Abstract
This paper presents results of searches for electroweak production of supersymmetric particles in models with compressed mass spectra. The searches use 139 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider. 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 data are found to be consistent with predictions from the Standard Model. 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. Lower limits on the masses of charginos in different simplified models range from 193 GeV to 240 GeV for moderate mass splittings, and extend down to mass splittings of 1.5 GeV to 2.4 GeV at the LEP chargino bounds (92.4 GeV). Similar lower limits on degenerate light-flavor sleptons extend up to masses of 251 GeV and down to mass splittings of 550 MeV. Constraints on vector-boson fusion production of electroweak SUSY states are also presented.
Highlights
Extensions of the Standard Model (SM) that include new states with nearly degenerate masses can help to resolve open issues in particle physics while evading constraints from experiments at high-energy colliders
This paper presents searches for physics beyond the SM in signatures sensitive to models with compressed mass spectra
The third scenario is similar to the previous two, but it instead assumes that the pair production of the electroweakinos proceeds via vector-boson fusion (VBF) processes, in which SM weak bosons exchange an electroweakino in a t-channel process to produce two electroweakinos and a pair of forward jets
Summary
Extensions of the Standard Model (SM) that include new states with nearly degenerate masses can help to resolve open issues in particle physics while evading constraints from experiments at high-energy colliders. The third scenario is similar to the previous two, but it instead assumes that the pair production of the electroweakinos proceeds via vector-boson fusion (VBF) processes, in which SM weak bosons exchange an electroweakino in a t-channel process to produce two electroweakinos and a pair of forward jets Such scenarios typically have very low cross sections, but they can complement the sensitivity of qqannihilation modes that dominate the inclusive Higgsino and wino/bino cross sections, especially for LSP masses above a few hundred GeV [25]. The fourth scenario assumes the presence of scalar partners of the SM leptons (sleptons, l ) that are slightly heavier than a bino-like LSP Such models can explain dark-matter thermal-relic densities through coannihilation channels, as well as the muon g − 2 anomaly [26,27]. The dedicated search for production via VBF is added, and the event selection is reoptimized and uses techniques based on recursive jigsaw reconstruction [46], which improve the separation of the SUSY signal from the SM backgrounds
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