New Tests for Quark and Lepton Substructure

If quarks and leptons are composite at the energy scale $\Lambda$, the strong forces binding their constituents induce flavor-diagonal contact interactions, which have significant effects at reaction energies well below $\Lambda$. Consideration of their effect on Bhabha scattering produces a new, stronger bound on the scale of electron compositeness: $\Lambda >750\mathrm{}$ GeV. Collider experiments now being planned will be sensitive to $\Lambda \sim 1-5$ TeV for both electrons and light quarks.