P. Igo-Kemenes

Particle identification with the OPAL jet chamber

The jet chamber of the OPAL experiment at the e+e−-collider LEP is designed to measure the momentum of charged particles as well as the specific energy loss in the chamber gas. In this paper, the calibration procedure for the energy loss measurement is described in detail. A resolution of 3–4% has been achieved allowing identification of particles with momenta up to 20 GeV/c in dense particle environments typical for events from Z0 decays.

Performance of the OPAL jet chamber

Abstract The jet chamber of the OPAL experiment at the LEP e + e − collider is designed to measure the direction and the momentum of charged particles as well as the specific energy loss in the chamber gas. The jet chamber has been operated at LEP since August 1989 and has recorded 500 000 hadronic decays of the Z 0 , resulting in a good understanding of the stability and systematics of the chamber. Resolutions obtained in the measurement of particle direction, momentum, and specific energy loss are presented, as well as the corrections and calibration procedures necessary to attain original design goals. A momentum resolution of 6.8% for particles with a momentum of 45 GeV/ c and an energy loss resolution of 3–4% over all momenta have been achieved.

The OPAL jet chamber full scale prototype

Abstract The concept of a jet chamber for the central detector of OPAL has been tested with a full scale prototype. The design of this prototype, its mechanical and electrical structure and its support system for high voltage, gas, laser calibration and readout are described. Operating experience has been gathered since summer 1984. The chamber performance in terms of spatial resolution and particle identification capability is given.

The Opal Jet Chamber

Abstract The characteristic features of the OPAL jet chamber are described, such as the mechanical and electrical structure, the readout electronics, the gas system, and the laser setup for calibration. Results on spatial resolution and on particle identification power, obtained with a full scale prototype chamber, are presented which show that in the final chamber the anticipated performance can be reached.

Electron attachment to oxygen, water, and methanol, in various drift chamber gas mixtures

Abstract Attachment of electrons to oxygen, water, and methanol molecules has been studied in various gas mixtures based on argon, methane and isobutane, a class of gases often used to operate large drift chambers. The measurements were performed using a drift chamber in which the conditions prevailing in large experiments could be closely reproduced. Attachment coefficients were extracted as a function of the gas composition and pressure, the drift field, and the concentration of the molecules under investigation. The observed effects are compared to other measurements, and are discussed within the frame of physical models.

Particle identification with the opal jet chamber in the region of the relativistic rise

Abstract An important goal of the OPAL jet chamber is particle identification at high momenta by exploiting the relativistic rise of the energy loss. Extensive tests have been performed with the full scale prototype of the OPAL jet chamber to measure the energy loss in an argon-methane-isobutane mixture as function of momentum and particle species. The measurements were done under various operating conditions in order to optimise the operating point, to investigate sources of systematic errors, to monitor the stability of the energy loss measurement and to develop calibration procedures. The particle separation capability in the region of the relativistic rise has been studied at gas pressures of 3 and 4 bar. The adopted operating point represents a reasonable compromise between the requirements for particle identification and tracking accuracy.

Investigation of very long jet chambers

The electrostatic properties and the performances of very long jet chambers have been investigated. Using 100 MHz FADC wave form digitisers, the tracking accuracy, the charge division and the dEdx performance of two chambers, one with 4.5 m long tungsten wires and one with 4 m long highly resistive “NiCoTi” wires have been studied. The geometry of the chambers was chosen to define some of the design parameters of the jet chamber for the OPAL detector for LEP.