A study of the sensitivity to the Pythia8 parton shower parameters of $t\bar{t}$ production measurements in $pp$ collisions at $\sqrt{s} = 7$ TeV with the ATLAS experiment at the LHC

Various measurements of $t\bar{t}$ observables, performed by the ATLAS experiment in $pp$ collisions at $\sqrt{s} = 7$ TeV, are used to constrain the initial- and final-state radiation parameters of the Pythia8 Monte Carlo. The resulting tunes are compared to previous tunes to the $Z$ boson transverse momentum at the LHC, and to the LEP event shapes in $Z$ boson hadronic decays. Such a comparison provides a test of the universality of the parton shower model. The tune of Pythia8 to the $t\bar{t}$ measurements is applied to the next-to-leading order generators aMC@NLO and Powheg, and additional parameters of these generators are tuned to the $t\bar{t}$ data. For the first time in the context of Monte Carlo tuning, the correlation of the experimental uncertainties has been used to constrain the parameters of the Monte Carlo models.