The Belle II detector is a general purpose spectrometer for the next-generation B-factory experiment at KEK. The Belle II efficiently collects data of e+e- collisions made by the SuperKEKB accelerator. The Belle II consists of several sub-detector components:

• two layers of pixelated silicon sensors (PXD) and four layers of double-sided silicon strip sensors (SVD) that measure decay vertex positions of B mesons and other particles,
• a central drift chamber (CDC) that measures trajectories, momenta and dE/dx information of charged particles,
• a barrel-shaped array of Time-Of-Propagation (TOP) counters that reconstruct, in spacial and time coordinates, the ring-image of Cherenkov light cones emitted from charged particles passing through quartz radiator bars, another ring-imaging Cherenkov counters with aerogel radiator in the forward end-cap (A-RICH),
• an electromagnetic calorimeter (ECL) comprised of scintillator crystals located inside a superconducting solenoid coil that provides a 1.5 Tesla magnetic field, and
• an iron flux-return located outside of the coil which is instrumented to detect K0L mesons and to identify muons (KLM).

There are other tasks essential for the detector:

• a fast and reliable trigger (TRG) and data acquisition system (DAQ) records collision events of interest,
• stable operation of superconducting solenoid magnet,
• a globally-distributed computing and data-storage system and organized effort on various levels of software that work on the computer (Soft/Comp),
• an arrangement of components around the Interaction Region (IR), such as beam pipes and final focusing magnets, which directly impacts the amoung of beam backgrounds, and
• an integrated effort on the mechanical structure design (STR).

You may find more details in the internal page for detectors.