Abstract
A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb$^{-1}$ of integrated luminosity taken in 2012 at a centre-of-mass energy of 8 TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type $e^{\pm}e^{\pm}, e^{\pm}\mu^{\pm}$, and $\mu^{\pm}\mu^{\pm}$ are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross-sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production.
Highlights
Background and signal simulationMonte Carlo (MC) simulations are used to estimate the background contributions and to model hypothetical signal events
The expected and observed numbers of events for several cuts on the dilepton mass for each final state are given in table 5, which shows the contributions from the different background types
Other contributions are from ZZ and W ±W ± production and a very small fraction comes from the ttW and ttZ production or from diboson production in multiple parton interactions (MPI) processes
Summary
From the inside to the outside, the ATLAS detector comprises an inner tracking detector (ID), electromagnetic and hadronic calorimeters, and a muon spectrometer (MS). The ID is embedded in a 2 T axial magnetic field produced by a superconducting solenoid and provides precision tracking within the pseudorapidity range |η| < 2.5. It consists of a silicon pixel detector, a semiconductor tracker (SCT) using silicon microstrip detectors, and, in the region |η| < 2, a transition-radiation straw tube tracker (TRT). The first level is implemented in custom electronics, and is followed by two software-based trigger levels This system selects from the collision rate of around 20 MHz about 400 Hz of events to be recorded for physics analyses. More details about the detector and the trigger system can be found elsewhere [25]
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