Glashow, Salama and Weinberg's electroweak interaction theory, which unified electromagnetic interactions and weak interactions, predicted so called weak neutral currents. The processes involving weak neutral currents were first observed by means of Gargamelle bubble chamber in CERN in 1973.
Three quarks of which matter was supposed to be built, as proposed by Gell-Mann and Zweig, seemed too few. It was speculated that for symmetry's sake yet another quark should exist. The first particle containing the new quark called charm c one was the meson named later J/Y. It was discovered in 1974 by two independent teams working in Stanford and New York. J/Y meson was observed during energetic collisions and high energy annihilations of electrons and positrons
Another lepton, called lepton t, which belongs to the third generation of elementary particles, was discovered in Stanford Linear Accelerator Center - SLAC in 1975. Lepton tau is heavier than meson J/Y, it has a very short lifetime. It decays before it can be registered by a detector to electrons and other light particles (muons?) registered in a calorimeter
Beauty quark in system beauty-antibeauty quarks (bb) creates a particle called Epsilon (T) which was for the first time observed in Fermi National Laboratory (USA) in 1977.