I. Lehraus

Performance of the ALEPH Time Projection Chamber

Abstract The performance of the ALEPH Time Projection Chamber (TPC) has been studied using data taken during the LEP running periods in 1989 and 1990. After correction of residual distortions and optimisation of coordinate reconstruction algorithms, single coordinate resolutions of 173 μm in the azimuthal and 740 μm in the longitudinal direction are achieved. This results in a momentum resolution for the TPC of Δp / p 2 = 1.2 × 10 −3 (GeV/ c ) −1 . In combination with the ALEPH Inner Tracking Chamber (ITC), a total momentum resolution of Δp / p 2 = 0.8 × 10 −3 (GeV/ c ) −1 is obtained. With respect to particle identification, the detector achieves a resolution of 4.4% for the measurement of the ionisation energy loss.

High energy particle identification using multilayer proportional counters

Abstract An optimised system of proportional counters consisting of 128 layers (32 channels each, 190 × 60 cm 2 detection area) is being developed to work in connection with the Big European Bubble Chamber at SPS energies. It will be capable of identification of simultaneous particles up to 70 GeV/ c by ionization measurements in the region of the relativistic rise. Preliminary tests with a reduced version of 32 layers have been made with pions, kaons and protons at 16 GeV/ c , the results of which are presented.

Performance of a large scale multilayer ionization detector and its use for measurements of the relativistic rise in the momentum range of 20–110 GeV/c

The relativistic rise of ionization has been measured with ±3% fwhm resolution at 20, 30, 40, 50, 64, 70, 90 and 110 GeV/c. The measurements were performed during tests of a large 128 layer proportional detector system (EPI) designed for identification of fast secondary particles in connection with the big hydrogen bubble chamber BEBC. Results of linearity tests of the detector, using X-ray sources, are presented. Factors affecting the long term stability of the detector are analysed and the method used for the off-line data treatment is described.

High-resolution ionization measurements in the region of the relativistic rise

Abstract Results of a 62-layer gas proportional counters test at 9 GeV/ c are given. The achieved resolution in the ionization was 9.4% fwhm for 4 cm layer thickness and Ar + 5% CH 4 gas mixture. The ionization ratio of pions and protons was 1.21±0.01 for argon at atmospheric pressure. Other gas mixtures were also tested. The results of the experiment were used for design improvements of a 128 layer ionization detector proposed for identification of fast secondaries emerging from the 3.7 m bubble chamber working at SPS energies.

dEdx measurements in Ne, Ar, Kr, Xe and pure hydrocarbons

Abstract Ionization sampling resolution and relativistic rise at 15 GeV/c were compared at different pressures in neon, argon, krypton, xenon and pure hydrocarbons, using a detector consisting of 64 samples of 4 cm and a drift space of up to 50 cm. Best results were obtained for π p separation in neon (>6.7σ) and for >e π separation in xenon (>4.8σ). Pure ethylene and propane were comparable to argon mixtures for π p separation, but the corresponding >e π separation suffered from a lower relativistic rise. The signal attenuation by electron attachment was more pronounced in heavier hydrocarbons. Drift velocity measurements are presented and E p limits imposed by requirements of d E d x resolution are discussed.

Calibration of field inhomogeneities in a time projection chamber with laser rays

Abstract We present some results on the use of a set of laser beams to monitor and to measure the systematic displacements of the electron drift trajectories in a Time Projection Chamber of large (0.6 m 3 ) dimensions.

Particle identification by dE/dx sampling in high pressure drift detectors☆

Abstract Resolution limits of large d E /d x sampling detectors were studied systematically for pressures up to 5.5 atm in a variety of argon mixtures. The measurements were performed in a detector consisting of 64 pairs of 2 × 2 cm 2 proportional counters and a 50 cm drift space. Resolving power and linearity of response were measured for several quasi-simultaneous particles at higher pressures, extending the total detector depth to 41 m of NTP equivalent. The results show that resolution is consistently reduced with respect to predictions based on atmospheric pressure measurements for depths up to 7.7 m without drift (EPI detector). Influence of second-order effects and critical parameters affecting the resolution are analyzed with emphasis on compact detector design and relativistic rise region.

External Particle Identifier (EPI) for the Big European Bubble Chamber (BEBC)

Abstract A description of a multi-layer proportional counter system being built to identify fast charged secondary particles behind the 3.7 m bubble chamber is given in detail. The device consists of 128 layers, each with 32 (6×6 cm 2 ) cells across. It will be able to distinguish pions and kaons up to 70 GeV/c by sampling the ionization in the region of the relativistic rise.

The spatial resolution of the ALEPH TPC

The present understanding of the factors which limit the rφ measurement accuracy of the ALEPH time projection chamber is outlined. The resolution for high-momentum tracks is shown to be dominated by the E × B and angular affects.

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 ¿/K/p separation is found to be better in Ne, but extends to higher momenta in Ar. Ar is more efficient for e/¿ 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 (¿ = 2.5%) record performance of the EPI. In pure C3H8 a resolution below ¿ = 2.0% was reached. Measurements of drift velocities in various Ne mixtures are presented, showing saturated behaviour already at low E/p values.