Level 1 trigger system for the Belle II experiment

The Super KEKB factory project at KEK in Japan with the ultimate goal of integrated luminosity of 50 ab^-1 has been prepared to study the Beyond Standard Model physics from B meson and tau/charm weak decays. A online trigger system is indispensable to suppress a mount of beam background events from high beam currents of electron and positron and to enhance physics oriented events. Two kind of Level-1 online trigger components are mainly taken into account, a track trigger and a energy trigger. The track trigger is composed of 2D and 3D tracking algorithms, and the energy trigger has total energy and isolated cluster trigger algorithms. In addition, precise trigger timing and muon tagging are extracted from Time of Projection detector and KLM detector, respectively.