Abstract

We report results of a study of four-lepton final states produced in e+e− collisions at center-of-mass energies from 50 to 61.4 GeV using the AMY detector at the TRISTAN collider. For the cases where two or three charged tracks are produced at large angles relative to the beam direction, the cross sections agree with QED. However, we observe an excess of e+e−→e+e−μ+μ− events with four tracks at wide angles and with dimuon mass less than 1.0 GeV/c2.