Inclusive search for same-sign dilepton signatures in pp collisions at s=7 TeV with the ATLAS detector

An inclusive search is presented for new physics in events with two isolated leptons (electron or muon) having the same electric charge. The data are selected from events collected from pp collisions at sqrt(s) = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 inverse picobarns. The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the di-electron, di-muon and electron-muon channels. Four models predicting same-sign dilepton signals are constrained: two descriptions of Majorana neutrinos, a cascade topology similar to supersymmetry or universal extra dimensions, and fourth generation down-type quarks. Assuming a new physics scale of 1 TeV, Majorana neutrinos produced by an effective operator V with masses below 460 GeV are excluded at 95% confidence level. A lower limit of 290 GeV is set at 95% confidence level on the mass of fourth generation down type quarks.

1 August 2011

Contact: Exotics conveners internal

Figures

Figure 01


The selection efficiency for candidates mimicking primary electrons, ϵTLbkge, defined as the fraction of loosely selected electrons that also pass tight selection, measured in a control sample of recorded data and parameterised in \pt\ and \Ht. The events used to determine ϵTLbkge were recorded using a photon trigger, which was prescaled for part of the 2010 pp data collection.

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Figure 02


The selection efficiency for candidates mimicking primary muons, ϵTLbkgμ, defined as the fraction of loosely selected muons that also pass tight selection, parameterised as a function of \pt\ and \Ht.

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Figure 08


Feynman diagram of cascade topology denoted in supersymmetric nomenclature. The analysis is done with WW,ZZ and WZ combinations of weak vector bosons; WZ is shown in the diagram. This topology may also be found in other models such as UED.

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Figure 09


Observed 95\% CL upper cross-section limits [pb] as a function of mχ~1±,χ~20 and mq~ for mχ~10=50 \gev. As an example, we exclude a portion of parameter space (shaded) assuming a gluino mass of 510 \gev\ in order to calculate the cross-section. (This mass value is chosen to be greater than 500 \gev, the largest squark mass considered, but is otherwise arbitrary.) The mix of processes (Equations~???--???) included in the signal model is given in Section~???. The space is sampled in a rough grid (sample points indicated by a ) and the limits are interpolated.

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Figure 12


Expected and observed 95\% CL limits on d4 production cross-section as a function of its mass, compared to limits from CDF~\cite{Aaltonen:2009nr,cdfbprimelj} and CMS~\cite{cms:2011em}.

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