Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at (Formula presented.) TeV with the ATLAS detector

Searches for electroweak production of wino-like chargino pairs, χ~₁⁺χ~₁⁻, and of wino-like chargino and next-to-lightest neutralino, χ~₁^±χ~₂⁰, are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, χ~₁^±→W^±χ~₁⁰. The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to χ~₁⁰ and either a Z or a Higgs boson, χ~₂⁰→Zχ~₁⁰ or hχ~₁⁰. 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 (Formula presented.) 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 χ~₁⁰ in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless χ~₁⁰ for χ~₂⁰→Zχ~₁⁰. For decays through an on-shell Higgs boson and for mass-splitting between χ~₁^±/χ~₂⁰ and χ~₁⁰ 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.