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.
A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb
of
TeV proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.
Abstract:The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy √ s = 8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb −1 . No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c ) of approximately 30.
Keywords: Hadron-Hadron Scattering
JHEP04(2015)116The ATLAS collaboration 58
IntroductionSupersymmetry (SUSY) [1][2][3][4][5][6][7][8][9] postulates the existence of particles (sparticles) which differ by half a unit of spin from their Standard Model (SM) partners. The squarks (q L andq R ) and sleptons (˜ L and˜ R ) are the scalar partners of the left-handed and right-handed quarks and leptons, the gluinos (g) are the fermionic partners of the gluons, and the charginos (χ ± i with i = 1, 2) and neutralinos (χ 0 i with i = 1, 2, 3, 4) are the mass eigenstates (ordered from the lightest to the heaviest) formed from the linear superpositions of the SUSY partners of the Higgs and electroweak gauge bosons. An attractive feature of SUSY is that it can solve the SM hierarchy problem [10][11][12][13][14][15] if the gluino, higgsino and top squark masses are not much higher than the TeV scale.If strongly interacting sparticles exist at the TeV scale, they should be accessible at the Large Hadron Collider (LHC). In the minimal supersymmetric extension of the SM such particles decay into jets, possibly leptons, and the lightest sparticle (LSP). If the LSP is stable owing to R-parity conservation [15][16][17][18][19] and only weakly interacting, it escapes detection, leading to missing transverse momentum (p miss T and its magnitude E miss T ) in the final state. In this scenario, the LSP can be a dark-matter candidate. Significant E miss T can also arise in R-parity-violating scenarios in which the LSP decays to final states containing neutrinos or in scenarios where neutrinos are present in the cascade decay chains of the produced sparticles.This paper presents a search with the ATLAS detector [20,21] for SUSY in final states containing jets, at least one isolated lepton (electron or muon) and large E miss T . Different search channels are used in order to cover a broad parameter space: the events are selected by different requirements on the transverse momentum (p T ) of the leptons, either using low-p T leptons (referred to as the "soft" lepton selection), or high-p T leptons (referred to as the "hard" lepton selection). Each of these categories is further subdivided i...
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