C. Lippmann

The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events

The design, construction, and commissioning of the ALICE Time-Projection Chamber (TPC) is described. It is the main device for pattern recognition, tracking, and identification of charged particles in the ALICE experiment at the CERN LHC. The TPC is cylindrical in shape with a volume close to 90 m(3) and is operated in a 0.5T solenoidal magnetic field parallel to its axis. In this paper we describe in detail the design considerations for this detector for operation in the extreme multiplicity environment of central Pb-Pb collisions at LHC energy. The implementation of the resulting requirements into hardware (field cage, read-out chambers, electronics), infrastructure (gas and cooling system, laser-calibration system), and software led to many technical innovations which are described along with a presentation of all the major components of the detector, as currently realized. We also report on the performance achieved after completion of the first round of stand-alone calibration runs and demonstrate results close to those specified in the TPC Technical Design Report

Detector physics and simulation of resistive plate chambers

We present a simulation model suited to study efficiency, timing and pulse-height spectra of Resistive Plate Chambers. After discussing the details of primary ionisation, avalanche multiplication, signal induction and frontend electronics, we apply the model to timing RPCs with time resolution down to 50 ps and trigger RPCs with time resolution of about 1 ns: r 2003 Elsevier Science B.V. All rights reserved. PACS: 07.05.Tp; 29.40.Cs; 29.40.Gx

Static electric fields in an infinite plane condenser with one or three homogeneous layers

Expressions for the electrostatic field of a point charge in an infinite plane condenser comprising one or three homogeneous isolating parallel dielectric layers are presented. These solutions are essential for detector physics simulations of parallel plate chambers and resistive plate chambers. In addition, expressions for the weighting field of a strip electrode are presented which allow calculation of induced signals and crosstalk in these detectors. A detailed discussion of the derivation of these solutions can be found in [Heubrandtner et al. (CERN-OPEN-2001-074, CERN, October 2001)].

Detailed Models for Timing and Efficiency in Resistive Plate Chambers

We discuss detailed models for detector physics processes in Resistive Plate Chambers, in particular including the effect of attachment on the avalanche statistics. In addition, we present analytic formulas for average charges and intrinsic RPC time resolution. Using a Monte Carlo simulation including all the steps from primary ionization to the front-end electronics we discuss the dependence of efficiency and time resolution on parameters like primary ionization, avalanche statistics and threshold.

Space charge effects and induced signals in resistive plate chambers

Abstract Using special integral representations of the solution for the static electric field of a point charge in a three layer geometry with different permittivities, we calculate the effect of the space charge on the avalanche in the gas gap of an RPC. A detailed Monte Carlo simulation was developed which allows calculation of the actual charge spectrum. Results of this simulation are presented, using the example of a trigger-RPC with 2 mm gas gap, similar to the ones used by ATLAS (ATLAS TDR 10, CERN-LHCC-97-22), and a timing RPC with 300 μm gas gap (Nucl. Instr. and Meth. A 449 (2000) 295). Finally, we also present analytic solutions for the weighting field of an RPC readout strip, which allow to calculate the directly induced crosstalk and induced signals.

Position reconstruction in drift chambers operated with Xe, CO2 (15%)

Abstract We present measurements of position and angular resolution of drift chambers operated with a Xe, CO 2 (15%) mixture. The results are compared to Monte Carlo simulations and important systematic effects—in particular the dispersive nature of the absorption of transition radiation and non-linearities—are discussed. The measurements were carried out with prototype drift chambers of the ALICE Transition Radiation Detector, but our findings can be generalized to other drift chambers with similar geometry, where the electron drift is perpendicular to the wire planes.

Simulation of space charge effects in resistive plate chambers

Multigap resistive plate chambers with 0.3-mm gas gaps operated in avalanche mode at atmospheric pressure have reached timing accuracies below 50 ps (standard deviation) with efficiencies above 99% . The avalanches in high homogeneous electric fields of 100 kV/cm are strongly influenced by space charge effects which are the main topic of this paper. We extend a previously discussed Monte Carlo simulation model of avalanches in resistive plate chambers by the dynamic calculation of the electric field in the avalanches. We complete the previously presented results on time resolution and efficiency data with simulated charge spectra. The simulated data shows good agreement with measurements. The detailed simulation of the avalanche saturation due to the space charge fields explains the small observed charges, the shape of the spectra, and the linear increase of average charges with high voltage.