The unitarity triangle
The Standard Model of particle physics accommodates CP violation via a single imaginary quantity called η. This is the imaginary part of the complex number ρ + iη, which determines the strengths of the interactions between the heaviest quarks and the lightest quarks relative to the strengths of the other inter-quark couplings. It is represented as a point (ρ, η) on the complex plane. Along with the origin and the point (1, 0), this defines a "unitarity" triangle. The height of the triangle, η, is the fundamental measure of CP violation in the Standard Model, and the internal angles of the triangle - α, β and γ - determine the magnitudes of various CP-violating asymmetries in B-meson decays.