A search for. mu. yields e. gamma. at the level of 10 sup minus 13

The MEGA -experiment is a search for the decay {mu} {yields} {gamma}, for which the present upper limit for the branching ratio is 4.9 {times} 10{sup {minus}11}. The observation of this decay would indicate the existence of physics outside the standard model of electroweak interactions. The experiment employs highly modular, fast detectors, state-of-the-art electronics, and a staged trigger with on-line filters. The detectors are contained in a 1.5 T solenoidal field produced by a superconducting magnet. Positrons axe confined to the central region and axe measured by a set of thin MWPCs with a designed energy resolution of 350 keV FWHM and angular resolution of 1 deg FWHM. Photons are measured by one of three layers of pair spectrometers in the outer region. The total photon detection efficiency is about 6%; the expected photon energy resolution is 1.7 MeV FWHM and the angular resolution is 10 deg FWHM. The time resolution between the photon and electron is 0.8 ns FWHM. About 10{sup 8} events that passed the on-line inters were recorded during the 1993 run. These data should have a branching ratio sensitivity approximately fifteen times better than the present limit. The measured resolutions are approaching the design values.