A drift chamber array for the measurement of electron trajectories

Abstract

This thesis describes an array of eight multi-cell drift chambers, of novel design, user! in the (g-2) Muon Storage Ring at CKUN. The array detected decay electrons traversing an inhomogeneous magnetic field ranging from 14.75 kG to 4 kG over the lengh of the chambers. Data analysis aimed to reconstruct the circulating muon beam profile and determine the decay electron energies. Results from the (g-2) experiment are outlined. The development of drift chambers, the principle of operation and their future uses are discussed. The design considerations and operating parameters of the (g-2) chambers are explained. A gas mixture of argon-methane (90:10) was used in the chambers. The computerized data acquisition system developed at CERN is described in detail. It incorporated a new Drift Time Digitizer system. The data were analysed to produce chamber drift velocity calibrations. Electric equipotential plots were derived to enable the computation of theoretical drift velocities. The existence of variable drift velocities throughout the drift spaces was revealed. Particles traversing the chambers near the cell boundaries were observed to produce recorded drift times at both adjacent sense wires. Analysis of the data in these dual detection regions produced better estimates of the drift velocities which were in good agreement with the theoretical values. An experimental scanning system is outlined which would provide accurate drift velocity calibrations in such complex fields. The performance of the drift chamber array is evaluated and the principles of the track reconstruction outlined. The analysis produced underestimates of the radius of curvature of the circulating muons and the decay electron energies. It is demonstrated that low spatial resolutions due to inaccuracies in the drift velocity calibrations produced such errors. Improvements to the drift chamber design and operating parameters are suggested that would increase the attainable spatial resolution.