Position resolution of the time projection chamber at TRIUMF

The spatial resolution of the TRIUMF time projection chamber (TPC) was investigated. The dominant effects on the resolution are diffusion, track-anode crossing angle, E vector x B vector forces in the region of the anode wire and clustering of the primary ionization. A formulation of these effects has been used to determine the mean collision time, the diffusion constant, the Lorentz angle in the anode wire region and the spatial resolution as a function of the crossing angle for a gas mixture of Ar (80%), CH4 (20%) at atmospheric pressure. The minimum resolution, sigma approx.200μm, occurs when the track crossing angle equals the Lorentz angle. As the angle moves away from this value the resolution deteriorates rapidly due to the discrete nature of the ionization process