The Tracker in the Trigger of LHCb

Situated at the LHC, the LHCb experiment is to measure B meson decay with high statistics. Its primary goals are the establishment of CP violation parameters with high precision, and the study of rare B meson decays to look for physics processes beyond the Standard Model. In this thesis, an overview is given on the Outer Tracker (OT) subdetector of the LHCb experiment. The requirements on efficiency, resolution, occupancy and radiation hardness are discussed. The detector design and readout electronics of the OT, a gas filled detector, are presented. To meet the requirements, straw tube cathodes of 4.9mm inner diameter surround the anode wires. The tubes are filled with an Argon based counting gas at atmospheric pressure, allowing for a channel resolution better then 200mum. To limit multiple scattering, the OT is built from lightweight composite materials, resulting in a momentum resolution of dp/p < 0.6% for p between 0 and 150 GeV/c. From extensive ageing tests involving single channels as well as entire prototype modules, the OT seems resistant to particle fluxes up to 60 kHz/cm^2, corresponding to an integrated dose of 100 krad, and accumulated charges of 1.3C/cm straw tube in 10 years of operation. The T stations, consisting of the OT and Inner Tracker subdetectors is used for particle momentum measurement. In this thesis, an algorithm is presented which uses binary responses from the T stations to estimate the momentum of continuations of track segments reconstructed in the VELO. The track finding efficiency is about 90% for tracks with a pT between 0.8 and 10 GeV, the momentum resolution is below 2%.