Pressure Dependence of the Relativistic Rise in Neon and Highest Attainable Ionization Sampling Resolution in Neon, Argon, Ethylene and Propane

A full-scale detector segment with 128 samples of 2 cm and a 50 cm drift space was used to measure precisely the relativistic rise of ionization from 5 to 70 GeV/c in Ne at 1, 2 and 4 atm. The pressure dependence of dE/dx resolution and of particle separation efficiency was determined at 15 GeV/c in several Ne/CnHm mixtures, in Ar/CH4, pure C2H4 and pure C3H8. The results are used for optimization of parameters of a compact colliding beam detector suitable for particle identification up to the 30-50 GeV/c momentum range. The π/K/p separation is found to be better in Ne, but extends to higher momenta in Ar. Ar is more efficient for e/π separation. The gain in resolution at higher pressures is to certain extent compensated by reduction of the relativistic rise slope, so that the separation efficiency is reduced when the detector dimensions are scaled down with pressure. At 4-5 atm. we obtained slightly better resolution than the 6.0% FWHM (σ = 2.5%) record performance of the EPI. In pure C3H8 a resolution below σ = 2.0% was reached. Measurements of drift velocities in various Ne mixtures are presented, showing saturated behaviour already at low E/p values.