Study of a dEdx measurement and the gas-gain saturation by a prototype drift chamber for the BELLE-CDC

We studied the performance of a dEdx measurement using an actual real-size prototype of the Central Drift Chamber for the KEK B-Factory. The observed dependences on the track incident angles showed a gas-gain saturation effect due to the space-charge. This gas-gain saturation caused the chamber response to dEdx of the incident particles to be weaker. We measured gas-gain saturation as a function of the line-charge density on a sense wire made by an incident charged particle, and observed that the line-charge density dominantly determined the gas-gain saturation.