One of the best tests for compositeness of leptons or quarks is the presence of an anomalous magnetic moment $F_2$. We determine limits on $F_2$ for the $\tau$, from $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ at PETRA, of $F_2^{\tau }<~0.02$. We also present limits on the $F_2$ of the quarks. We suggest lower-energy experiments on the angular distribution to give an independent measurement of $F_2^{\tau }$. Future experiments near the $Z^0$ peak are discussed.

• Received 28 October 1982

DOI:https://doi.org/10.1103/PhysRevD.27.1196