Cabibbo–Kobayashi–Maskawa matrix

The unitary matrix that relates down-type quark mass eigenstates to the combinations that participate in charged weak interactions. Its complex phase permits CP violation in the Standard Model.

Quark mixing: The mismatch between quark mass eigenstates and the states coupled by charged weak interactions. The matrix gives the quantitative description of this mismatch.
Quark: A quark is an elementary fermion that carries color charge and participates in the strong interaction. The matrix acts on the three down-type quark flavors.
Nicola Cabibbo: Nicola Cabibbo was an Italian physicist who introduced quark mixing to describe weak decays in 1963. His single-angle proposal became the two-generation starting point for the matrix.
B meson: A B meson is a bound state containing a bottom quark or antiquark and a light quark or antiquark. B-meson decays provide sensitive measurements of several matrix elements and phases.
Pontecorvo–Maki–Nakagawa–Sakata matrix: The Pontecorvo–Maki–Nakagawa–Sakata matrix describes mixing among neutrino flavors in charged weak interactions. It is the lepton-sector counterpart, with neutrino mixing rather than quark mixing.
W and Z bosons: The W and Z bosons are the massive carriers of the weak interaction. W-boson vertices contain the matrix elements that mediate quark flavor changes.
Quark flavor: Quark flavor identifies one of six quark types: up, down, charm, strange, top, or bottom. Its rows and columns distinguish up-type and down-type flavors.
Cabibbo angle: The Cabibbo angle parameterizes mixing between the down and strange quarks in a two-generation description. It is the original mixing angle generalized by the three-generation matrix.
Kaon: A kaon is a meson containing a strange quark or antiquark. Kaon decays constrain matrix elements involving strange and down quarks.
Flavor-changing neutral current: A flavor-changing neutral current changes fermion flavor without changing electric charge. The CKM matrix governs charged-current mixing, while neutral flavor changes are suppressed in the Standard Model.

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