Search for supersymmetry in events with four or more leptons in $\sqrt{s}=13\mathrm{TeV}$ $pp$ collisions with ATLAS

Results from a search for supersymmetry in events with four or more charged leptons (electrons, muons and taus) are presented. The analysis uses a data sample corresponding to $36.1{\mathrm{fb}}^{-1}$ of proton–proton collisions delivered by the Large Hadron Collider at $\sqrt{s}=13\mathrm{TeV}$ and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying taus are designed to target a range of supersymmetric scenarios that can be either enriched in or depleted of events involving the production and decay of a $Z$ boson. Data yields are consistent with Standard Model expectations and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge mediated supersymmetry, where Higgsino masses are excluded up to 295 GeV. In $R$-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.46, 1.06, and 2.25 TeV are placed on wino, slepton and gluino masses, respectively.

Figure 1

Diagrams of the benchmark SUSY models of RPC NLSP pair production of (a) and (b) a wino, (c) slepton/sneutrino and (d) gluino, followed by the RPV decay of the ${\tilde{\chi }}_1^0$ LSP. The LSP is assumed to decay as ${\tilde{\chi }}_1^0\to \ell \ell \nu$ with 100% branching ratio.

Figure 2

Diagrams of the processes in the SUSY RPC GGM Higgsino models. The $W^{*}/Z^{*}$ produced in the ${\tilde{\chi }}_1^{\pm }/{\tilde{\chi }}_2^0$ decays are off-shell ($m\sim 1\mathrm{GeV}$) and their decay products are usually not reconstructed.

Figure 3

Breakdown of the dominant systematic uncertainties in the background estimates for the signal regions. The individual uncertainties can be correlated, and do not necessarily sum in quadrature to the total background uncertainty. The text provides category details.

Figure 4

The distributions for data and the estimated SM backgrounds in VR0 and VR0Z for (a) and (c) the electron and muon $p_{\mathrm{T}}$, (b) the SFOS invariant mass, and (d) the $E_{\mathrm{T}}^{\mathrm{miss}}$. “Other” is the sum of the $tWZ$, $t\overline{t}WW$, and $t\overline{t}t\overline{t}$ backgrounds. The last bin includes the overflow. Both the statistical and systematic uncertainties in the SM background are included in the shaded band.

Figure 5

The distributions for data and the estimated SM backgrounds in VR1 and VR2 for (a) and (c) the light lepton $p_{\mathrm{T}}$, and (b) and (d) the tau $p_{\mathrm{T}}$. “Other” is the sum of the $tWZ$, $t\overline{t}WW$, and $t\overline{t}t\overline{t}$ backgrounds. The last bin includes the overflow. Both the statistical and systematic uncertainties in the SM background are included in the shaded band.

Figure 6

The (a), (c) and (d) $m_{\mathrm{eff}}$ distribution for events passing the signal region requirements except the $m_{\mathrm{eff}}$ requirement in SR0A, SR0B, SR1 and SR2. The (b)$E_{\mathrm{T}}^{\mathrm{miss}}$ distribution is shown for events passing the signal region requirements except the $E_{\mathrm{T}}^{\mathrm{miss}}$ requirement in SR0C and SR0D. Distributions for data, the estimated SM backgrounds, and an example SUSY scenario are shown. “Other” is the sum of the $tWZ$, $t\overline{t}WW$, and $t\overline{t}t\overline{t}$ backgrounds. The last bin captures the overflow events. Both the statistical and systematic uncertainties in the SM background are included in the shaded band. The red arrows indicate the $m_{\mathrm{eff}}$ or $E_{\mathrm{T}}^{\mathrm{miss}}$ selections in the signal regions.

Figure 7

Expected (dashed) and observed (solid) 95% C.L. exclusion limits on (a) wino $W/Z$ NLSP, and (b) wino $W/h$ NLSP pair production with RPV ${\tilde{\chi }}_1^0$ decays via ${\lambda }_{12k}$, or ${\lambda }_{i33}$ where $i$, $k\in 1$, 2. The limits are set using the statistical combination of disjoint signal regions. Where the signal regions are not mutually exclusive, the observed ${\mathrm{CL}}_{\mathrm{s}}$ value is taken from the signal region with the better expected ${\mathrm{CL}}_{\mathrm{s}}$ value.

Figure 8

Expected (dashed) and observed (solid) 95% C.L. exclusion limits on (a) ${\tilde{\ell }}_{\mathrm{L}}/\tilde{\nu }$ NLSP, and (b) gluino NLSP pair production with RPV ${\tilde{\chi }}_1^0$ decays via ${\lambda }_{12k}$, or ${\lambda }_{i33}$ where $i$, $k\in 1$, 2. The limits are set using the statistical combination of disjoint signal regions. Where the signal regions are not mutually exclusive, the observed ${\mathrm{CL}}_{\mathrm{s}}$ value is taken from the signal region with the better expected ${\mathrm{CL}}_{\mathrm{s}}$ value.

Figure 9

Expected (dashed) and observed (solid) 95% C.L. exclusion limits on the Higgsino GGM models. The limits are set using the statistical combination of disjoint signal regions. Where the signal regions are not mutually exclusive, the observed ${\mathrm{CL}}_{\mathrm{s}}$ value is taken from the signal region with the better expected ${\mathrm{CL}}_{\mathrm{s}}$ value.