Measurement of the differential cross section of $t\bar{t}$ pairs in $pp$ collision at $\sqrt{s} = 7$ TeV with the ATLAS detector at the LHC

The analysis presented on this thesis is focused on the relative top-anti top production cross section $1/\sigma\frac{d\sigma}{dX}$\footnote{The relative, or normalized, differential cross section is affected by lower systematic errors, since many sources of uncertainty do not modify the shape of the reconstructed distributions, but only their normalization.} as a function of the mass, transverse momentum and rapidity of the system. The topology under study is the single-lepton channel. The analysis has been performed using a cut-based approach: events are been selected in order to reduce the background contribution and enhance the signal-over-background ratio. Once the reconstruced kinematic distribution are extracted, the cross section is calculated in the full phase space at the parton level via unfolding methods.