M. Heck

A neural network z-vertex trigger for Belle II

We present the concept of a track trigger for the Belle II experiment, based on a neural network approach, that is able to reconstruct the z (longitudinal) position of the event vertex within the latency of the first level trigger. The trigger will thus be able to suppress a large fraction of the dominating background from events outside of the interaction region. The trigger uses the drift time information of the hits from the Central Drift Chamber (CDC) of Belle II within narrow cones in polar and azimuthal angle as well as in transverse momentum (sectors), and estimates the z-vertex without explicit track reconstruction. The preprocessing for the track trigger is based on the track information provided by the standard CDC trigger. It takes input from the 2D (

A z-vertex trigger for Belle II

r - \varphi

An automated framework for hierarchical reconstruction of B mesons at the Belle II experiment

) track finder, adds information from the stereo wires of the CDC, and finds the appropriate sectors in the CDC for each track in a given event. Within each sector, the z-vertex of the associated track is estimated by a specialized neural network, with a continuous output corresponding to the scaled z-vertex. The input values for the neural network are calculated from the wire hits of the CDC.

Search for B -> h(*) nu nubar with the full Belle Y(4S) data sample

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.

The Full Event Interpretation -- An exclusive tagging algorithm for the Belle II experiment.

We present a software framework for Belle II that reconstructs B mesons in many decay modes with minimal user intervention. It does so by reconstructing particles in user-supplied decay channels, and then in turn using these reconstructed particles in higher-level decays. This hierarchical reconstruction allows one to cover a relatively high fraction of all B decays by specifying a limited number of particle decays. Multivariate classification methods are used to achieve a high signal-to-background ratio in each individual channel. The entire reconstruction, including the application of pre-cuts and classifier trainings, is automated to a high degree and will allow users to retrain to account for analysis-specific signal-side selections.