Probing CP violation in gamma gamma -->W+W- with polarized photon beams.

Abstract

We demonstrate in a general framework that polarized photons by backscattered laser beams of adjustable frequencies at a TeV linear ${e}^{+}{e}^{\ensuremath{-}}$ collider provide us with a very efficient mechanism to probe $\mathrm{CP}$ violation in two-photon collisions. $\mathrm{CP}$ violation in the process $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{W}^{+}{W}^{\ensuremath{-}}$ is investigated in detail with linearly polarized photon beams. There are two useful $\mathrm{CP}$-odd asymmetries that do not require detailed information on $W$ decay products. The sensitivity to the $\mathrm{CP}$-odd form factors are studied quantitatively by assuming a perfect $e\ensuremath{-}\ensuremath{\gamma}$ conversion and the 20 ${\mathrm{fb}}^{\ensuremath{-}1}$ ${e}^{+}{e}^{\ensuremath{-}}$ integrated luminosity at the ${e}^{+}{e}^{\ensuremath{-}}$ c.m. energies $\sqrt{s}=0.5 \mathrm{and} 1.0$ TeV. The sensitivity is so high that such experiments will allow us to probe new $\mathrm{CP}$ violation effects beyond the limits from some specific models with reasonable physics assumptions. We find that a counting experiment of ${W}^{+}{W}^{\ensuremath{-}}$ events in the two-photon mode with adjustable laser frequencies can have much stronger sensitivity to the $\mathrm{CP}$-odd $\ensuremath{\gamma}(\ensuremath{\gamma})WW$ form factors than can a ${W}^{+}{W}^{\ensuremath{-}}$ decay-correlation experiment with a perfect detector achieve in the ${e}^{+}{e}^{\ensuremath{-}}$ mode.