A z-vertex trigger for Belle II

The Belle II experiment [1], the successor of the Belle experiment [2], will go into operation at the upgraded KEKB collider (“SuperKEKB”) in 2016 [3], [4]. SuperKEKB is designed to deliver an instantaneous luminosity ℒ = 8×1035 cm-2 s-1, a factor of 40 larger than the previous KEKB world record. The Belle II experiment will therefore have to cope with a much larger machine background than its predecessor Belle. Especially the Touscheck scattering [5], [6] is expected to increase significantly, leading to charged track events with displaced z-vertex positions. This makes a powerful z-vertex trigger for Belle II crucial.