CPviolation in top-quark pair production at a Next Linear Collider

Abstract

We provide a detailed, model-independent study for CP-violation effects due to the T-odd top-quark electric dipole moment ͑EDM͒ and weak dipole moment ͑WDM͒ in top-quark pair production via e ϩ e Ϫ and twophoton annihilation at a Next e ϩ e Ϫ Linear Collider ͑NLC͒. There are two methods in detecting 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 CP-odd polarization asymmetry effects of the initial states. In the e ϩ e Ϫ case only the first method can be used and in the ␥␥ case both methods can be employed. We provide a complete classification of angular correlations of the t and t decay products under CP and CP T, which greatly faciliate CP tests in the e ϩ e Ϫ 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 CP-odd and CP T-even initial polarization configurations and apply them to investigating CP-violating effects due to the top-quark EDM. With a typical set of experimental parameters at the NLC, we compare the 1 sensitivities to the top-quark EDM and WDM in the e ϩ e Ϫ mode and the two-photon mode. Some model expectation values of the T-odd parameters are compared with the results.

CP violation in top physics

“…The CP-odd T N -odd distribution ℑm (Σ 00 ) defined in Eq. 9.9 depends linearly on d γ t and is given by [171]: 20) and the asymmetry A 00 defined in Eq. 9.14 can then be calculated [171,233].…”

“…9.9 depends linearly on d γ t and is given by [171]: 20) and the asymmetry A 00 defined in Eq. 9.14 can then be calculated [171,233]. After extracting the top EDM from A 00 and defining A 00 ≡ ℜe (κ γ )Ã 00 , whereκ γ ≡ 2m t d γ t /e is a dimensionless EDM form factor, as in Eq.…”

“…9.1, obtained for combinations such as λ 2 = λ 1 = λ γ or λ 2 = −λ 1 = λ γ and λt = λ t or λt = −λ t , are given by [171,233,234]: 19) where θ t is the scattering angle in the c.m. frame and β t is the top quark velocity and C t = e 2 Q 2 t /(1 − β 2 t cos 2 θ t ).…”

“…If the incoming photons are polarized, then one can construct CP-odd correlations by using linearly polarized photons where no information on the momenta and polarization of the top quark decay products are needed. The amplitude squared for a general final state X, i.e., γγ → X, in the case where the two photons are linearly polarized is given by [171]:…”

“…Here η,η are the degrees of linear polarization of the two initial photons, χ and φ are the azimuthal angle difference and sum, respectively, and the invariant functions are defined as [171]:…”