Compositeness limits frome+e−annihilation reexamined

Measurements of lepton pair production cross sections by experiments at the SLAC, DESY, and KEK $e^{+}{e}^{-}$ colliders PEP, PETRA, and TRISTAN are reinvestigated in terms of new contact interactions. For maximum sensitivity, a combined analysis of previous measurements and of different leptonic final states is performed. Possible deviations from the standard model are parametrized by the variable $\varepsilon =\pm {\Lambda }^{-2\mathrm{}}$ which provides a more sensitive test for additional contact interactions than the traditionally quoted lower limits on the compositeness scale $\Lambda$. Difficulties in the interpretation of these limts due to the non-Gaussian behavior of $\Lambda$ are discussed. Different methods for treating correlations due to common normalization errors of the data points are compared and improvements suggested. The sensitivity of the results to correlations between different cross-section measurements is studied.