Bonn 2010 – scientific programme

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T: Fachverband Teilchenphysik

T 38: Top-Quarks IV

T 38.5: Talk

Thursday, March 18, 2010, 17:45–18:00, HG Aula

Event Shapes in tt and QCD Events with ATLAS — •Martin Härtig — Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München

Event Shapes are an efficient way to describe the final state in a collision experiment, used with great success at e⁺−e⁻ colliders. For our analysis of p−p collisions observed with ATLAS, a set of Event Shapes was implemented and tested for sensitivity towards discriminating tt events from QCD and W+jets background events. The resulting implementation of Event Shapes in a multivariate toolkit package hinted that background rejection efficiencies of ∼90% are possible with signal efficiencies above 50% in the full hadronic decay channel, where both figures are relative to a preselection. Finally, we are currently implementing a method to obtain the signal Event Shape distribution by applying a matrix method to the binned distribution of mixed signal+background Event Shapes. By taking the actual event rates from data, this method tries to circumvent uncertainties in the Monte Carlo generators.