Search for lepton flavour violating muon decay mediated by a new light particle in the MEG experiment

We present the first direct search for lepton flavour violating muon decay mediated by a new light particle X, \mu^+ \to \mathrm{e}^+\mathrm{X}, \mathrm{X} \to \gamma\gamma. This search uses a dataset resulting from 7.5\times 10^{14} stopped muons collected by the MEG experiment at the Paul Scherrer Institut in the period 2009--2013.... Show more