The Belle II Central Drift Chamber(CDC) detects charged particle and measure its momentum under magnetic field. The CDC also provide a pulse height information of the charged particle to identify particle species.

- structure

The CDC consists of 30 um diameter tungsten wires and 120 um diameter aluminum wires. Total number of wires is over 50,000. Those are strung between forward and backward endplates, which are supported by cylindrical inner and outer walls.
The wires are strung coaxially and form rectangular “cell”s which size is about 1.8 cm x 1.8 cm.

-principles

Since CDC cells are worked as independent proportional chambers, the signal pulse height is proportional to energy loss of the charged particle. And also the time between particle passing in the cell and signal creation is measured, which is call as “drift time”. The drift time reflects the distance between particle passing position in the cell and the sense wire position of the cell. The track of charged particle is reconstructed by connecting the passing position.