Momentum bias determination in the tracker alignment and first differential $t \bar{t}$ cross section measurement at CMS

This thesis is prepared within the framework of the CMS experiment at the Large Hadron Collider. It is divided into a technical topic and an analysis. In the technical part, a method is developed to validate the alignment of the tracker geometry concerning biases in the momentum measurement. The method is based on the comparison of the measured momentum of isolated tracks and the corresponding energy deposited in the calorimeter. Comparing positively and negatively charged hadrons, the twist of the tracker is constrained with a precision of z = 12 rad m . The analysis deals with cross section measurements in events containing an isolated muon and jets. The complete dataset of proton-proton collisions at a centreof- mass energy of 7TeV taken in 2010 is investigated. This corresponds to an integrated luminosity of 35.9 pb􀀀1. Cross sections including dierent physics processes with an isolated muon and jets in the nal state are measured for dierent jet multiplicities (Njets 1; 2; 3; 4). With increasing jet multiplicity, the transition from a W ! l dominated to a strongly tt enriched phase space becomes evident. The inclusive cross section for tt production derived from the four jet sample is measured to be = 172 15(stat.) 41(syst.) 7(lumi.) pb. Cross sections dierentially in kinematic quantities of the muon, d dpT , d d , are measured as well and compared to theoretical predictions.