Abstract
Results from a search for supersymmetry in events with four or more leptons including electrons, muons and taus are presented. The analysis uses a data sample corresponding to 20.3 $fb^{-1}$ of proton--proton collisions delivered by the Large Hadron Collider at $\sqrt{s}$ = 8 TeV and recorded by the ATLAS detector. Signal regions are designed to target supersymmetric scenarios that can be either enriched in or depleted of events involving the production of a $Z$ boson. No significant deviations are observed in data from Standard Model predictions and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclusion limits at the 95% confidence level on the masses of relevant supersymmetric particles are obtained. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to electrons and muons, limits of 1350 GeV and 750 GeV are placed on gluino and chargino masses, respectively. In R-parity-conserving simplified models with heavy neutralinos decaying to a massless lightest supersymmetric particle, heavy neutralino masses up to 620 GeV are excluded. Limits are also placed on other supersymmetric scenarios.
Highlights
Supersymmetry (SUSY) [1,2,3,4,5,6,7,8,9] is a space-time symmetry that postulates the existence of new SUSY particles, or sparticles, with spin (S) differing by one half-unit with respect to their standard model (SM) partners
The choice of lower bound is guided by the limits from the previous searches at the Large Electron Positron collider (LEP) and the Tevatron; the production cross sections at those values lie between 0.4 pb and 4.5 pb
In all gauge-mediated SUSY breaking (GGM) scenarios the gravitino G~ is the LSP and, unlike GMSB SUSY models, the colored sparticles are not required to be heavier than the electroweak sparticles, which allows for an enhanced discovery potential at the LHC [18,36]
Summary
Supersymmetry (SUSY) [1,2,3,4,5,6,7,8,9] is a space-time symmetry that postulates the existence of new SUSY particles, or sparticles, with spin (S) differing by one half-unit with respect to their standard model (SM) partners. In generic SUSY models with minimal particle content, the superpotential includes terms that violate conservation of lepton (L) and baryon (B) number [10,11]: λijkLiLjEk þ λ0ijkLiQjDk þ λ0i0jkUi. Dk þκiLiH2; ð1Þ where Li and Qi indicate the lepton and quark SU(2)doublet superfields, respectively, while Ei, Ui and Di are. In R-parity-conserving (RPC) models, the lightest SUSY particle (LSP) is stable and leptons can originate from unstable weakly interacting sparticles decaying into the LSP. In RPV models, the LSP is unstable and decays to SM particles, including charged leptons and neutrinos when at least one of the λijk parameters is nonzero Both the RPC and RPV SUSY scenarios can result in signatures with large lepton multiplicities and substantial missing transverse momentum, which can be utilized to suppress.
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