Measurement of $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$: A Test of Electroweak Theories

We use the reaction $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$, in the Mark J detector at the DESY high-energy $e^{+}{e}^{-}$ collider PETRA, to test the standard electroweak theory and find good agreement. We also set limits on the parameters of several extended gauge theories.