Search for Compositeness in Dilepton Final States at DØ.

We report preliminary results of a search for substructure in quarks and leptons assuming a four-fermion contact interaction for dielectron pairs of large invariant mass. The search is based on dielectron data collected by the DØ detector in $p{\bar p}$ collisions at $\sqrt{s}=1.96~{\rm TeV}$. The results agree well with predictions of the standard model and we obtain model-dependent lower limits at 95% confidence level on the compositeness scale of 3.6 to 9.1 TeV for different chiral models of the composite structure of quarks and electrons. [ABSTRACT FROM AUTHOR]