New tests for quark and lepton substructure

If quarks and leptons are composite at the energy scale Λ, the strong forces binding their constituents induce flavor-diagonal contact interactions. Through their interference with standard color electro-weak model amplitudes, these contact interactions can have significant effects at reaction energies well below Λ. Consideration of their effect on Bhabha scattering produces a new stronger bound on the scale of electron compositeness: Λ > 750 GeV. Collider experiments now being planned will be sensitive to Λ approximately 1-5 TeV for both electrons and light quarks. The super-colliders of the next decade will be able to probe up to Λ approximately 10-50 TeV