Measurement of Top-Quark Pair Production Cross Sections and Calibration of the Top-Quark Monte-Carlo Mass using LHC Run I Proton-Proton Collision Data at $\sqrt{s}=$ 7 and 8 TeV with the CMS Experiment.

In this thesis, measurements of the production cross sections for top-quark pairs andthe determination of the top-quark mass are presented. Dileptonic decays of top-quarkpairs (tt) with two opposite-charged lepton (electron and muon) candidates in the finalstate are considered. The studied data samples are collected in proton-proton collisionsat the CERN Large Hadron Collider with the CMS detector and correspond to inte√grated luminosities of 5.0 fb−1 and 19.7 fb−1 at center-of-mass energies of s = 7 TeV and√s = 8 TeV, respectively. The cross sections, σtt , are measured in the fiducial detectorvolume (visible phase space), defined by the kinematics of the top-quark decay products,and are extrapolated to the full phase space. The visible cross sections are extracted in asimultaneous binned-likelihood fit to multi-differential distributions of final-state observables, categorized according to the multiplicity of jets associated to b quarks (b jets) andother jets in each event. The fit is performed with emphasis on a consistent treatmentof correlations between systematic uncertainties and taking into account features of thett event topology. By comparison with predictions from the Standard Model at nextto-next-to leading order (NNLO) accuracy, the top-quark pole mass, mpole , is extractedtfrom the measured cross sections for different state-of-the-art PDF sets.Furthermore, the top-quark mass parameter used in Monte-Carlo simulations, mMC ,tis determined using the distribution of the invariant mass of a lepton candidate and theleading b jet in the event, mlb . Being defined by the kinematics of the top-quark decay,this observable is unaffected by the description√ the top-quark production mechanism.ofEvents are selected from the data collected at s = 8 TeV that contain at least two jetsand one b jet in addition to the lepton candidate pair. A novel technique is presented,in which fixed-order calculations in quantum chromodynamics (QCD) are employed todetermine the top-quark mass from the shape of the measured mlb distribution.The analysis is extended to a simultaneous fit of the tt production cross sections andMCmt , including the mlb distribution to increase the sensitivity to mMC . The resulting ttt√production cross sections at s = 7 and 8 TeV do not depend on assumptions on mMCtand are the most precise ones obtained with the CMS experiment. The extracted mMCtreaches an unprecedented precision for a single measurement of mMC in the dileptonictdecay channel. The measured σtt are further used to determine mpole and the MS mass,tMSMSmt , at up to NNLO QCD. The extracted mt exhibits a better perturbative convergenceand is converted to the pole mass, mp,conv , using recent calculations at 4-loop QCD.tFor the first time, the direct relation of mMC to mMS , mpole , and mp,conv is quantifiedttttexperimentally at the highest available precision.