The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for largescale production of events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions, through packages simulating the response of the various detectors and triggers. All of these components come together under the AT-LAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors. Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output against known physics processes.

A search is conducted for new resonant and non-resonant high-mass phenomena in dielectron and dimuon final states. The search uses 36.1 fb −1 of proton-proton collision data, collected at √ s = 13 TeV by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% credibility level are set on the cross-section times branching ratio for resonances decaying into dileptons, which are converted to lower limits on the resonance mass, up to 4.1 TeV for the E 6 -motivated Z χ . Lower limits on the qq contact interaction scale are set between 2.4 TeV and 40 TeV, depending on the model. Conclusion 21A Dilepton invariant mass tables 22The ATLAS collaboration 44 IntroductionThis article presents a search for resonant and non-resonant new phenomena, based on the analysis of dilepton final states (ee and µµ) in proton-proton (pp) collisions with the ATLAS detector at the Large Hadron Collider (LHC) operating at √ s = 13 TeV. The data set was collected during 2015 and 2016, and corresponds to an integrated luminosity of 36.1 fb −1 . In the search for new physics carried out at hadron colliders, the study of -1 - JHEP10(2017)182dilepton final states provides excellent sensitivity to a large variety of phenomena. This experimental signature benefits from a fully reconstructed final state, high signal-selection efficiencies and relatively small, well-understood backgrounds, representing a powerful test for a wide range of theories beyond the Standard Model (SM).Models with extended gauge groups often feature additional U(1) symmetries with corresponding heavy spin-1 bosons. These bosons, generally referred to as Z , would manifest as a narrow resonance through its decay, in the dilepton mass spectrum. Among these models are those inspired by Grand Unified Theories, which are motivated by gauge unification or a restoration of the left-right symmetry violated by the weak interaction. Examples considered in this article include the Z bosons of the E 6 -motivated [1,2] theories as well as Minimal models [3]. The Sequential Standard Model (SSM) [2] is also considered due to its inherent simplicity and usefulness as a benchmark model. The SSM manifests a Z SSM boson with couplings to fermions equal to those of the SM Z boson.The most sensitive previous searches for a Z boson decaying into the dilepton final state were carried out by the ATLAS and CMS collaborations [4,5]. Using 3.2 fb −1 of pp collision data at √ s = 13 TeV collected in 2015, ATLAS set a lower exclusion limit at 95% credibility level (CL) on the Z SSM pole mass of 3.4 TeV for the combined ee and µµ channels. Similar limits were set by CMS using the 2015 data sample.This search is also sensitive to a series of other models that predict the presence of narrow dilepton resonances. These models include the Randall-Sundrum (RS) model [6] with a warped extra dimension giving rise to spin-2 graviton excitations, the quantum black-hole model [7], the Z * model [8], and the minimal wal...

During 2015 the ATLAS experiment recorded of proton–proton collision data at a centre-of-mass energy of . The ATLAS trigger system is a crucial component of the experiment, responsible for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton–proton collision data.

Search for high-mass dilepton resonances using139 fb −1 of p p collision data collected at √ s = 13 TeV with the ATLAS detectorThe ATLAS Collaboration A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6 TeV is presented. The data were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of √ s = 13 TeV during Run 2 of the Large Hadron Collider and correspond to an integrated luminosity of 139 fb −1 . A functional form is fitted to the dilepton invariant-mass distribution to model the contribution from background processes, and a generic signal shape is used to determine the significance of observed deviations from this background estimate. No significant deviation is observed and upper limits are placed at the 95% confidence level on the fiducial cross-section times branching ratio for various resonance width hypotheses. The derived limits are shown to be applicable to spin-0, spin-1 and spin-2 signal hypotheses. For a set of benchmark models, the limits are converted into lower limits on the resonance mass and reach 4.5 TeV for the E 6 -motivated Z ψ boson. Also presented are limits on Heavy Vector Triplet model couplings.ATLAS [14-16] is a multipurpose detector with a forward-backward symmetric cylindrical geometry with respect to the LHC beam axis.1 The innermost layers consist of tracking detectors in the pseudorapidity range |η| < 2.5. This inner detector (ID) is surrounded by a thin superconducting solenoid that provides a 1 ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector and the z-axis along the beam pipe. The x-axis points from the IP to the centre of the LHC ring, and the y-axis points upwards. Cylindrical coordinates (r, φ) are used in the transverse plane, φ being the azimuthal angle around the z-axis. The pseudorapidity is defined in terms of the polar angle θ as η = − ln tan(θ/2). Angular distance is measured in units of ∆R ≡ (∆η) 2 + (∆φ) 2 .

Searches for the electroweak production of charginos, neutralinos and sleptons in final states characterized by the presence of two leptons (electrons and muons) and missing transverse momentum are performed using 20.3 fb −1 of proton-proton collision data at √ s = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider.No significant excess beyond Standard Model expectations is observed. Limits are set on the masses of the lightest chargino, next-to-lightest neutralino and sleptons for different lightest-neutralino mass hypotheses in simplified models. Results are also interpreted in various scenarios of the phenomenological Minimal Supersymmetric Standard Model.Keywords: Supersymmetry, Hadron-Hadron Scattering The ATLAS collaboration 33 IntroductionSupersymmetry (SUSY) [1][2][3][4][5][6][7][8][9] is a spacetime symmetry that postulates for each Standard Model (SM) particle the existence of a partner particle whose spin differs by one-half unit. The introduction of these new particles provides a potential solution to the hierarchy problem [10][11][12][13]. If R-parity is conserved [14][15][16][17][18], as is assumed in this paper, SUSY particles are always produced in pairs and the lightest supersymmetric particle (LSP) emerges as a stable dark-matter candidate.-1 - JHEP05(2014)071The charginos and neutralinos are mixtures of the bino, winos and higgsinos that are superpartners of the U(1), SU(2) gauge bosons and the Higgs bosons, respectively. Their mass eigenstates are referred to asχ ± i (i = 1, 2) andχ 0 j (j = 1, 2, 3, 4) in the order of increasing masses. Even though the gluinos and squarks are produced strongly in pp collisions, if the masses of the gluinos and squarks are large, the direct production of charginos, neutralinos and sleptons through electroweak interactions may dominate the production of SUSY particles at the Large Hadron Collider (LHC). Such a scenario is possible in the general framework of the phenomenological minimal supersymmetric SM (pMSSM) [19][20][21]. Naturalness suggests that third-generation sparticles and some of the charginos and neutralinos should have masses of a few hundred GeV [22,23]. Light sleptons are expected in gauge-mediated [24][25][26][27][28][29] and anomaly-mediated [30,31] SUSY breaking scenarios. Light sleptons could also play a role in the co-annihilation of neutralinos, allowing a dark matter relic density consistent with cosmological observations [32,33]. This paper presents searches for electroweak production of charginos, neutralinos and sleptons using 20.3 fb −1 of proton-proton collision data with a centre-of-mass energy √ s = 8 TeV collected at the LHC with the ATLAS detector. The searches target final states with two oppositely-charged leptons (electrons or muons) and missing transverse momentum. Similar searches [34,35] SUSY scenariosSimplified models [42] are considered for optimization of the event selection and interpretation of the results. The LSP is the lightest neutralinoχ 0 1 in all SUSY scenarios considered, except in...