New Tests for Quark and Lepton Substructure

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