Track based alignment for the Mu3e detector

The Mu3e experiment searches for the lepton flavor violating decay μ → e⁺e⁺e^- with a sensitivity goal for the branching fraction of better than 10^-16. This process is heavily supressed in the standard model of particle physics (BR< 10^-50) which makes an observation of this decay a clear indication of new physics. For track reconstruction, four barrel shaped layers consisting of about 3000 high-voltage monolithic active pixel sensors (HV-MAPS) are used. The position, orientation and possible deformations of these sensors must be known to greater precision than the assembly tolerances. A track based alignment via the General Broken Lines fit and the Millepede-II algorithm will be used to achieve this precision in the final detector. The talk will discuss preparations for aligning the detector using a detailed simulation. A set of alignment parameters that not only describe the position and rotation but also deformations of individual pixel sensors will be introduced. An alignment for these kind of parameters is - due to the very thin (50 μm) pixel sensors - essential for the Mu3e detector.