STUDY OF A DE DX MEASUREMENT AND THE GAS-GAIN SATURATION BY A PROTOTYPE DRIFT CHAMBER FOR THE BELLE-CDC/

We studied the performance of a dE/dx measurement using an actual real -size prototype of the Central Drift Chamber for the KEK B-Factory. Th e observed dependences on the track incident angles showed a gas-gain saturation effect due to the space-charge. This gas-gain saturation ca used the chamber response to dE/dx of the incident particles to be wea ker, We measured gas-gain saturation as a function of the line-charge density on a sense wire made by an incident charged particle, and obse rved that the line-charge density dominantly determined the gas-gain s aturation.