Minimizing dead time of the Belle II data acquisition system with pipelined trigger flow control

The Belle II detector at the SuperKEKB collider is a general purpose spectrometer to study B meson, charm hadron and τ lepton decays with an unprecedented high luminosity of 8 × 10³⁵ cm^-2s^-1. At Belle II, detector signals are digitized inside or near the detector and collected via high-speed optical serial links. The maximum design trigger rate is 30 kHz, for which we have to record data from 7 subdetectors with a minimum dead-time fraction. Due to complex constraints in the frontend electronics of the Belle II subdetectors, a straightforward dead-time control method does not meet our requirement. We report a pipelined trigger flow control scheme which will keep the dead-time fraction due to the trigger distribution and readout system below 1%.