Search for direct pair production of sleptons and charginos decaying to two leptons and neutralinos with mass splittings near the $W$ boson mass in ${\sqrt{s}=13\,}$TeV $pp$ collisions with the ATLAS detector

A search for the electroweak production of charged slepton and chargino pairs decaying into two-lepton final states and with missing transverse momentum is presented. Two simplified models of $R$-parity-conserving supersymmetry are considered: direct pair-production of sleptons ($\tilde{\ell}\tilde{\ell}$) and direct pair-production of lightest charginos $(\tilde{\chi}_1^\pm\tilde{\chi}_1^\mp)$, which decay into $W$ bosons. The lightest neutralino ($\tilde{\chi}_1^0$) is assumed to be the lightest supersymmetric particle (LSP). The analysis targets the mass regions $(m(\tilde{\ell})-m(\tilde{\chi}_1^0))$ and $(m(\tilde{\chi}_1^\pm)-m(\tilde{\chi}_1^0))$ of the order or not too far away from the $W$ boson mass ("moderately compressed" regions). It is based on 139 fb$^{-1}$ of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at $\sqrt{s}=13$ TeV. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the ($\tilde{\ell},\tilde{\chi}_1^0$) and ($\tilde{\chi}_1^\pm,\tilde{\chi}_1^0$) 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 135 GeV are excluded at 95% CL for the case of a mass splitting between the chargino and the LSP up to 100 GeV.