retired,

Particle Physics seeks to identify the elementary consti-tuents of nature and to discover the fundamental forces acting between these constituents. Ordinary matter and non-gra-vitational interactions are described by the Standard Model which comprises two kinds of matter particles (quarks and leptons), three fundamental forces (the strong, electromag-netic and weak interactions) and the Higgs sector as the ori-gin of mass via spontaneous symmetry breaking. The Stan-dard Model constitutes a quantum eld theory valid down to microscopic distances of the order of . The only Standard Model particle that escaped detection so far is the Higgs boson. The search for it is one of the most important endeavours at present and future collider experiments. Quarks and leptons are grouped into three families (see Fig. 1). The rst family contains the electron and the elec