| Large Hadron Collider (LHC) is a top quark factory, which is the heaviest elementary particle discovered so far. Due to its small life-time top quark decays before hadronization, and hence most of its properties are not washed out. Top quark events are often a large background in many beyond the Standard Model scenarios. For this reason, a deep knowledge of its properties and behavior is of crucial importance in searches for new physics at the LHC. This dissertation describes a measurement of the top anti-top pair production cross-section in tau + jets channel. The measurement is obtained by using 4.7 fb-1 data collected in year 2011 by ATLAS detector from proton proton (pp) collisions at the center of mass energy s = 7 TeV. Selected events are required to have one isolated tau with missing transverse energy and hadronic jets, at least one of which must be originated from a b quark. The measured cross section is 152 +/- 12 (stat.) +28-30 (syst.); +/- 3(lumi.) pb, which is in agreement with standard model predictions. |
