The MEG positron spectrometer

An innovative positron spectrometer for the MEG experiment has been developed at the Paul Scherrer Institute (PSI) in Switzerland. This experiment will search for a lepton flavor violating decay μ + → e + γ with a sensitivity of 10 - 13 in branching ratio in order to explore the parameter region predicted by the supersymmetric extensions of the standard model. G positron spectrometer consists of a superconducting solenoidal magnet specially designed to form a highly graded field, an ultimate low-mass drift chamber system, and a precise time measuring counter system. In December 2006, the first commissioning run was performed. The spectrometer design and its commissioning are described here.