3, the m ℓ ℓ shape in the wino/bino model depends on the relative sign of the χ ˜ 1 0 and χ ˜ 2 0 mass parameters. For Higgsino production, the chargino χ ˜ 1 ± mass is assumed to be halfway between the χ ˜ 2 0 and χ ˜ 1 0 masses, while m ( χ ˜ 2 0 ) = m ( χ ˜ 1 ± ) is assumed for the wino/bino model. A fit of signals to the m ℓ ℓ spectrum is used to derive the limit, which is projected into the Δ m ( χ ˜ 2 0, χ ˜ 1 0 ) vs m ( χ ˜ 2 0 ) plane. exclusion sensitivity (blue dashed line), with ± 1 σ exp (yellow band) from experimental systematic uncertainties and statistical uncertainties on the data yields, and observed limits (red solid line) with ± 1 σ theory (dotted red line) from signal cross-section uncertainties for simplified models of direct Higgsino (top) and wino (bottom) production.
The individual uncertainties can be correlated and do not necessarily add up in quadrature to the total uncertainty.
All sources of uncertainty affecting the FNP background estimate are included under “Fake/nonprompt.” The uncertainties arising from the reconstruction and selection of signal leptons, jets, and E T miss are included under the “Experimental” category. The “Normalization” uncertainty arises from the use of CRs to normalize the contributions of t t ¯ / t W, Z ( * ) / γ * ( → τ τ ) + jets and W W / W Z backgrounds, while “Background modeling” includes the different sources of theoretical modeling uncertainties in the m ℓ ℓ or m T 2 100 line shapes for the irreducible backgrounds. The “MC Statistics” uncertainty originates from the limited size of the MC samples used to model the irreducible background contributions.
The uncertainty in the “SS data” includes a statistical component due to the size of the SS data sample used to estimate the background in the SR-E- 1 ℓ 1 T region, and a systematic component from the SS–OS extrapolation. The relative systematic uncertainties in the fitted SM background as obtained from CR + SR background-only fits for the electroweakino SRs (top), VBF SRs (middle), and slepton SRs (bottom). Constraints on vector-boson fusion production of electroweak SUSY states are also presented. Similar lower limits on degenerate light-flavor sleptons extend up to masses of 251 GeV and down to mass splittings of 550 MeV.
Lower limits on the masses of charginos in different simplified models range from 193 to 240 GeV for moderate mass splittings, and extend down to mass splittings of 1.5 to 2.4 GeV at the LEP chargino bounds (92.4 GeV). The results are interpreted using simplified models of R-parity-conserving supersymmetry in which the lightest supersymmetric partner is a neutralino with a mass similar to the lightest chargino, the second-to-lightest neutralino, or the slepton. The data are found to be consistent with predictions from the Standard Model. Events with missing transverse momentum and two same-flavor, oppositely charged, low-transverse-momentum leptons are selected, and are further categorized by the presence of hadronic activity from initial-state radiation or a topology compatible with vector-boson fusion processes. The searches use 139 fb − 1 of s = 13 TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider. This paper presents results of searches for the electroweak production of supersymmetric particles in models with compressed mass spectra.
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