<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>CP</mml:mi></mml:math>violation in top-quark pair production at a Next Linear Collider

Abstract

We provide a detailed, model-independent study for $\mathrm{CP}$-violation effects due to the $T$-odd top-quark electric dipole moment (EDM) and weak dipole moment (WDM) in top-quark pair production via ${e}^{+}{e}^{\ensuremath{-}}$ and two-photon annihilation at a Next ${e}^{+}{e}^{\ensuremath{-}}$ Linear Collider (NLC). There are two methods in detecting $\mathrm{CP}$-violation effects in these processes. One method makes use of measurements of various spin correlations in the final decay products of the produced top-quark pair, while the other is to measure various $\mathrm{CP}$-odd polarization asymmetry effects of the initial states. In the ${e}^{+}{e}^{\ensuremath{-}}$ case only the first method can be used and in the $\ensuremath{\gamma}\ensuremath{\gamma}$ case both methods can be employed. We provide a complete classification of angular correlations of the $t$ and $\overline{t}$ decay products under $\mathrm{CP}$ and $\mathrm{CP}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{T}$, which greatly faciliate $\mathrm{CP}$ tests in the ${e}^{+}{e}^{\ensuremath{-}}$ mode. Concentrating on the second method with the Compton backscattered high-energetic laser light off the electron or positron beam in the two-photon mode, we construct two $\mathrm{CP}$-odd and $\mathrm{CP}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{T}$-even initial polarization configurations and apply them to investigating $\mathrm{CP}$-violating effects due to the top-quark EDM. With a typical set of experimental parameters at the NLC, we compare the $1\ensuremath{\sigma}$ sensitivities to the top-quark EDM and WDM in the ${e}^{+}{e}^{\ensuremath{-}}$ mode and the two-photon mode. Some model expectation values of the $T$-odd parameters are compared with the results.