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Boudagga, R. et al, Lacasta, C., Marinas, C., Mazorra de Cos, J., Molina-Bueno, L., & Vobbilisetti, V. (2025). Upgrade of the Belle II vertex detector with depleted monolithic CMOS active sensors. Nucl. Instrum. Methods Phys. Res. A, 1080, 170677–4pp.
Abstract: The Belle II experiment at the SuperKEKB collider in Japan, which currently holds the world luminosity record for electron-positron collisions, plans to upgrade its vertex detector (VXD) to operate at a target luminosity of 6 x 1035 cm-2s-1. A new pixelated vertex detector (VTX) is under development, utilizing a monolithic CMOS pixel sensor named OBELIX (Optimized BELle II pIXel). The VTX design incorporates 5-6 layers with a total material budget below 2.5% X0. All layers will employ the OBELIX, adapted from the TJ-Monopix2 sensor initially designed for the ATLAS Inner Tracker (ITk) upgrade. The OBELIX sensor, designed using a 180 nm CMOS process, features an enhanced pixel matrix and additional functionalities compared to its predecessor. Laboratory tests and test beam characterization results on irradiated and unirradiated TJ-Monopix2 sensors have yielded promising results, confirming the key performance parameters for the OBELIX design. This paper reviews the overall design of the VTX and the OBELIX sensor and presents the latest results of the in-beam characterization of the TJ-Monopix2.
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Torres-Espallardo, I., Diblen, F., Rohling, H., Solevi, P., Gillam, J., Watts, D., et al. (2015). Evaluation of resistive-plate-chamber-based TOF-PET applied to in-beam particle therapy monitoring. Phys. Med. Biol., 60(9), N187–N208.
Abstract: Particle therapy is a highly conformal radiotherapy technique which reduces the dose deposited to the surrounding normal tissues. In order to fully exploit its advantages, treatment monitoring is necessary to minimize uncertainties related to the dose delivery. Up to now, the only clinically feasible technique for the monitoring of therapeutic irradiation with particle beams is Positron Emission Tomography (PET). In this work we have compared a Resistive Plate Chamber (RPC)-based PET scanner with a scintillation-crystal-based PET scanner for this application. In general, the main advantages of the RPC-PET system are its excellent timing resolution, low cost, and the possibility of building large area systems. We simulated a partial-ring scannerbeam monitoring, which has an intrinsically low positron yield compared to diagnostic PET. In addition, for in-beam PET there is a further data loss due to the partial ring configuration. In order to improve the performance of the RPC-based scanner, an improved version of the RPC detector (modifying the thickness of the gas and glass layers), providing a larger sensitivity, has been simulated and compared with an axially extended version of the crystal-based device. The improved version of the RPC shows better performance than the prototype, but the extended version of the crystal-based PET outperforms all other options. based on an RPC prototype under construction within the Fondazione per Adroterapia Oncologica (TERA). For comparison with the crystal-based PET scanner we have chosen the geometry of a commercially available PET scanner, the Philips Gemini TF. The coincidence time resolution used in the simulations takes into account the current achievable values as well as expected improvements of both technologies. Several scenarios (including patient data) have been simulated to evaluate the performance of different scanners. Initial results have shown that the low sensitivity of the RPC hampers its application to hadron
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