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 $\ensuremath{\Lambda}>1260$ and $\ensuremath{\Lambda}>750$ MeV, respectively (15 times the mass limits of positronium experiments). A model used to calculate $\ensuremath{\rho}\ensuremath{-}\mathrm{Q}\mathrm{E}\mathrm{D}$ interference yields a best $\ensuremath{\rho}\ensuremath{-}\mathrm{Q}\mathrm{E}\mathrm{D}$ phase angle of 16\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}22\ifmmode^\circ\else\textdegree\fi{}.