these couplings can be measured only at hadron colliders, while a previous study shows an $e^+e^-$ collider with beam polarizations, namely ILC, can improve the measurement accuracy which allows to probe new physics models. In order to extend the previous study at the ILC, we develop a new method to measure $t\bar{t}Z/\gamma$ couplings using all kinematic information of the di-leptonic final state from the top-quark pair production. We assume the center-of-mass energy of $500$ GeV, two different beam polarization setups, $(P_{e^-}, P_{e^+}) = (-0.8, +0.3), (+0.8, -0.3)$, and the integrated luminosity of 250 fb$^{-1}$ for each beam polarization. The conventional method, which is also used in the previous study, measures the total cross section and the forward-backward asymmetry. On the other hand, the method developed in this study measures all reconstructed angular information of the final state particles. We found that this new method can improve the measurement accuracy of the couplings by order of 10 %, up to 40 %, compared to the previous study at the ILC.