Readout via Flexprints for the Mu3e Experiment

The Mu3e experiment at PSI aims to search for the charged lepton flavor violating decay µ + → e +e −e + with a sensitivity to a branching ratio of 10−16. To achieve this, a high intensity muon beam with a rate of 108 - 109 muons per second is stopped on a target. The decay electrons are detected with a silicon pixel tracking detector using High Voltage Monolithic Active Pixel Sensors (HV-MAPS) and timing detectors consisting of scintillating fibres and tiles. Instead of a triggered readout, the experiment uses online event filtering. This requires the readout of all hits detected in the pixel sensors. Hence, data from the sensors is transferred using fast serial LVDS links with data rates of 1.25 Gb/s over flex-print cables made of polyimide and aluminium foil. The flex-prints also provide power and control signals. In total, about 1000 sensors have to be powered and read out with one to three fast serial data links each. Studies of the serial data transmitted from the current pixel sensor prototype MUPIX7 at 1.25 Gb/s have been performed. Flex-print cables produced in-house have been tested regarding impedance, quality of service, and bandwidth. An outlook on the flex-print design to connect the next generation of MUPIX sensors and build first detector modules is given.