jats:titleAjats:scbstract</jats:sc> </jats:title>jats:pA search for the electroweak production of pairs of charged sleptons or charginos decaying into two-lepton final states with missing transverse momentum is presented. Two simplified models of jats:italicR</jats:italic>-parity-conserving supersymmetry are considered: direct pair-production of sleptons jats:inline-formulajats:alternativesjats:tex-math$$ \left(\overset{\sim }{\ell}\overset{\sim }{\ell}\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mfenced mml:mrow mml:mover mml:miℓ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mover mml:miℓ</mml:mi> mml:mo~</mml:mo> </mml:mover> </mml:mrow> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula>, with each decaying into a charged lepton and a jats:inline-formulajats:alternativesjats:tex-math$$ {\overset{\sim }{\chi}}_1^0 $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mn0</mml:mn> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> neutralino, and direct pair-production of the lightest charginos jats:inline-formulajats:alternativesjats:tex-math$$ \left({\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_1^{\mp}\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mfenced mml:mrow mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mo±</mml:mo> </mml:msubsup> mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mo∓</mml:mo> </mml:msubsup> </mml:mrow> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula>, with each decaying into a jats:italicW</jats:italic>-boson and a jats:inline-formulajats:alternativesjats:tex-math$$ {\overset{\sim }{\chi}}_1^0 $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mn0</mml:mn> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula>. The lightest neutralino jats:inline-formulajats:alternativesjats:tex-math$$ \left({\overset{\sim }{\chi}}_1^0\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mfenced mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mn0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> is assumed to be the lightest supersymmetric particle (LSP). The analyses target the experimentally challenging mass regions where jats:inline-formulajats:alternativesjats:tex-math$$ m\left(\overset{\sim }{\ell}\right)-m\left({\overset{\sim }{\chi}}_1^0\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mim</mml:mi> mml:mfenced mml:mover mml:miℓ</mml:mi> mml:mo~</mml:mo> </mml:mover> </mml:mfenced> mml:mo−</mml:mo> mml:mim</mml:mi> mml:mfenced mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mn0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> and jats:inline-formulajats:alternativesjats:tex-math$$ m\left({\overset{\sim }{\chi}}_1^{\pm}\right)-m\left({\overset{\sim }{\chi}}_1^0\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mim</mml:mi> mml:mfenced mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mo±</mml:mo> </mml:msubsup> </mml:mfenced> mml:mo−</mml:mo> mml:mim</mml:mi> mml:mfenced mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mn0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> are close to the jats:italicW</jats:italic>-boson mass (‘moderately compressed’ regions). The search uses 139 fbjats:supjats:italic−</jats:italic>1</jats:sup> of jats:inline-formulajats:alternativesjats:tex-math$$ \sqrt{s} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msqrt mml:mis</mml:mi> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 13 TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the jats:inline-formulajats:alternativesjats:tex-math$$ \left(\overset{\sim }{\ell },{\overset{\sim }{\chi}}_1^0\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mfenced mml:mover mml:miℓ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mn0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> and jats:inline-formulajats:alternativesjats:tex-math$$ \left({\overset{\sim }{\chi}}_1^{\pm }{\overset{\sim }{\chi}}_1^0\right) $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mfenced mml:mrow mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mo±</mml:mo> </mml:msubsup> mml:msubsup mml:mover mml:miχ</mml:mi> mml:mo~</mml:mo> </mml:mover> mml:mn1</mml:mn> mml:mn0</mml:mn> </mml:msubsup> </mml:mrow> </mml:mfenced> </mml:math></jats:alternatives></jats:inline-formula> mass planes at 95% confidence level (CL). Sleptons with masses up to 150 GeV are excluded at 95% CL for the case of a mass-splitting between sleptons and the LSP of 50 GeV. Chargino masses up to 140 GeV are excluded at 95% CL for the case of a mass-splitting between the chargino and the LSP down to about 100 GeV.</jats:p>