Abstract
The Belle II experiment is a new generation B-factory experiment at KEK in Japan aiming at the search for New Physics in a huge sample of B-meson decays. The commissioning of the accelerator and the detector for the first physics run has started from March this year. The Belle II High Level Trigger (HLT) is fully working in the beam run. The HLT is now operated with 1600 cores clusterized in 5 units, which is 1/4 of the full configuration. The software trigger is performed using the same offline reconstruction code, and events are classified into a set of physics categories. Only the events in the categories of interest are finally sent out to the storage. Live data quality monitoring is also performed on HLT. For the selected events, the reconstructed tracks are extrapolated to the surface of the pixel detector (PXD) and quickly fed back to the readout electronics for the real time data reduction by sending only the associated hits. The maximum trigger rate in the first physics run was 3.5kHz, and the Belle II data acquisition system was stably operated. There were several problems in the HLT operation, but they have successfully been fixed during the data taking period. The HLT reduction factor is measured to be 8 which is still higher than the design because of the high background environment.
Highlights
The Belle II experiment[1], which is a new generation B-factory experiment, has just started the physics data taking
The physics run with all detectors with the vertex detectors installed started from March 2019 and the data taking with a full data acquisition system (DAQ) configuration is being performed (Phase 3)
In the stable physics run, the efficiency is more than 90%
Summary
The Belle II experiment[1], which is a new generation B-factory experiment, has just started the physics data taking. The data acquisition system (DAQ) for the experiment is required to manage a Level 1 trigger rate up to 30 kHz with an event size of more than 1 MB, and the high-speed readout and data reduction are the key of the DAQ. The commissioning of the SuperKEKB accelerator started from February, 2016 including the accelerator tuning and vacuum scrubbing (Phase 1). The first electron-positron collision was observed in April 2018 and the pilot run was performed only with the outer detectors (Phase 2). The physics run with all detectors with the vertex detectors installed started from March 2019 and the data taking with a full DAQ configuration is being performed (Phase 3)
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