Etude d'un système de trajectographie Micromegas pour le spectromètre dimuon d'ALICE

ALICE (A Large Ion Collider Experiment) will be the only LHC (Large Hadron Collider) experiment dedicated to the study of ultra-relativistic heavy ion collisions at CERN. Related to the design of this detector at Subatech, an R and D program has been carried out on the ALICE dimuon spectrometer tracking chambers using Micromegas detectors. The first aim of this work was to study the performances of this kind of strip detector and to validate their integration feasibility in the spectrometer tracking system. Simulations of the tracking system have exhibit the necessity of an intrinsic two dimensional localization capability, leading to the development of resistive strips for these detectors. With an Ar/CO2 gas mixture and a gain of 104, laboratory and in-beam tests at PS (CERN) have given an efficiency better than 95 pc and an energy resolution of 20 pc. Perpendicular to the strips, a spatial resolution of 43 μm has been obtained using the charge barycentre reconstruction. Along the strip, the charge division of the avalanche signal at both ends of the resistive strips leads to a linear reconstruction of the impact position. Depending on the signal to noise ratio, 1.1 mm to 500 μm spatial resolutions have been obtained. (author)