Mechanics and cooling of the Mu3e detector

The Mu3e experiment will search for the charged lepton flavour violating decay μ⁺ → e⁺e^-e⁺, which is suppressed to unobservable levels in the Standard Model. A signal would be a clear sign of new physics. The aim is to reach a sensitivity for the branching ratio of 10^-16, which requires high momentum resolution. Since the muons will decay at rest on target, the energy of the decay electrons will be E≤53 MeV. In this energy regime the momentum resolution is limited by multiple scattering in the detector material. Therefore, the Mu3e detector, including support structure and services, has to consist of as little material as possible in the active region. The main component of the detector is a pixel tracker consisting of four barrels of high voltage monolithic active pixel sensors (HV-MAPS) that can be thinned to 50 μm. A power consumption of 400 mW/cm² is expected. To keep the material budget low, it is planned to cool with gaseous helium. In this talk results of computational fluid dynamics simulations of the Mu3e cooling system and experimental tests concerning the detector's stability against flow-induced vibrations are presented.