The Mu3e experiment will search for the rare neutrinoless lepton flavor
violating mu+ -> e+e+e- decay and it aims at reaching an ultimate sensitivity
of 10^-16 on this branching ratio. The experiment will be performed at PSI
using the most intense continuous surface muon beam in the world (presently
~1x10^8 mu/s). In order to reach this sensitivity all backgrounds must be
rejected below this level. The Mu3e detector is based on thin monolithic
active silicon pixel sensors (HV-MAPS) for very precise tracking in conjunction
with scintillating fibers and tiles coupled to Si-PMs for accurate timing
measurements and is designed to operate at very high intensities.
To suppress all forms of combinatorial background a very thin (thickness < 0.2%
of radiation length) Scintillating Fiber (SciFi) detector with few 100 ps time
resolution, efficiency in excess of 96%, and spatial resolution of ~100 um has
been developed. Moreover the SciFi detector will help to determine the charge
of the recurling tracks in the central region of the apparatus. The SciFi arrays
are coupled at both ends to Si-PM arrays and are read out with a dedicated mixed
mode ASIC, the MuTRiG.
We will report in detail the development of the SciFi detector, from the
scintillating fiber through the Si-PM array photo-sensors up to the front end
electronics and the data acquisition. We will discuss the performance of the
SciFi detector prototypes as observed in our studies.