Measurements of the ρ and η Parameters of theVCKMMatrix and Perspectives

A review of the current status of the Cabibbo–Kobayashi–Maskawa matrix ( V CKM ) is presented and a special emphasis is put on the determination of the ρ and η parameters. From this study it follows that, in the Standard Model, the B s 0 –( B s 0 )bar oscillation frequency, Δ m s , has to lie with 68% C.L., between 6.5ps -1 and 15ps -1 , and is below 21ps -1 at 95% C.L. If the interest of measuring Δ m s is underlined, the importance of a precise determination of the B meson decay constant, f B , is also stressed. It is also proposed to obtain a precise value for this parameter from an accurate measurement of f D , the D meson decay constant, using results from lattice QCD to relate D and B hadrons. A future Tau–Charm factory could accomplish this task. It is also shown that from the present measurements, assuming the validity of the Standard Model, an already accurate value of sin 2β = 0.67 -0.13 +0.12 is obtained. So far no constraint can be obtained on sin 2α. The interest of having a direct measurement of sin 2α and sin 2β at B-factories or at other facilities is reminded. Finally, constraints on SUSY parameters, in the framework of a given model, obtained from a precise measurement of the CKM matrix elements are analyzed.