Monitoring radiation damage in the vertex locator and top pair production in LHCb

Brown, Henry
Monitoring radiation damage in the vertex locator and top pair production in LHCb. Doctor of Philosophy thesis, University of Liverpool.

The Large Hadron Collider (LHC) is a proton-proton collider at the European Centre for Nuclear Research (CERN). The LHCb experiment is one of the four main experiments at the LHC. It is designed for the detection of bbbar pairs produced in proton-proton collisions and to make precision measurements of B-mesons. The trigger level identification of B-mesons is provided by the Vertex Locator (VELO), which is the primary tracking detector of the experiment. Due to its proximity to the interaction point, the VELO is exposed to high levels of radiation damage. A new method of monitoring the damage is to perform current-voltage (IV) scans and to compare the results of these scans to laboratory tests on sample sensors. A method to perform the first ttbar production measurement in the $\eta>2$ range at the LHC, using a dilepton+b-jet channel, is also presented. A fiducial cross-section is obtained of $\sigma_{\mathrm{fid}}= 24.3^{+14.6}_{-9.7}\mathrm{(stat.)}\pm 6.9\mathrm{(syst.)} \pm 0.9 \mathrm{(lumi.)}$fb, which is consistent with Standard Model expectations. The author's work was to perform the analysis of the IV scans and the comparison to the empirical models obtained in test environments, and to develop the method, as well as the necessary theoretical predictions, for the top pair cross-section measurement.