January, 2005 Kowalewski --- Perugia lectures 4 Historical context 1974 was an exciting year for particle physics, with the discovery of the (2 nd generation) charm quark (J/ ψ ) and the (3 rd generation) τ lepton The search for a 3 rd generation of quarks was motivated by symmetry with the lepton sector as well as by the insight of Kobayashi and Maskawa (in 1973) that a 3x3 quark mixing matrix has an irreducible imaginary parameter that can lead to CP violation
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