Single-electron longitudinal diffusion in helium-isobutane gas mixtures

The single-electron longitudinal diffusion has been measured in several helium-isobutane gas mixtures and compared with computations based on electron transport theories. A discussion on the transverse momentum resolution of a 200 Mev/c charged π as a function of its track length in a drift chamber is presented and conclusions are drawn on the choice of the optimal gas mixture.