New result from the MEG Experiment at PSI and the MEG upgrade

The analysis of a combined data set, totaling 3.6×1014 stopped muons on target, in the search for the lepton flavor violating decay μ+→e+γ is presented. The data collected by the MEG experiment at the Paul Scherrer Institut show no excess of events compared to background expectations and thus yield a new upper limit on the branching ratio of this decay of 5.7×10−13 @ 90% CL [J. Adam, et al., New constraint on the existence of the μ+→e+γ decay, Phys. Rev. Lett. 110 (2013) 201801. arXiv:1303.0754]. At this point of data taking the background became dominant and an improvement of the sub detectors resolution was needed in order to obtain in few years a significant improvement in the branching ratio upper limit. An upgrade of the MEG experiment was proposed [A. Baldini, F. Cei, C. Cerri, S. Dussoni, L. Galli, et al., MEG Upgrade Proposal, arXiv:1301.7225] and approved in January 2013.