Speaker
Description
The Belle II experiment at SuperKEKB operates at a record luminosity of $5.1 \times 10^{34}~\mathrm{cm}^{-2}~\mathrm{s}^{-1}$, with plans to reach $6 \times 10^{35}~\mathrm{cm}^{-2}~\mathrm{s}^{-1}$. To handle higher backgrounds and improve tracking precision, an upgraded vertex detector (VTX) is needed. The new VTX will feature 5-6 layers equipped with OBELIX, a depleted monolithic active pixel sensor designed for high space-time granularity, low material budget ($<3\%~X_0$), and robustness to machine-induced backgrounds.
Based on Tower 180 nm technology and derived from the TJ-Monopix2 sensor (originally for ATLAS), it offers a $33~\mu\mathrm{m}$ pitch, precise time stamping, and, thanks to its new digital periphery, supports Belle II's 30 kHz trigger rate, handling hit rates up to $120~\mathrm{MHz}/\mathrm{cm}^2$.
Extensive laboratory and beam testing of TJ-Monopix2, including irradiated samples (NIEL up to $5 \times 10^{14}~\mathrm{n}_{\mathrm{eq}}/\mathrm{cm}^2$ and TID up to 100~Mrad), highlight its strong post-irradiation performance under various conditions.
These results not only optimise OBELIX's design for Belle II's challenging background conditions, but also demonstrate its potential for future high-energy physics experiments in extreme environments, such as FCC-ee.
