Kavli Affiliate: T. Higuchi
| First 5 Authors: S. Mondal, K. Adamczyk, L. Aggarwal, H. Aihara, T. Aziz
| Summary:
The silicon vertex detector (SVD) is installed at the heart of the Belle II
experiment, taking data at the high-luminosity $B$-Factory SuperKEKB since
2019. The detector has shown a stable and above-99% hit efficiency, with a
large signal-to-noise in all sensors since the beginning of data taking.
Cluster position and time resolution have been measured with 2020 and 2022 data
and show excellent performance and stability. The effect of radiation damage is
visible, but not affecting the performance. As the luminosity increases, higher
machine backgrounds are expected and the excellent hit-time information in SVD
can be exploited for background rejection. In particular, we have recently
developed a novel procedure to select hits by grouping them event-by-event
based on their time. This new procedure allows a significant reduction of the
fake rate, while preserving the tracking efficiency, and it has therefore
replaced the previous cut-based procedure. We have developed a method that uses
the SVD hits to estimate the track time (previously unavailable) and the
collision time. It has a similar precision to the estimate based on the drift
chamber but its execution time is three orders of magnitude smaller, allowing a
faster online reconstruction that is crucial in a high luminosity regime. The
track time is a powerful information provided to analysis that allows, together
with the above-mention grouping selection, to raise the occupancy limit above
that expected at nominal luminosity, leaving room for a safety factor. Finally,
in June 2022 the data taking of the Belle II experiment was stopped to install
a new two-layer DEPFET detector (PXD) and upgrade components of the
accelerator. The whole silicon tracker (PXD+SVD) has been extracted from Belle
II, the new PXD installed, the detector closed and commissioned. We briefly
describe the SVD results of this upgrade.
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