Search for cascade decays of charged sleptons and sneutrinos in final states with three leptons and missing transverse momentum in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This ATLAS study investigates cascade decays of charged sleptons and sneutrinos in final states with three leptons and missing momentum, using 140 fb$^{-1}$ of $ ext{pp}$ data at $ oot extsuperscript{$ ext{-}$}{s}=13$ TeV. It targets the SBH model with a higgsino LSP and an intermediate bino-like state, deploying three signal regions to capture on-shell and off-shell boson decays and a same-sign leptons region to enhance sensitivity. No significant excess over SM expectations is observed; consequently, 95% CL limits exclude left-handed sleptons and sneutrinos up to about 450 GeV for $m( ilde{ ilde{ u}}, ilde{ ilde{ u}})=100$ GeV in the Δ$m( ilde{ ilde{ ilde{}}_{3}}, ilde{ ilde{ ilde{}}_{1}}) ext{ region}$, with the strongest bound yielding $m( ilde{ ilde{ ilde{}}_{1}}) ightarrow 205$ GeV at specific mass splittings. This result extends sensitivity to SBH-like scenarios and provides valuable constraints in the electroweakino-slepton sector relevant to muon $(g-2)$ and dark matter considerations.

Abstract

A search for cascade decays of charged sleptons and sneutrinos using final states characterized by three leptons (electrons or muons) and missing transverse momentum is presented. The analysis is based on a dataset with 140 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of $\sqrt{s}$=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. This paper focuses on a supersymmetric scenario that is motivated by the muon anomalous magnetic moment observation, dark mattter relic density abundance, and electroweak naturalness. A mass spectrum involving light higgsinos and heavier sleptons with a bino at intermediate mass is targeted. No significant deviation from the Standard Model expectation is observed. This search enables to place stringent constraints on this model, excluding at the 95% confidence level charged slepton and sneutrino masses up to 450 GeV when assuming a lightest neutralino mass of 100 GeV and mass-degenerate selectrons, smuons and sneutrinos.

Figures (17)

• Figure 1: The neutralino-smuon loop yielding a sizable muon anomalous magnetic moment. The black dot represents the mixing between electroweakinos.
• Figure 2: The mass spectrum and the decay pattern of the considered simplified SBH model. The dashed (dashdotted) arrow represents the decay emitting a charged lepton (neutrino). The solid (dotted) arrow represents the decay emitting a ( or $h$) boson. Light pink (darker blue) arrows represent the decay emitting a charged (neutral) particle.
• Figure 3: Diagrams for the targeted cascade signatures in the SBH model. Final states with three light-flavor charged leptons (electrons or muons) are considered in the analysis. The decays of $\widetilde{\chi}^{0}_{2}$ and $\widetilde{\chi}^{\pm}_{1}$ are ignored as they only result in low-momentum particles that are almost never reconstructed.
• Figure 4: Distribution of $m_{3\ell}$ for the SM backgrounds and several signal hypotheses, normalized to unity. All SM backgrounds are included and no uncertainties are shown. A preselection is applied requesting exactly three baseline and signal leptons, and of at least one SFOS lepton pair.
• Figure 5: Relative fractions of signal production modes populating the SR channels. A signal with $m(\tilde{\ell}_{\mathrm{L}}\xspace, \widetilde{\chi}^{0}_{3}\xspace, \widetilde{\chi}^{0}_{1}\xspace)=(300, 200, 100)~\text{Ge V}\xspace$ is shown as an example. Mass-degenerate $\tilde{e}_{\mathrm{L}}$, $\tilde{\mu}_{\mathrm{L}}$ and $\tilde{\nu}$ is considered. The $m_{3\ell}$ bins are merged and $\texttt{SRSS}$-$2\mu$ is divided into $\texttt{SRSS}$-$e\mu\mu$ and $\texttt{SRSS}$-$\mu\mu\mu$ for illustration.