Kavli Affiliate: T. Higuchi
| First 5 Authors: K. Ravindran, K. Adamczyk, H. Aihara, S. Bacher, S. Bahinipati
| Summary:
In 2024, the Belle II experiment resumed data taking after the Long Shutdown
1, which was required to install a two-layer pixel detector and upgrade
accelerator components. We describe the challenges of this shutdown and the
operational experience thereafter. With new data, the silicon-strip vertex
detector (SVD) confirmed the high hit efficiency, the large signal-to-noise
ratio, and the excellent cluster position resolution. In the coming years, the
SuperKEKB peak luminosity is expected to increase to its target value,
resulting in a larger SVD occupancy caused by beam background. Considerable
efforts have been made to improve SVD reconstruction software by exploiting the
excellent SVD hit-time resolution to determine the collision time and reject
off-time particle hits. A novel procedure to group SVD hits event-by-event,
based on their time, has been developed using the grouping information during
reconstruction, significantly reducing the fake rate while preserving the
tracking efficiency. The front-end chip (APV25) is operated in the multi-peak
mode, which reads six samples. A 3/6-mixed acquisition mode, based on the
timing precision of the trigger, reduces background occupancy, trigger
dead-time, and data size. Studies of the radiation damage show that the SVD
performance will not seriously degrade during the lifetime of the detector,
despite moderate radiation-induced increases in sensor current and strip noise.
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