Editing Cabibbo–Kobayashi–Maskawa matrix (section)

==Observations and predictions==
Cabibbo's idea originated from a need to explain two observed phenomena:
#the transitions {{nowrap| {{math|u ↔ d}}, }} {{nowrap| {{math|e ↔ ν<sub>e</sub>}} ,}} and {{nowrap| {{math|μ ↔ ν<sub>μ</sub>}} }} had similar amplitudes.
#the transitions with change in strangeness {{nowrap| {{math|ΔS {{=}} 1}} }} had amplitudes equal to {{sfrac| 1 |4}} of those with {{nowrap| {{math|ΔS {{=}} 0}} .}}
Cabibbo's solution consisted of postulating ''weak universality'' (see below) to resolve the first issue, along with a mixing angle {{math|''θ''<sub>c</sub>}}, now called the ''Cabibbo angle'', between the {{math|d}} and {{math|s}} quarks to resolve the second.

For two generations of quarks, there can be no CP violating phases, as shown by the counting of the previous section. Since CP violations ''had'' already been seen in 1964, in neutral [[kaon]] decays, the [[standard model (basic details)|Standard Model]] that emerged soon after clearly indicated the existence of a third generation of quarks, as Kobayashi and Maskawa pointed out in 1973. The discovery of the [[bottom quark]] at [[Fermilab]] (by [[Leon Lederman]]'s group) in 1976 therefore immediately started off the search for the [[top quark]], the missing third-generation quark.

Note, however, that the specific values that the angles take on are ''not'' a prediction of the standard model: They are [[free parameter]]s. At present, there is no generally-accepted theory that explains why the angles should have the values that are measured in experiments.