Direct determination of the CKM matrix from decays of W Bosons and top quarks at high energy $\mathbf{e}^+\mathbf{e}^-$ colliders

Abstract.

At proposed high energy linear $\mathrm{e}^+\mathrm{e}^-$ colliders a large number of W bosons and top quarks will be produced. We evaluate the potential precision to which the decay branching ratios into the various quark species can be measured, implying also the determination of the respective CKM matrix elements. Crucial is the identification of the individual quark flavours, which can be achieved independent of QCD models. For transitions involving up quarks the accuracy is of the same order of magnitude as has been reached in hadron decays. We estimate that for charm transitions a precision can be reached that is superior to current and projected traditional kinds of measurements. The $\mathrm{t}\to \mathrm{b}$ determination will be significantly improved, and for the first time a direct measurement of the $\mathrm{t}\to \mathrm{s}$ transition can be made. In all cases such a determination is complementary to the traditional way of extracting the CKM matrix elements.