Studies of wire gain and track distortion near the sector edges of the ALEPH time projection chamber

Abstract The materials used to hold the wires at the sector edges in a large Time Projection Chamber (TPC) inrtoduce distortions of the electric drift field near those edges. These distortions degrade tracking information and sometimes cause large changes in wire gain near the edge. We have studied these two problems for the ALEPH TPC and have found that both can be greatly reduced by the addition of two field correction strips held at appropriate voltages.