Studies of radiation damage in silicon sensors and a measurement of the inelastic proton--proton cross-section at 13 TeV

This thesis presents studies of radiation damage in silicon sensors for the new ATLAS tracker at the high-luminosity LHC, calibrations of the LHC luminosity scale, and a measurement of the proton--proton inelastic cross-section at 13 TeV~with ATLAS data. The studies of radiation damage are performed by comparing sensor performance before and after irradiation, and include annealing studies. The measured quantities include: leakage current, depletion depth, inter-strip isolation, and charge collection. Surface and bulk damage is studied by comparing the results of sensors irradiated with protons and neutrons. The observed degradation of performance suggests the current sensor design will endure the radiation damage expected over the lifetime of the experiment at the high-luminosity LHC. The luminosity is calibrated for the proton--proton, proton--lead, and lead--lead collisions delivered by the LHC during 2013 and 2015. The absolute luminosity scale is derived with the van der Meer method. The systematic uncertainties on these measurements are 1.9%, 2.7%, and 6.0% respectively. The measurement of the proton--proton inelastic cross-section at ${13~TeV}$~is performed with ${60.1~\mu\mathrm{b}^{-1}}$~of data and an array of plastic scintillators. The luminosity calibration is one of the dominant sources of systematic uncertainty. The result is {$79.3 \pm 2.9~\mathrm{mb}$}. The value is 11% higher than at 7 TeV~and agrees well with theoretical predictions.