A limit for the μ→eγμ→eγ decay from the MEG experiment

A search for the decay μ+→e+γμ+→e+γ, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR(μ+→e+γ)⩽2.8×10−11BR(μ+→e+γ)⩽2.8×10−11 (90% C.L.). This corresponds to the measurement of positrons and photons from ∼1014∼1014 stopped μ+μ+-decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.