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Mu3e is a novel experiment searching for charged lepton flavor violation in the rare decay µ + → e + e − e + . Decay vertex position, decay time and particle momenta have to be precisely measured in order to reject both accidental and physics background. A silicon pixel tracker based on 50 µm thin high voltage monolithic active pixel sensors (HV-MAPS) in a 1 T solenoidal magnetic field provides precise vertex and momentum information. The MuPix chip combines pixel sensor cells with integrated analog electronics and a periphery with a complete digital readout. The MuPix7 is the first HV-MAPS prototype implementing all functionalities of the final sensor including a readout state machine and high speed serialization with 1.25 Gbit/s data output, allowing for a streaming readout in parallel to the data taking. The observed efficiency of the MuPix7 chip including the full readout system is ≥ 99% in a high rate test beam.

The accurate determination of atomic final states following nuclear β decay plays an important role in several experiments. In particular, the charge state distributions of ions following nuclear β decay are important for determinations of the β − ν angular correlation with improved precision. Beyond the hydrogenic cases, the decay of neutral 6 He presents the simplest case. Our measurement aims at providing benchmarks to test theoretical calculations. The kinematics of Li n+ ions produced following the β decay of 6 He within an electric field were measured using 6 He atoms in the metastable (1s2s, 3 S1) and in the (1s2p, 3 P2) states confined by a magneto-optical trap. The electron shake-off probabilities were deduced including their dependence on ion energy. We find significant discrepancies on the fractions of Li ions in the different charge states with respect to a recent calculation.

The MuPix7 chip is a monolithic HV-CMOS pixel chip, thinned down to 50 µm. It provides continuous self-triggered, non-shuttered readout at rates up to 30 Mhits/chip of 3 × 3 mm 2 active area and a pixel size of 103 × 80 µm 2 . The hit efficiency depends on the chosen working point. Settings with a power consumption of 300 mW/ cm 2 allow for a hit efficiency > 99.5%. A time resolution of 14.2 ns (Gaussian sigma) is achieved. Latest results from 2016 test beam campaigns are shown.

The MuPix Telescope is a particle tracking telescope, optimized for tracking low momentum particles and high rates. It is based on the novel High-Voltage Monolithic Active Pixel Sensors (HV-MAPS), designed for the Mu3e tracking detector. The telescope represents a first application of the HV-MAPS technology and also serves as test bed of the Mu3e readout chain. The telescope consists of up to eight layers of the newest prototypes, the MuPix7 sensors, which send data self-triggered via fast serial links to FPGAs, where the data is time-ordered and sent to the PC. A particle hit rate of 1 MHz per layer could be processed. Online tracking is performed with a subset of the incoming data. The general concept of the telescope, chip architecture, readout concept and online reconstruction are described. The performance of the sensor and of the telescope during test beam measurements are presented.