Abstract
Abstract A search is presented for same-sign top-quark production and down-type heavy quarks of charge −1/3 in events with two isolated leptons (e or μ) that have the same electric charge, at least two jets and large missing transverse momentum. The data are selected from pp collisions at $ \sqrt {s} = {7}\;{\text{TeV}} $ recorded by the ATLAS detector and correspond to an integrated luminosity of 1.04 fb−1. The observed data are consistent with expectations from Standard Model processes. Upper limits are set at 95 % confidence level on the cross section of new sources of same-sign top-quark pair production of 1.4-2.0 pb depending on the assumed mediator mass. Upper limits are also set on the pair-production cross-section for new heavy down-type quarks; a lower limit of 450 GeV is set at 95 % confidence level on the mass of heavy down-type quarks under the assumption that they decay 100 % of the time to W t.
Highlights
Background from charge misidentificationEvents in which a pair of opposite-sign leptons are produced may be reconstructed as a pair of same-sign leptons if a lepton charge is misidentified
The observed data are consistent with expectations from Standard Model processes
Upper limits are set at 95% confidence level on the cross section of new sources of same-sign top-quark pair production of 1.4-2.0 pb depending on the assumed mediator mass
Summary
The ATLAS detector [18] is a multipurpose detector with precision tracking, calorimetry and muon spectrometry. Precision measurements of the track coordinates are provided by monitored drift tubes over most of the η range. These are supplemented by cathode-strip chambers measuring both the η and φ coordinates for 2.0 < |η| < 2.7 in the innermost endcap muon station. Full event reconstruction and event storage by the data acquisition system, electron candidates must have transverse energy greater than 20 GeV. They must satisfy shower-shape requirements and correspond to an ID track. These triggers reach their efficiency plateau at lepton pT thresholds of 20 GeV for muons and 25 GeV for electrons
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