Comparative studies of FCC vertex detector layouts.

The performance of the vertex detector is critical for achieving the precision tracking and flavor-tagging goals of the Future Circular Collider. This study presents detailed geometry investigations of the FCC vertex detector using the IDEA baseline design as a reference. We explore the impact of several alternative configurations on key performance metrics, including impact parameter resolution and momentum resolution. In particular, we examine scenarios where the innermost layer is positioned directly on top of the beam pipe, a compact short-barrel geometry, and an innovative layout with the first layer placed inside the beam pipe. Additionally, the influence of different solenoidal magnetic field strength, specifically 2 T and 3 T, on vertexing and tracking performance is evaluated. Comparative results provide guidance for optimizing the vertex detector design for future FCC physics goals.