On Oct. 13th 2016, the Central Drift Chamber (CDC) for the Belle II detector was successfully installed.
The CDC is a crucial sub-detector, as it provides the momentum of electrically-charged particles by reconstructing their curved trajectories while moving in a magnetic field. The information provided by the CDC is also a key ingredient of the Belle II trigger system. Additionally, the CDC contributes to particle identification by measuring the energy loss of charged particles as they pass through the gas that fills the CDC.
The CDC is a large cylindrical-shaped gas detector, with inner and outer radii of about 16 cm and 113 cm, respectively. This cylindrical volume is filled with a helium-based gas mixture. When a charged particle passes through the gas-filled chamber, it ionizes the gas molecules by knocking out electrons. An electric field is created by applying high voltages to sense wires strung across the chamber. This electric field causes the electrons which have been knocked loose to accelerate towards additional sense wires, which have a small positive voltage. The movement of these charge carriers towards the sense wires induces an electrical signal that can be measured.