The Silicon Vertex Detector of the Belle II Experiment

TL;DR

The Belle II Silicon Vertex Detector has operated reliably since 2019, providing high-quality data with high efficiency and stability, and strategies are being developed to maintain performance at higher luminosities.

Contribution

This paper details the operational performance, stability, and radiation resilience of the Belle II SVD, and introduces strategies to sustain tracking performance at increased luminosity levels.

Findings

High signal-to-noise ratio and >99% hit efficiency achieved.

Low occupancy (~0.5%) with no impact on data reconstruction.

No detrimental effects observed from radiation damage or intense beam bursts.

Abstract

Since the start of data taking in spring 2019 at the SuperKEKB collider (KEK, Japan) the Belle II Silicon Vertex Detector (SVD) has been operating reliably and with high efficiency, while providing high quality data: high signal-to-noise ratio, greater than 99% hit efficiency, and precise spatial resolution. These attributes, combined with stability over time, result in good tracking efficiency. Currently the occupancy, dominated by beam-background hits, is quite low (about 0.5% in the innermost layer), causing no problems to the SVD data reconstruction. In view of the operation at higher luminosity foreseen in the next years, specific strategies aiming to preserve the tracking performance have been developed and tested on data. The time stability of the trigger allows reducing sampling of the strip-amplifier waveform. The good hit-time resolution can be exploited to further improve the robustness against the higher level of beam background. First effects of radiation damage on strip noise, sensor currents and depletion voltage have been measured: they do not have any detrimental effect on the performance of the detector. Furthermore, no damage to the SVD is observed after sudden and intense bursts of radiation due to beam losses.