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.
Highlights
The top quark holds a peculiar position in the Standard Model as the most massive known particle and the only fermion with mass close to the electroweak symmetry breaking scale
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 analysis is performed bosons from on 1.04 f b−1 the of top decays decay√to either a final state electron or muon pp collisions at s = 7 TeV
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
Summary
The top quark holds a peculiar position in the Standard Model as the most massive known particle and the only fermion with mass close to the electroweak symmetry breaking scale. The top quark has a special role in many scenarios that go beyond the Standard Model (SM), many of which predict new particles that decay preferentially to top anti-top quark pairs [1] One such scenario is the Randall-Sundrum model with a single finite extradimension (RS1) where the SM fermions and gauge bosons can propagate in the bulk. In this scenario the observation of the first Kaluza-Klein (KK) excitation of the gluon may be the first indication of the existence of an extra spatial dimension [2]. In the absence of signal, a limit is set on the production cross-section times branching ratio, σB, and this limit is converted into a mass limit on the KK-gluon in the RS1 model
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