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Search for direct top squark pair production in events with a Higgs or $Z$ boson, and missing transverse momentum in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

The collaboration
No Journal Information, 2017

Abstract (data abstract)
A search for direct top squark pair production resulting in events with either a same-flavour opposite-sign dilepton pair with invariant mass compatible with a $Z$ boson or a pair of jets compatible with a Standard Model (SM) Higgs boson ($h$) is presented. Requirements on additional leptons, jets, jets identified as originating from b-quarks, and missing transverse momentum are imposed to target the other decay products of the top squark pair. The analysis is performed using proton-proton collision data at sqrt{s} = 13 TeV collected with the ATLAS detector at the LHC in 2015-2016, corresponding to an integrated luminosity of 36.1 fb$^{−1}$. No excess is observed in the data with respect to the expected SM predictions. The results are interpreted in two sets of models. In the first set, direct production of pairs of lighter top squarks ($\tilde{t}_1$) with long decay chains involving $Z$ or Higgs bosons is considered. The second set includes direct pair production of the heavier top squark pairs ($\tilde{t}_2$) decaying via $\tilde{t}_2 \rightarrow Z \tilde{t}_1$ or $\tilde{t}_2 \rightarrow h \tilde{t}_1$. The results exclude at 95% confidence level $\tilde{t}_2$ and $\tilde{t}_1$ masses up to about 800 GeV, extending the exclusion region of supersymmetric parameter space covered by previous LHC searches.

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Tabulated data from the publication's Figure 2a

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Jet multiplicity distributions in control regions CR$^{3\ell 1b}_{t\bar{t}Z}$, after normalising the $t\bar{t}Z$ and multi-boson background processes via the simultaneous fit...

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Tabulated data from the publication's Figure 2b

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Jet multiplicity distributions in control region CR$^{3\ell 1b}_{VV}$, after normalising the $t\bar{t}Z$ and multi-boson background processes via the simultaneous fit...

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Tabulated data from the publication's Figure 3a

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Jet multiplicity distributions in control regions CR$^{1\ell 4b}_{t\bar{t},A}$, after normalising the $t\bar{t}$ background process via the simultaneous fit described in...

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Tabulated data from the publication's Figure 3b

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Jet multiplicity distributions in control regions CR$^{1\ell 4b}_{t\bar{t},B}$, after normalising the $t\bar{t}$ background process via the simultaneous fit described in...

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Tabulated data from the publication's Figure 3c

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Jet multiplicity distributions in control regions CR$^{1\ell 4b}_{t\bar{t},C}$, after normalising the $t\bar{t}$ background process via the simultaneous fit described in...

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Tabulated data from the publication's Figure 4a

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Distribution of $E^{T}_\text{miss}$ for events passing all the signal candidate selection requirements, except that on $E^{T}_\text{miss}$, for SR$^{3\ell 1b}_A$ after...

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Tabulated data from the publication's Figure 4c

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Distribution of $E^{T}_\text{miss}$ for events passing all the signal candidate selection requirements, except that on $E^{T}_\text{miss}$, for SR$^{3\ell 1b}_B$ after...

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Tabulated data from the publication's Figure 4e

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Distribution of $E^{T}_\text{miss}$ for events passing all the signal candidate selection requirements, except that on $E^{T}_\text{miss}$, for SR$^{3\ell 1b}_C$ after...

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Tabulated data from the publication's Figure 4b

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Distribution of $E^{T}_\text{miss}$ for events passing all the signal candidate selection requirements, except that on $E^{T}_\text{miss}$, for SR$^{1\ell 4b}_A$ after...

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Tabulated data from the publication's Figure 4d

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Distribution of $E^{T}_\text{miss}$ for events passing all the signal candidate selection requirements, except that on $E^{T}_\text{miss}$, for SR$^{1\ell 4b}_B$ after...

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Tabulated data from the publication's Figure 4f

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Distribution of $E^{T}_\text{miss}$ for events passing all the signal candidate selection requirements, except that on $E^{T}_\text{miss}$, for SR$^{1\ell 4b}_C$ after...

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Tabulated data from the publication's Figure 5 expected limits

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Expected exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

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Tabulated data from the publication's Figure 5 observed limits

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Observed exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

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Tabulated data from the publication's Figure 6a observed limits

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Observed exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

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Tabulated data from the publication's Figure 6a expected limits

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Expected exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

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Tabulated data from the publication's Figure 6b observed limits

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Observed exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

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Tabulated data from the publication's Figure 6b expected limits

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Expected exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### 3l1b Obs limit MSTOP2 = 600 GeV MN01 = 250 GeV

Tabulated data from the publication's Figure 7 left observed limits

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Observed exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### 3l1b Exp limit MSTOP2 = 600 GeV MN01 = 250 GeV

Tabulated data from the publication's Figure 7 left expected limits

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Expected exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### 1l4b Exp limit MSTOP2 = 600 GeV MN01 = 250 GeV

Tabulated data from the publication's Figure 7 left expected limits

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Expected exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### 3l1b Obs limit MSTOP2 = 650 GeV MN01 = 200 GeV

Tabulated data from the publication's Figure 7 right observed limits

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Observed exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### 3l1b Exp limit MSTOP2 = 650 GeV MN01 = 200 GeV

Tabulated data from the publication's Figure 7 right expected limits

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Expected exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### 1l4b Obs limit MSTOP2 = 650 GeV MN01 = 200 GeV

Tabulated data from the publication's Figure 7 right observed limits

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Observed exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### 1l4b Exp limit MSTOP2 = 650 GeV MN01 = 200 GeV

Tabulated data from the publication's Figure 7 right expected limits

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Expected exclusion limits at 95% CL from the analysis of $36.1 \; \text{fb}^{-1}$ of 13 TeV $pp$ collision data as...

• #### Table 7

Tabulated data from the publication's Table 7

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Background fit results for the control and validation regions in the 1$\ell$4$b$ selection. The nominal predictions from MC simulation are...

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Tabulated data from the publication's Table 8

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Summary of the main systematic uncertainties and their impact (in %) on the total SM background prediction in each of...

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Tabulated data from the publication's Table 9 Up

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Observed and expected numbers of events the three 3$\ell$1$b$ Signal regions. The nominal predictions from MC simulation are given for...

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Tabulated data from the publication's Table 9 Down

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Observed and expected numbers of events in the three 1$\ell$4$b$ signal regions. The nominal predictions from MC simulation are given...

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Tabulated data from the publication's auxiliary material Figure 1a

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Illustration of the best expected signal region per signal grid point for the $\tilde{t}_2 \rightarrow h\tilde{t}_1$ models with $\tilde{t}_1\to t\tilde{\chi}^0_1$....

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Tabulated data from the publication's auxiliary material Figure 1b

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Illustration of the best expected signal region per signal grid point for the $\tilde{t}_2 \rightarrow Z\tilde{t}_1$ models with $\tilde{t}_1\to t\tilde{\chi}^0_1$....

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Tabulated data from the publication's auxiliary material Figure 2a

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Jet multiplicity distributions in VR$^{1\ell 4b}_C$ for an integrated luminosity of 36.1 fb$^{-1}$. The contributions from all SM backgrounds are...

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Tabulated data from the publication's auxiliary material Figure 2b

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Jet multiplicity distributions in VR$^{1\ell 4b}_B$ for an integrated luminosity of 36.1 fb$^{-1}$. The contributions from all SM backgrounds are...

• #### Aux : Figure 2c

Tabulated data from the publication's auxiliary material Figure 2c

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Jet multiplicity distributions in VR$^{1\ell 4b}_A$ for an integrated luminosity of 36.1 fb$^{-1}$. The contributions from all SM backgrounds are...

• #### Aux : Figure 3a

Tabulated data from the publication's auxiliary material Figure 3a

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E$^{T}_\text{miss}$ distributions in VR$^{1\ell 4b}_C$ for an integrated luminosity of 36.1 fb$^{-1}$. The contributions from all SM backgrounds are shown...

• #### Aux : Figure 3b

Tabulated data from the publication's auxiliary material Figure 3b

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E$^{T}_\text{miss}$ distributions in VR$^{1\ell 4b}_B$ for an integrated luminosity of 36.1 fb$^{-1}$. The contributions from all SM backgrounds are shown...

• #### Aux : Figure 3c

Tabulated data from the publication's auxiliary material Figure 3c

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$E^{T}_\text{miss}$ distributions in VR$^{1\ell 4b}_A$ for an integrated luminosity of 36.1 fb$^{-1}$. The contributions from all SM backgrounds are shown...

• #### Aux : Figure 4a

Tabulated data from the publication's auxiliary material Figure 4a

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Jet multiplicity for events with at least 3 jets, one $b$-tagged jets for an integrated luminosity of 36.1 fb$^{-1}$. The...

• #### Aux : Figure 4b

Tabulated data from the publication's auxiliary material Figure 4b

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$E^{T}_\text{miss}$ for events with at least 3 jets, one $b$-tagged jets for an integrated luminosity of 36.1 fb$^{-1}$. The contributions...

• #### Aux : Figure 4c

Tabulated data from the publication's auxiliary material Figure 4c

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$p_{\rm T}^{\ell\ell}$ for events with at least 3 jets, one $b$-tagged jets for an integrated luminosity of 36.1 fb$^{-1}$. The...

• #### Aux : Figure 5

Tabulated data from the publication's auxiliary material Figure 5

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Distribution of $m_{bb}$ for events passing all the signal selection requirements, except that on $m_{bb}$, for SR$^{1\ell 4b}_A$ after the...

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Tabulated data from the publication's auxiliary material Figure 6

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• #### Aux : Figure 6c

Tabulated data from the publication's auxiliary material Figure 6c

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Upper limits on cross-sections (in fb) at 95% CL for $\tilde{t}_2$ pair production with $\tilde{t}_2 \to \tilde{t}_1 Z$ with $\tilde{t}_1... • #### Aux : Figure 7a Tabulated data from the publication's auxiliary material Figure 7a 10.17182/hepdata.77997.v2/t44 SR$^{3\ell 1b}_A$acceptance for each signal model. • #### Aux : Figure 7b Tabulated data from the publication's auxiliary material Figure 7b 10.17182/hepdata.77997.v2/t45 SR$^{3\ell 1b}_B$acceptance for each signal model. • #### Aux : Figure 7c Tabulated data from the publication's auxiliary material Figure 7c 10.17182/hepdata.77997.v2/t46 SR$^{3\ell 1b}_C$acceptance for each signal model. • #### Aux : Figure 8a Tabulated data from the publication's auxiliary material Figure 8a 10.17182/hepdata.77997.v2/t47 SR$^{1\ell 4b}_A$acceptance for each signal model • #### Aux : Figure 8b Tabulated data from the publication's auxiliary material Figure 8b 10.17182/hepdata.77997.v2/t48 SR$^{1\ell 4b}_B$acceptance for each signal model • #### Aux : Figure 8c Tabulated data from the publication's auxiliary material Figure 8c 10.17182/hepdata.77997.v2/t49 SR$^{1\ell 4b}_C$acceptance for each signal model • #### Aux : Figure 9a Tabulated data from the publication's auxiliary material Figure 9a 10.17182/hepdata.77997.v2/t50 SR$^{3\ell 1b}_A$efficiency for each signal model • #### Aux : Figure 9b Tabulated data from the publication's auxiliary material Figure 9b 10.17182/hepdata.77997.v2/t51 SR$^{3\ell 1b}_B$efficiency for each signal model • #### Aux : Figure 9c Tabulated data from the publication's auxiliary material Figure 9c 10.17182/hepdata.77997.v2/t52 SR$^{3\ell 1b}_C$efficiency for each signal model • #### Aux : Figure 10a Tabulated data from the publication's auxiliary material Figure 10a 10.17182/hepdata.77997.v2/t53 SR$^{1\ell 4b}_A$efficiency for each signal model • #### Aux : Figure 10b Tabulated data from the publication's auxiliary material Figure 10b 10.17182/hepdata.77997.v2/t54 SR$^{1\ell 4b}_B$efficiency for each signal model • #### Aux : Figure 10c Tabulated data from the publication's auxiliary material Figure 10c 10.17182/hepdata.77997.v2/t55 SR$^{1\ell 4b}_C$efficiency for each signal model • #### Aux : Table 1 Tabulated data from the publication's auxiliary material Table 1 10.17182/hepdata.77997.v2/t56 Number of signal events selected at different stages for some scenarios in the$\tilde{t}_2 \rightarrow h\tilde{t}_1$with$\tilde{t}_1\to t\tilde{\chi}^0_1$model. • #### Aux : Table 2 Tabulated data from the publication's auxiliary material Table 2 10.17182/hepdata.77997.v2/t57 Number of signal events selected at different stages for some scenarios in the$\tilde{t}_2 \rightarrow Z\tilde{t}_1$with$\tilde{t}_1\to t\tilde{\chi}^0_1\$ model.

Version 2 modifications: Images for figures 3a and 3c had been swapped in the initial revision, this is now corrected.