First results from the MuPix8, a large HV-MAPS prototype

The Mu3e experiment is searching for the charged lepton flavor violating (cLFV) decay $\mu$ $\to$ eee with a planned sensitivity of 1 in 10${}^{15}$ decays for phase 1. To achieve such a sensitivity, a fast, high resolution tracking detector is required which has a material budget of 1 to reduce multiple Coulomb scattering. A suitable technology for these requirements is the High Voltage Monolithic Active Pixel Sensor (HV-MAPS) concept. It combines fast charge collection via drift with a fully monolithic architecture of sensor and readout in one chip which can be thinned to 50 $\mu$m. The MuPix8 is the first large scale HV-MAPS prototype for Mu3e with a size of 1$\times$2 cm${}^2$. Efficiency and time resolution have been measured in testbeam campaigns at DESY. Additionally, measurements with testpulses and radioactive sources are presented.