Resolution Limits of Ionization Sampling in High Pressure Drift Detectors

Abstract

A systematic study of particle identification performance of full-scale dE/dx sampling detectors including large drift was realized in a device containing 64 pairs of 2 × 2 cm2 proportional cells and a 50 cm drift space. Gas, pressure and drift dependence of the relativistic rise of ionization and mass resolution were measured from 0.5 to 5.5 atm at 15 GeV/c, for mixtures of argon and CH4, C2H4, C2H6, C3H8, iC4H10, CO2, CO2/C2H6, Xe/CH4, Xe/C2H6. Multitrack resolution (linearity of dE/dx response, saturation) was measured for up to 10 quasi-simultaneous particles within a 2 cm diameter beam spot during 1 μs fast spill. The amplitude resolution was found to improve more slowly with pressure (7.5% FWHM was reached at 5.5 atm for 14 m NTP equivalent detector length) than expected from extrapolations of atmospheric pressure measurements without drift. Pressure dependence of signal attenuation in the drift space was smallest in Ar + CH4 mixtures. The results confirm a marked reduction of the relativistic rise slope at higher pressures.

Progress in particle identification by ionization sampling

“…2. shows the truncated mean distributions of lowest 40% values of 64 samples of 4 cm at 1 and 4 atm [31,33] corresponding to single sample distributions from fig. 1.…”

Gaseous Radiation Detectors

“…only determined by the fluctuations in the number of primary ionization encounters. Figure 2.8 (Lehraus et al, 1981) gives an example of energy loss distribution measured with a thin gaseous counter for particles of different mass (protons and electrons) and equal momentum. As expected, the most probable values differ by about 30%, but the distributions largely overlap due to the Landau energy loss statistics.…”

“…As expected, the most probable values differ by about 30%, but the distributions largely overlap due to the Landau energy loss statistics. To achieve particle identification, multi-sampling devices are used to measure many independent segments of the same tracks and combine them with appropriate statistical analysis; a truncated mean algorithm on 64 measured samples results in the distributions shown in Figure 2.9, with a good separation between protons and pions and, to a lesser extent, electrons (Lehraus et al, 1981).…”

“…Model calculations suggested, however, that the primary ionization increase in the relativistic rise region is only a fraction of the total, as shown in Figure 2.15, demonstrating that an important fraction of the relativistic rise is produced by the Figure 2.9 Particle identification resolution obtained from statistical analysis of energy loss measured on 64 track samples (Lehraus et al, 1981). © The Royal Swedish Academy of Sciences.…”

“…Figure 2.8 Experimental energy loss spectra in a thin sample of gas for protons and pions of equal momentum (15 GeV/c)(Lehraus et al, 1981). © The Royal Swedish Academy of Sciences.…”