Abstract
A search for supersymmetry in events with four or more charged leptons (electrons, muons and τ-leptons) is presented. The analysis uses a data sample corresponding to 139 fb−1 of proton-proton collisions delivered by the Large Hadron Collider at sqrt{s} = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying τ-leptons are designed to target several supersymmetric models, while a general five-lepton signal region targets any new physics phenomena leading to a final state with five charged leptons. Data yields are consistent with Standard Model expectations and results are used to set upper limits on contributions from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge-mediated supersymmetry, excluding higgsino masses up to 540 GeV. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.6 TeV, 1.2 TeV, and 2.5 TeV are placed on wino, slepton and gluino masses, respectively.
Highlights
Background determinationThe SM background is composed of processes that can give rise to four real or fake/nonprompt leptons and these are classified into two categories: Irreducible background: hard-scattering processes giving rise to events with four or more real leptons, ZZ, ttZ, ttW W, ttZZ, ttW Z, ttW H, ttHH, tW Z, V V Z (ZZZ, W ZZ, W W Z), Higgs (H via gluon-gluon fusion (ggF), W H, ZH, H via vector-boson fusion (VBF), ttH), tttt, tttW .Reducible background: processes leading to events with at least one fake/non-prompt lepton, tt, Z+jets, W Z, W W, W W W, ttW, ttt
̃L/ν next-to-lightest SUSY particles (NLSP): mass-degenerate sleptons and sneutrinos of all three generations are produced in association ( ̃LL, νν, ̃Lν, where the subscript L refers to the chirality of the partner lepton)
The SM background is composed of processes that can give rise to four real or fake/nonprompt leptons and these are classified into two categories: Irreducible background: hard-scattering processes giving rise to events with four or more real leptons, ZZ, ttZ, ttW W, ttZZ, ttW Z, ttW H, ttHH, tW Z, V V Z (ZZZ, W ZZ, W W Z), Higgs (H via ggF, W H, ZH, H via VBF, ttH), tttt, tttW
Summary
SUSY is a space-time symmetry that postulates the existence of a new superpartner for every SM particle, with spin differing by one half-unit from its SM partner: each SM fermion (boson) is associated with a SUSY boson (fermion). The bino, wino and higgsino fields are fermionic superpartners of the SU(2) × U(1) gauge fields of the SM, and the two complex scalar doublets of a minimally extended Higgs sector, respectively They mix to give mass eigenstates that are referred to as charginos χ±i (i = 1, 2) and neutralinos χ0j (j = 1, 2, 3, 4), numbered in order of increasing mass. SUSY processes can result in proton decay at a rate that is in conflict with the stringent experimental constraints on the proton lifetime if they do not conserve both lepton number (L) and baryon number (B) [30] This conflict can be avoided by imposing the conservation of R-parity [31], defined as (−1)3(B−L)+2S, where S is spin, or by explicitly conserving either B or L in R-parity-violating (RPV) scenarios [32, 33]. The decoupling limit is used, which is defined by mA mZ, while the CP-odd (A), the neutral CP-even (H), and the two charged (H±) Higgs bosons are considered to be very heavy and considerably beyond the kinematic reach of the LHC
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