Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at √s=13 TeV with the ATLAS detector

Searches for electroweak production of wino-like chargino pairs, $\tilde{\chi}^{\pm}_1\tilde{\chi}^{\mp}_1$, and of wino-like chargino and next-to-lightest neutralino, $\tilde{\chi}^{\pm}_1\tilde{\chi}^{0}_2$, are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, $\tilde{\chi}^{\pm}_1\to W^{\pm}\tilde{\chi}^{0}_1$. The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to $\tilde{\chi}^{0}_1$ and either a Z or a Higgs boson, $\tilde{\chi}^{0}_2\to\tilde{\chi}^{0}_1Z$ or $\tilde{\chi}^{0}_2\to\tilde{\chi}^{0}_1h$. The searches exploit the presence of a single isolated lepton and missing transverse momentum from the W boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying Z or W bosons or from the Higgs boson decaying into a pair of b-quarks. The searches use 139 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless $\tilde{\chi}^{0}_1$ in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless $\tilde{\chi}^{0}_1$ for $\tilde{\chi}^{0}_2\to\tilde{\chi}^{0}_1Z$. For decays through an on-shell Higgs boson and for mass-splitting between $\tilde{\chi}^{\pm}_1$ and $\tilde{\chi}^{0}_1$ as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200–260 GeV and 280–470 GeV compared to previous ATLAS constraints.