A. Kumar, et al.

16 October 2024

Abstract: The Belle II experiment at the SuperKEKB accelerator in Japan is dedicated to exploring physics beyond the Standard Model by performing high-precision measurements of heavy-flavor processes. The SuperKEKB will undergo a major upgrade during a second long shutdown to achieve the target luminosity of 6$\times$10$^{35}$ cm$^{-2}$s$^{-1}$. The vertex detector is a critical component of Belle II, responsible for precise tracking and vertexing near to the interaction point. The current vertex detector will be upgraded to a fully pixelated vertex detector (VTX) based on Monolithic Active Pixel Sensors (MAPS) technology to enhance performance and address challenges from increasing luminosity. The VTX will consist of five layers of depleted MAPS sensor, called OBELIX, with radii from 14~mm to 140~mm and a material budget ranging from 0.2-0.8$\%$~X/X$_{0}$ per layer. The OBELIX sensor is derived from the TJ-Monopix2 sensor, originally developed under TowerJazz 180~nm for the ATLAS experiment. This paper discusses the design, implementation, and expected performance of the VTX, highlighting the technical advances brought by MAPS technology, which offer significant advantages in terms of material budget, radiation hardness, and spatial resolution. The motivation for this upgrade, the design considerations, and the expected performance improvements are analyzed.

Note: The first version of ICHEP 2024 proceedings.