The silicon vertex detector of the Belle II experiment

초록

The Belle II experiment is taking data at the asymmetric SuperKEKB collider (KEK, Japan), which operates at the gamma(4S) resonance. The vertex detector is composed of an inner two-layer pixel detector (PXD) and the silicon vertex detector (SVD), made of four layers of double-sided silicon strip detectors. A deep knowledge of the system has been gained since the start of operations in 2019 by assessing the high-quality and stable reconstruction performance of the detector. The very high hit efficiency and large signal-to-noise ratio are monitored via online data-quality plots. The good cluster-position resolution is estimated using the unbiased residual with respect to the track, and it is in reasonable agreement with the expectations. The SVD dose is estimated by the correlation of the SVD occupancy with the dose measured by the diamond sensors of the radiation-monitoring and beam-abort system. First radiation damage effects are measured on the sensor current and strip noise are shown not to affect the performance. Six samples of the shaped particle signal are recorded utilizing the multi-peak mode of the APV25 front-end chip and used to determine the hit timing with a precision of 2 to 3 ns. Recently a method to compute the time of collision from SVD hit time information has been implemented and verified with simulations and on data.

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