Development and Performance of the Belle II DAQ Upgrade

Belle II is a new-generation B-factory experiment operating at the luminosity frontier, SuperKEKB collider, and started data-taking in April 2018. Belle~II uses a synchronous data acquisition (DAQ) system based on a pipelined trigger flow control. It is designed to handle 30 kHz trigger rate, under the assumption of a raw event size 1 MB. Because a larger event size and rate are foreseen depending on the future background conditions, and the difficult maintainability of the current readout system during the Belle II entire operation period is expected, we decided to upgrade the Belle II DAQ readout system with state-of-art technology. A PCI Express based new-generation of readout board (PCIe40), which was originally developed for the upgrade of LHCb and ALICE experiments, has been used for the upgrade of Belle II DAQ system. PCIe40 is able to connect to a maximum of 48 frontend electronics through multi-gigabit serial links. PCI Express hard IP-based direct memory access architecture, the newly designed timing and trigger distribution system and slow control system make the Belle II readout setup a compact system. Three out of seven sub-detectors of Belle II experiment have been operated with the upgraded DAQ system during physics data-taking, development and performance for remaining sub-detectors have been accomplished and checked with cosmic data-taking and stress DAQ test.