Development of the scintillating fiber timing detector for the MU3E experiment

We present the development and discuss the performance of a compact scintillating fiber detector for the Mu3e experiment for accurate time measurements at very high particle rates. Mu3e is a new experiment under preparation at the Paul Scherrer Institut (PSI) to search for charged Lepton Flavor Violation in the neutrinoless muon decay u(+)-> e(+)e(-)e(+) with a projected sensitivity of 10(-16) using the most intense continuous surface muon beam in the world. A very thin scintillating fiber detector (thickness <0.2% of a radiation length x(0)) with a time resolution of about 250 ps, efficiency around 97%, and spatial resolution of similar to 100(um) has been developed. The SciFi detector is read out with multi-channel silicon photomultiplier arrays at both ends to achieve the best timing performance. Different scintillating fiber types have been evaluated and various assembly procedures have been tested to achieve the best performance.