Top Quarks and Diamonds

An analysis of proton-proton collision data at a centre-of-mass energy of 8TeV is presented in this thesis. Data were collected with the Compact Muon Solenoid particle detector in 2012. The Standard Model of Particle Physics is probed by measuring the production cross section of top quark pairs in association with a W boson. To identify this rare process from background contributions, a decay channel with two leptons of same-signed electric charge in the final state is selected. The main background processes, stemming from misidentification of leptons, are estimated using a ratio method. Similarly, the yield of background processes originating from mismeasurements of the lepton’s electric charge is estimated. The cross section is measured to be σttW = 170 +90 −80 (stat) +70 −70 (syst) fb with a significance of 1.6 standard deviations over the background-only hypothesis and found to be in agreement with theoretical predictions. In the second part of this dissertation, diamond is studied as an alternative to silicon for tracking detectors. The radiation tolerance of diamond strip sensors, manufactured from industrial grown chemical vapour deposition diamond, is characterised. For this purpose, the diamond samples were irradiated with 800MeV protons, 70MeV protons, and fast neutrons. Between irradiations, the sensors were tested in a hadron beam with a momentum of 120GeV/c. The signal response to charged particles, as measured by the observed pulse height, is reconstructed with multiple algorithms. The resulting pulse height as a function of fluence is fitted using a simple model and radiation damage constants of 1.24 −0.04×10 cm/(p μm), 1.64 +0.25 −0.27 ×10−18 cm/(p μm), and 3.05 +0.27 −0.27 ×10−18 cm/(n μm) are obtained for 800MeV protons, 70MeV protons, and fast neutrons, respectively. Furthermore, the fluence dependence of the energy resolution and spatial resolution of the diamond strip detectors are measured.