High Momentum Resolution tracking In a Linear Collider

The Large Hadron Collider (LHC) is in the starting phase of its operation. It is believed that many exciting measurements will be made here. Among other things, it is the hope of the particle physics community that the elusive Higgs Boson will nally be detected here. At the same time, research and development is being conducted towards the next large experiment, which will probably be a linear lepton collider. Such a facility is more suited to conduct precision measurements which are more dicult at a hadron collider. The work in this thesis has been made within the LCTPC-collaboration, an international collaboration for studying the technical aspects af a possible tracking detector at a linear collider. The collaboration has built a prototype Time Projection Chamber (TPC) for testing the properties of dierent readout structures. A TPC is a tracking detector consisting of a gas lled drift volume placed in a solenoidal magnetic eld where the readout is made using a segmented plane of so called pads. When a charged particle traverses the chamber, it ionizes the gas and leaves a trail of electrons which are subjected to an electric eld that makes them drift towards the readout plane where they are collected on the pads. The TPC is capable of 3D tracking, i.e. determining track coordinates in both the drift direction (z) and in the plane perpendicular to this direction (the \bend plane"), as well as momentum and energy loss measurements. This thesis focuses on measurements made using a certain kind of readout structure, Gas Electron Multipliers (GEMs), which promise better performance than previously used techniques. Spatial and momentum resolution are important for a linear collider, and GEMs oer considerable improvement in this area. The measurements were made at the DESY test beam 24 in Hamburg with a 5GeV electron beam. The readout structure made it possible to measure tracks of approximately 50cm in length. Unfortunately, the measurements suered from distortions created by an inhomogeneous electric eld caused by the GEM support structure. A correction for this was attempted using the Millepede method, which allowed an alignment of the recorded particle tracks. Using the corrections, a spatial resolution of y(0) = 590:4m and z(0) = 204 0:9m was obtained for the drift direction and the bend plane respectively. An estimation of the momentum resolution was also obtained, 0:00919 0:00018 GeV􀀀1, which compares well to the goals set for the nal TPC envisaged for the linear collider.