A search for ttbar resonances in lepton+jets events with highly boosted top quarks collected in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

TL;DR

This paper searches for high-mass top-quark pair resonances in proton-proton collisions at 7 TeV using the ATLAS detector, focusing on highly boosted top quarks in the lepton+jets channel, and sets limits on new physics models.

Contribution

It introduces a specialized analysis for highly boosted top quarks in the lepton+jets final state at 7 TeV, providing new constraints on potential resonant top-quark pair production.

Findings

No significant deviation from the Standard Model observed.

Excludes Kaluza-Klein gluons with masses below 1.5 TeV.

Sets upper limits on resonance production cross sections.

Abstract

A search for resonant production of high-mass top-quark pairs is performed on 2.05 fb^-1 of proton-proton collisions at sqrt(s) = 7 TeV collected in 2011 with the ATLAS experiment at the Large Hadron Collider. This analysis of the lepton+jets final state is specifically designed for the particular topology that arises from the decay of highly boosted top quarks. The observed ttbar invariant mass spectrum is found to be compatible with the Standard Model prediction and 95% credibility level upper limits are derived on the ttbar production rate through new massive states. An upper limit of 0.7 pb is set on the production cross section times branching fraction of a narrow 1 TeV resonance. A Kaluza-Klein gluon with a mass smaller than 1.5 TeV is excluded.