A search for ttbar resonances in the dilepton channel in 1.04/fb of pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

TL;DR

This paper reports a search for high-mass top pair resonances in dilepton final states at the LHC using ATLAS data, setting limits on new particle production and excluding certain models.

Contribution

First ATLAS analysis searching for top pair resonances in dilepton channel at 7 TeV, setting new exclusion limits on KK-gluon masses.

Findings

No significant excess observed over Standard Model predictions.

Excluded KK-gluon masses below 840 GeV at 95% confidence level.

Set upper limits on production cross-section times branching ratio.

Abstract

The first ATLAS result on a search for a high mass top pair resonance at the LHC, in the subset of events where both W bosons from the top decays decay to either a final state electron or muon, is presented. The analysis is performed on 1.04/fb of pp collisions at sqrt(s) = 7 TeV. Numerous models predict the production of new massive particles that decay preferentially to a top-anti-top pair, including Randall-Sundrum models where the observation of a Kaluza-Klein excitation of the gluon may be the first indication of the existence of an extra spatial dimension. In the analysis presented, a simple observable, sensitive to resonance mass, is formed by summing the missing transverse energy, and the transverse momenta of the selected jets and the two candidate leptons. A deviation from the Standard Model prediction for this observable is searched for using Bayesian statistical methods that compare the yields, and shapes, of the Standard Model background and signal predictions for KK-gluons with masses between 500 and 1600 GeV. No excess over the Standard Model is observed and 95% C.L. upper limits are set on the production cross-section times branching ratio to top quarks for KK-gluon-like resonances. The results of the analysis exclude Randall-Sundrum KK-gluons with masses less than 840 GeV.