Mu3e has installed the vertex detector for the 2026 beamtime, marking an important milestone in the detector assembly. The two-layer detector built from High-Voltage Monolithic Active Pixel Sensors (HV-MAPS) sits at the core of the experiment and measures tracks of decay particles very close to muon stopping target, allowing for a precise determination of the decay vertex. The ultralight detector is extremely fragile and the installtion procedure requires great care in all steps. The detector is now in place and we can proceed with making electrical connections and installing further detectors - the scintillating fibres are next in line.
