Mechanical design of an ultra-light vertex detector prototype for CEPC

Background The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed to study the Higgs boson in great detail. It requires state-of-the-art detectors, including extremely precise vertexing and tracking devices, such as a silicon vertex detector. Purpose Silicon vertex detector with the precision required by the CEPC has never been built before and needs extensive research and development. This paper describes the mechanical design of a vertex detector prototype being built to explore the required technologies and the major challenges. Methods The exceptional high spatial resolution of the CEPC vertex detector is achievable only with a detector of extremely low mass to limit particle scattering. This paper proposes a mechanical design for the vertex detector prototype, highlighting the choice of low-mass materials, the analysis of support structures, the solution of detector cooling issues, and the drafts of procedures for detector assembly. Results The ultra-light support of the ladder (a structural unit of the CEPC vertex detector prototype), which is mainly made of carbon fiber reinforced polymer composite, has been designed. The fabrication process has also been verified. Global supporting and cooling method of the vertex detector prototype has been designed and chosen with results from finite element analysis and computational fluid dynamics simulations. Complete assembly and installation schemes for the prototype have been developed, and the respective tooling has also been designed. The performance of the vertex detector prototype, using this low-mass mechanical structure, was demonstrated with fast simulation to closely meet the CEPC physics requirement.