Data Acquisition

In order to satisfy the data acquisition requirements so that it works at 500 Hz with a deadtime fraction of less than 10%, the distributed- parallel system has been devised. The global scheme of the system is shown in Fig. . The entire system is segmented into 7 subsystems running in parallel, each handling the data from a sub-detector. Data from each subsystem are combined into a single event record by an event builder, which converts ``detector-by-detector'' parallel data streams to an ``event-by-event'' data river. The event builder output is transferred to an online computer farm, where another level of event filtering is done after fast event reconstruction. The data are then sent to a mass storage system located at the computer center via optical fibres. A typical data size of a hadronic event by $B\bar{B}$ or production is measured to be about 30 kB, which corresponds to the maximum data transfer rate of 15 MB/s.

Figure: Belle DAQ system overview.