EXPERIMENTAL-STUDY OF MUONIUM-ANTIMUONIUM CONVERSION AT THE PHASOTRONOF THE JOINT-INSTITUTE-FOR-NUCLEAR-RESEARCH

An experimental search has been made for muonium-antimuonium conversio n (M-->MBAR) in an intense beam of surface muons produced at the phaso tron of the Joint Institute for Nuclear Research. A wide-angle magneti c lens was used. This experiment was carried out as a collaboration be tween St. Petersburg Institute of Nuclear Physics and the JINR. A new method was used. It is based on the detection of high-energy electrons from the decay of the muon of the antimuonium by a wide-aperture magn etic spectrometer. This method provides a high luminosity for the dete ction of the conversion process, along with a low background. No event s associated with the M-->MBAR conversion were detected. A limit W(MMB AR) < 3.9 x 10(-7) (at a 90% confidence level) was established on the probability for the conversion process, with respect to ordinary muon decay. This limit is better than the limit which previously existed by a factor of 1.7 The new value for the muonium-antimuonium conversion constant is G(MMBAR) < 0.13 . G(F) (90% CL).