Speaker
Description
The Belle II experiment at the SuperKEKB asymmetric e+e⁻ collider recorded data from 2019 to 2022, before entering its first long shutdown. During this period, 428 fb⁻¹ of data were collected at the Y(4S) resonance, where the cross section for B-meson pair production is highest.
During the shutdown, the PiXel detector (PXD), which forms the inner two layers of the VerteX detector (VXD), was replaced by a new detector with a fully populated second layer. This PXD2 retains the DEPFET technology of its predecessor and thus comprises all-silicon modules integrating both the support structure and sensors with pixel sizes ranging from 50×55 μm² to 50×85 μm², thinned down to 75 μm in the sensitive region, resulting in a material budget of 0.21% X₀ per layer. Readout is handled by 14 ASICs of three types, which are bump-bonded to the sensors. The cooling system consists of a two-phase CO₂ system for the readout ASICs and N₂ gas flow for the low power sensor matrix.
Installation of PXD2 was completed in summer 2023, followed by full integration testing. Beam operation commenced in February 2024. Since May, PXD2 has been temporarily shut down for safety reasons after being partially damaged by two uncontrolled beam losses. PXD2 is expected to resume operation in 2025 after modifications on the accelerator side.
This presentation will cover the installation, commissioning, early operation and performance of PXD2 compared to PXD1, as well as the impact of beam-induced damage.
| Primary experiment | Belle II |
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