Measurement of ttbar differential cross-section for highly boosted top quarks produced at ATLAS in pp collisions at sqrt(s) = 8 TeV

The measurement of the differential cross-section for top quark pair production as function of top transverse momentum will be presented. The used dataset has been collected in 2012 in proton-proton collisions at a center of mass energy of 8 TeV. The measurement is performed for $t\bar{t}$ events in the semileptonic channel decay where the hadronically decaying top quark has a transverse momentum above 300 GeV. The hadronic top quark decay is reconstructed as a single large radius jet and identified using the jet substructure properties. This technique allows to increase the detection efficiency extending the cross-section measurement to high $p_T$ region never reached before. The main background sources are evaluated both with data driven methods (for W+jets and fake leptons contributions) and using Monte Carlo simulations (Z+jets, diboson, $t\bar{t}$ dilepton channel, single top). The observed yield, after the background subtraction, is corrected for efficiency and resolution effects to obtain the result both in a fiducial region close to the event selection and also extrapolated to the full partonic phase-space. The final differential cross section has been compared with several theoretical predictions that generally slightly exceed the measured distribution.