The Mu3e scintillating fiber timing detector

Abstract

A new experiment, Mu3e, to search for charged Lepton Flavor Violation in the rare neutrinoless μ+→e+e+e− decay is in preparation at the Paul Scherrer Institute using the most intense continuous surface muon beam in the world. The Mu3e detector is based on thin monolithic active silicon pixel sensors (HV-MAPS) for very precise tracking in conjunction with scintillating fibers and scintillating tiles coupled to silicon photomultipliers (SiPMs) for accurate timing measurements and is designed to operate at very high intensities.In order to reach a sensitivity of 10−16, all backgrounds must be rejected below this level. To suppress all forms of combinatorial background, a very thin (thickness ∼0.2% of a radiation length X0) Scintillating Fiber detector with few 100 ps time resolution, efficiency in excess of 96%, and spatial resolution of ∼100μm has been developed. In this paper we report on the development and performance of the fiber detector, from the scintillating fiber ribbons through the SiPM array photo-sensors up to the front end electronics.