A Search for the Fourth SM Family Fermions and E6 Quarks at μ+μ− Colliders

The mass spectrum and the mixing of fundamental fermions are the most important unsolved problems of the particle physics. According to the Standard Model (SM), these masses and mixings arise from the interaction with the Higgs doublet via spontaneous symmetry breaking. In the framework of SM, fermions with the same quantum numbers (electric charge, weak isospin, etc.) are indistinguishable before the symmetry breaking. Therefore, in the fermion-Higgs interaction, the Lagrangian terms corresponding to fermions with the same