Measurement of top-quark mass and inclusive top-quark-pair production cross section in pp collisions at √(s)=7/8 TeV with CMS

One of the most intriguing particles in the Standard Model is the top quark, the heaviest fundamental particle known to date. In this thesis, the mass of the top quark and the production cross section for top-quark pairs are measured from events with a top-quark pair decaying only into hadrons. This challenging decay mode features a high rate but is drowned by multijet background events. The top quarks are produced at the Large Hadron Collider and the decay products are detected with the Compact Muon Solenoid experiment. Data collected at centre-of-mass energies of 7 and 8 TeV with integrated luminosities of 3.54 fb-1 and 18.2 fb-1 is used for the presented measurements. In order to improve the reconstruction and identification of the desired events, constrained least-squares fitting is utilised, which exploits the kinematics of top-quark pair events. The top-quark mass and the production cross section for top-quark pairs are extracted using likelihoods from events with at least six jets created from the hadrons in the final state. In order to reduce systematic uncertainties on the result, their main sources are incorporated into the likelihoods and are estimated in parallel with the mass itself. Combining all these methods, the most precise measurement of the top-quark mass from all-jets events so far is achieved. The top-quark mass is measured to be 172.08±0.90 GeV.