Muon pairs with invariant pair mass $M_{\mu \mu }$ between 1300 and 2100 MeV have been photoproduced from carbon. No evidence is found for a heavy vector boson decaying into muon pairs in this mass region, and upper limits on its production are given. Limits on a possible breakdown of quantum electrodynamics are also obtained. Assuming a breakdown in the cross section proportional to ${M_{\mu \mu }}^4$, we obtain an upper limit on the breakdown parameter $\lambda$ of $\left|\lambda \right|<\mathrm{}0.035\mathrm{}$ Ge${\mathrm{V}}^{-4\mathrm{}}$, with a confidence level of 95%.

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