Experimental Determination of the Kobayashi-Maskawa Matrix Elements

In the standard elektroweak theory, the charged current is given by $$ {J_{\lambda }} = \left( {{{\bar{\nu }}_e}\,{{\bar{\nu }}_{\mu }}\,{{\bar{\nu }}_r}} \right){\gamma_{\lambda }}\left( {1 - {\gamma_s}} \right)1\left( {\begin{array}{*{20}{c}} e \\ \mu \\ \tau \\ \end{array} } \right) + \left( {\bar{u}\,\bar{c}\,\bar{t}} \right){\gamma_{\lambda }}\left( {1 - {\gamma_s}} \right)v\left( {\begin{array}{*{20}{c}} d \\ s \\ b \\ \end{array} } \right) + h.c. $$ and describes the couplings of the charged vector bosons W ± to the lefthanded leptons and quarks. The unit matrix 1 in the lepton part reflects our present knowledge that emission of a W - by an electron always leads to an electron neutrino, never to a μ or τ neutrino, and that muons and τ-leptons obey the corresponding rule. In the quark sector the rules are different, emission of a W - by a d quark may may result in any of the three charge 2/3 quarks u, c, or t, and the same holds for the s and the b quark. The coupling strengths are however strictly connected to each other, the standard theory requires V to be a unitary matrix.