2023/07/27 by Rudzki, Thomas Theodor, Augustin, Heiko, Immig, David Maximilian +2
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Instrumentation and Detectors (physics.ins-det)
paper · doi:10.48550/arxiv.2307.14803
The Mu3e experiment searches for the lepton flavour violating decay μ+ → e+ e- e+ with an ultimate aimed sensitivity of 1 event in 1016 decays. To achieve this goal, the experiment must minimize the material budget per tracking layer to X/X0≈ 0.1 % and use gaseous helium as coolant. The pixel detector uses High-Voltage Monolithic Active Pixel Sensors (HV-MAPS) which are thinned down to 50 μm. Both helium cooling and HV-MAPS are a novelty for particle detectors. Here, the work on successfully cooling a pixel tracker using gaseous helium is presented. The thermal studies focus on the two inner tracking layers, the Mu3e vertex detector, and the first operation of a functional thin pixel detector cooled with gaseous helium. The approach, which circulates gaseous helium under ambient pressure conditions with a gas temperature around 0 °C using a miniature turbo compressor with a mass flow of 2 g/s allows the vertex detector to operate below 70 °C at heat densities of up to 350 mW/cm2. Finally, performance data of the final HV-MAPS used by Mu3e, the MuPix11, is presented. These results demonstrate the feasibility of using HV-MAPS combined with gaseous helium as a coolant for an ultra-thin pixel detector exploring new frontiers in lepton flavor.