Measurement of Electroproduction of Muon Pairs

An experiment on electroproduction of muon pairs with invariant masses between 400 and 900 MeV is reported. The experiment, interpreted as a text of the timelike photon propagator, shows agreement with QED. Photon propagator modifications representing (+) metric and (-) metric heavy photons are limited to masses $\Lambda >1260\mathrm{}$ and $\Lambda >750\mathrm{}$ MeV, respectively (15 times the mass limits of positronium experiments). A model used to calculate $\rho -\mathrm{Q}\mathrm{E}\mathrm{D}$ interference yields a best $\rho -\mathrm{Q}\mathrm{E}\mathrm{D}$ phase angle of 16°±22°.