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LHC, CERN

CMS-EXO-19-002 ; CERN-EP-2019-237
Search for physics beyond the standard model in multilepton final states in proton-proton collisions at $\sqrt{s} = $ 13 TeV
JHEP 03 (2020) 051
Abstract: A search for physics beyond the standard model in events with at least three charged leptons (electrons or muons) is presented. The data sample corresponds to an integrated luminosity of 137 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = $ 13 TeV, collected with the CMS detector at the LHC in 2016-2018. The two targeted signal processes are pair production of type-III seesaw heavy fermions and production of a light scalar or pseudoscalar boson in association with a pair of top quarks. The heavy fermions may be manifested as an excess of events with large values of leptonic transverse momenta or missing transverse momentum. The light scalars or pseudoscalars may create a localized excess in the dilepton mass spectra. The results exclude heavy fermions of the type-III seesaw model for masses below 880 GeV at 95% confidence level in the scenario of equal branching fractions to each lepton flavor. This is the most restrictive limit on the flavor-democratic scenario of the type-III seesaw model to date. Assuming a Yukawa coupling of unit strength to top quarks, branching fractions of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) and 0.04 (0.03) are excluded at 95% confidence level for masses in the range 15-75 and 108-340 GeV, respectively. These are the first limits in these channels on an extension of the standard model with scalar or pseudoscalar particles.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Leading order Feynman diagrams for the type-III seesaw (left) and $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ (right) signal models, depicting example production and decay modes in pp collisions.

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Figure 1-a:
Leading order Feynman diagram for the type-III seesaw signal model, depicting example production and decay modes in pp collisions.

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Figure 1-b:
Leading order Feynman diagram for the $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal model, depicting example production and decay modes in pp collisions.

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Figure 2:
The $ {M_{\mathrm {T}}}$ distribution in the WZ-enriched control region (upper left), the $ {L_{\mathrm {T}}}$ distribution in the ${\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z} $-enriched control region (upper right), the $ {S_{\mathrm {T}}}$ distribution in the $\mathrm{Z} \mathrm{Z} $-enriched control region (lower left), and the $ {L_{\mathrm {T}}}$ distribution in the misidentified-lepton (Z+jets) enriched control region (lower right). The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins contain the overflow events in each distribution.

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Figure 2-a:
The $ {M_{\mathrm {T}}}$ distribution in the WZ-enriched control region. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 2-b:
The $ {L_{\mathrm {T}}}$ distribution in the ${\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z} $-enriched control region. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 2-c:
The $ {S_{\mathrm {T}}}$ distribution in the $\mathrm{Z} \mathrm{Z} $-enriched control region. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 2-d:
The $ {L_{\mathrm {T}}}$ distribution in the misidentified-lepton (Z+jets) enriched control region. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 3:
Type-III seesaw signal regions in 3L below-Z (upper left), on-Z (upper right), above-Z (lower left), and OSSF0 (lower right) events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins contain the overflow events in each distribution.

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Figure 3-a:
Type-III seesaw signal region in 3L below-Z events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 3-b:
Type-III seesaw signal region in 3L on-Z events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 3-c:
Type-III seesaw signal region in 3L above-Z events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 3-d:
Type-III seesaw signal region in 3L OSSF0 events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in the distribution.

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Figure 4:
Type-III seesaw signal regions in 4L OSSF0 (upper left), OSSF1 (upper right), and OSSF2 (lower) events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins contain the overflow events in each distribution.

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Figure 4-a:
Type-III seesaw signal region in 4L OSSF0 events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in each distribution.

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Figure 4-b:
Type-III seesaw signal region in 4L OSSF1 events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in each distribution.

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Figure 4-c:
Type-III seesaw signal region in 4L OSSF2 events. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for type-III seesaw models with $\Sigma $ masses of 300 and 700 GeV in the flavor-democratic scenario are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represent only the statistical uncertainty of the backgrounds. The rightmost bin contains the overflow events in each distribution.

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Figure 5:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ (left column) and $ {M_{\mathrm {OSSF}}}^{300}$ (right column) distributions in the 3L(ee) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. Upper, center, and lower plots are for $ {S_{\mathrm {T}}} < $ 400 GeV, 400 $ < {S_{\mathrm {T}}} < $ 800 GeV, and $ {S_{\mathrm {T}}} > $ 800 GeV, respectively. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins do not contain the overflow events as these are outside the probed mass ranges.

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Figure 5-a:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L(ee) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 5-b:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L(ee) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 5-c:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L(ee) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 5-d:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L(ee) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 5-e:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L(ee) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 5-f:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L(ee) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 6:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ (left column) and $ {M_{\mathrm {OSSF}}}^{300}$ (right column) distributions in the 3L(ee) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. Upper, center, and lower plots are for $ {S_{\mathrm {T}}} < $ 400 GeV, 400 $ < {S_{\mathrm {T}}} < $ 800 GeV, and $ {S_{\mathrm {T}}} > $ 800 GeV, respectively. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins do not contain the overflow events as these are outside the probed mass ranges.

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Figure 6-a:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L(ee) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel representd only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 6-b:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L(ee) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel representd only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 6-c:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L(ee) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel representd only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 6-d:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L(ee) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel representd only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 6-e:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L(ee) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel representd only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 6-f:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L(ee) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel representd only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 7:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ (left column) and $ {M_{\mathrm {OSSF}}}^{300}$ (right column) distributions in the 4L(ee) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. Upper, center, and lower plots are for 0B $ {S_{\mathrm {T}}} < $ 400 GeV, 0B $ {S_{\mathrm {T}}} > $ 400 GeV, and 1B $ {S_{\mathrm {T}}}$-inclusive, respectively. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins do not contain the overflow events as these are outside the probed mass range.

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Figure 7-a:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 4L(ee) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plots is for 0B $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin doed not contain the overflow events as these are outside the probed mass range.

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Figure 7-b:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 4L(ee) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plots is for 0B $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin doed not contain the overflow events as these are outside the probed mass range.

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Figure 7-c:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 4L(ee) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plots is for 0B $ {S_{\mathrm {T}}} > $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin doed not contain the overflow events as these are outside the probed mass range.

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Figure 7-d:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 4L(ee) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plots is for 0B $ {S_{\mathrm {T}}} > $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin doed not contain the overflow events as these are outside the probed mass range.

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Figure 7-e:
Dielectron $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 4L(ee) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plots is for 1B $ {S_{\mathrm {T}}}$-inclusive. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin doed not contain the overflow events as these are outside the probed mass range.

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Figure 7-f:
Dielectron $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 4L(ee) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plots is for 1B $ {S_{\mathrm {T}}}$-inclusive. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to {\mathrm{e} \mathrm{e}}$) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mathrm{e} \mathrm{e})=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin doed not contain the overflow events as these are outside the probed mass range.

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Figure 8:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ (left column) and $ {M_{\mathrm {OSSF}}}^{300}$ (right column) distributions in the 3L($\mu \mu $) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. Upper, center, and lower plots are for $ {S_{\mathrm {T}}} < $ 400 GeV, 400 $ < {S_{\mathrm {T}}} < $ 800 GeV, and $ {S_{\mathrm {T}}} > $ 800 GeV, respectively. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins do not contain the overflow events as these are outside the probed mass range.

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Figure 8-a:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L($\mu \mu $) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray bands in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 8-b:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L($\mu \mu $) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray bands in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 8-c:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L($\mu \mu $) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray bands in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 8-d:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L($\mu \mu $) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray bands in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 8-e:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L($\mu \mu $) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray bands in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 8-f:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L($\mu \mu $) 0B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray bands in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 9:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ (left column) and $ {M_{\mathrm {OSSF}}}^{300}$ (right column) distributions in the 3L($\mu \mu $) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. Upper, center, and lower plots are for $ {S_{\mathrm {T}}} < $ 400 GeV, 400 $ < {S_{\mathrm {T}}} < $ 800 GeV, and $ {S_{\mathrm {T}}} > $ 800 GeV, respectively. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins do not contain the overflow events as these are outside the probed mass range.

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Figure 9-a:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L($\mu \mu $) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray bands in the upper panel and the light gray band in the lower panel represents the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 9-b:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L($\mu \mu $) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray bands in the upper panel and the light gray band in the lower panel represents the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 9-c:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L($\mu \mu $) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray bands in the upper panel and the light gray band in the lower panel represents the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 9-d:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L($\mu \mu $) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 400 $ < {S_{\mathrm {T}}} < $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray bands in the upper panel and the light gray band in the lower panel represents the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 9-e:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 3L($\mu \mu $) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray bands in the upper panel and the light gray band in the lower panel represents the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 9-f:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 3L($\mu \mu $) 1B $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for $ {S_{\mathrm {T}}} > $ 800 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray bands in the upper panel and the light gray band in the lower panel represents the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 10:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ (left column) and $ {M_{\mathrm {OSSF}}}^{300}$ (right column) distributions in the 4L($\mu \mu $) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. Upper, center, and lower plots are for 0B $ {S_{\mathrm {T}}} < $ 400 GeV, 0B $ {S_{\mathrm {T}}} > $ 400 GeV, and 1B $ {S_{\mathrm {T}}}$-inclusive, respectively. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panels show the ratio of observed to expected events. The hatched gray bands in the upper panels and the light gray bands in the lower panels represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray bands in the lower panels represent only the statistical uncertainty of the backgrounds. The rightmost bins do not contain the overflow events as these are outside the probed mass range.

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Figure 10-a:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 4L($\mu \mu $) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 0B $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 10-b:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 4L($\mu \mu $) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 0B $ {S_{\mathrm {T}}} < $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 10-c:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 4L($\mu \mu $) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 0B $ {S_{\mathrm {T}}} > $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 10-d:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 4L($\mu \mu $) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 0B $ {S_{\mathrm {T}}} > $ 400 GeV. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 10-e:
Dimuon $ {M_{\mathrm {OSSF}}}^{20}$ distribution in the 4L($\mu \mu $) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 1B $ {S_{\mathrm {T}}}$-inclusive. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 10-f:
Dimuon $ {M_{\mathrm {OSSF}}}^{300}$ distribution in the 4L($\mu \mu $) $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal regions. The plot is for 1B $ {S_{\mathrm {T}}}$-inclusive. The total SM background is shown as a stacked histogram of all contributing processes. The predictions for $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}(\to \mu \mu $) models with a pseudoscalar (scalar) $\phi $ of 20 and 125 (70 and 300) GeV mass assuming $g_{\mathrm{t}}^2\mathcal {B}(\phi \to \mu \mu)=$ 0.05 are also shown. The lower panel shows the ratio of observed to expected events. The hatched gray band in the upper panel and the light gray band in the lower panel represent the total (systematic and statistical) uncertainty of the backgrounds in each bin, whereas the dark gray band in the lower panel represents only the statistical uncertainty of the backgrounds. The rightmost bin does not contain the overflow events as these are outside the probed mass range.

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Figure 11:
The 95% confidence level expected and observed upper limits on the total production cross section of heavy fermion pairs. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. Also shown are the theoretical prediction for the cross section and the associated uncertainty of the $\Sigma $ pair production via the type-III seesaw mechanism. Type-III seesaw heavy fermions are excluded for masses below 880 GeV (expected limit 930 GeV) in the flavor-democratic scenario.

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Figure 12:
The 95% confidence level expected and observed upper limits on the product of the signal production cross section and branching fraction of a scalar $\phi $ boson in the dielectron (upper left) and dimuon (lower left) channels, and of a pseudoscalar $\phi $ boson in the dielectron (upper right) and dimuon (lower right) channels, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. Also shown are the theoretical predictions for the product of the production cross section and branching fraction of the $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ model, with their uncertainties, and assuming ${g}_{t}^2\mathcal {B}(\phi \to {\mathrm{e} \mathrm{e}}/\mu \mu)=$ 0.05. All $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal scenarios are excluded for production cross sections above 20 fb for $\phi $ masses in the range of 15-75 GeV, and above 5 fb for $\phi $ masses in the range of 108-340 GeV.

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Figure 12-a:
The 95% confidence level expected and observed upper limits on the product of the signal production cross section and branching fraction of a scalar $\phi $ boson in the dielectron channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. Also shown are the theoretical predictions for the product of the production cross section and branching fraction of the $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ model, with their uncertainties, and assuming ${g}_{t}^2\mathcal {B}(\phi \to {\mathrm{e} \mathrm{e}}/\mu \mu)=$ 0.05. All $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal scenarios are excluded for production cross sections above 20 fb for $\phi $ masses in the range of 15-75 GeV, and above 5 fb for $\phi $ masses in the range of 108-340 GeV.

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Figure 12-b:
The 95% confidence level expected and observed upper limits on the product of the signal production cross section and branching fraction of a scalar $\phi $ boson in the dimuon channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. Also shown are the theoretical predictions for the product of the production cross section and branching fraction of the $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ model, with their uncertainties, and assuming ${g}_{t}^2\mathcal {B}(\phi \to {\mathrm{e} \mathrm{e}}/\mu \mu)=$ 0.05. All $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal scenarios are excluded for production cross sections above 20 fb for $\phi $ masses in the range of 15-75 GeV, and above 5 fb for $\phi $ masses in the range of 108-340 GeV.

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Figure 12-c:
The 95% confidence level expected and observed upper limits on the product of the signal production cross section and branching fraction of a pseudoscalar $\phi $ boson in the dielectron channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. Also shown are the theoretical predictions for the product of the production cross section and branching fraction of the $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ model, with their uncertainties, and assuming ${g}_{t}^2\mathcal {B}(\phi \to {\mathrm{e} \mathrm{e}}/\mu \mu)=$ 0.05. All $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal scenarios are excluded for production cross sections above 20 fb for $\phi $ masses in the range of 15-75 GeV, and above 5 fb for $\phi $ masses in the range of 108-340 GeV.

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Figure 12-d:
The 95% confidence level expected and observed upper limits on the product of the signal production cross section and branching fraction of a pseudoscalar $\phi $ boson in the dimuon channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. Also shown are the theoretical predictions for the product of the production cross section and branching fraction of the $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ model, with their uncertainties, and assuming ${g}_{t}^2\mathcal {B}(\phi \to {\mathrm{e} \mathrm{e}}/\mu \mu)=$ 0.05. All $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal scenarios are excluded for production cross sections above 20 fb for $\phi $ masses in the range of 15-75 GeV, and above 5 fb for $\phi $ masses in the range of 108-340 GeV.

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Figure 13:
The 95% confidence level expected and observed upper limits on the product of the square of the Yukawa coupling to top quarks and branching fraction of a scalar $\phi $ boson in the dielectron (upper left) and dimuon (lower left) channels, and of a pseudoscalar $\phi $ boson in the dielectron (upper right) and dimuon (lower right) channels, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. The dashed horizontal line marks the unity value of the product of the square of the Yukawa coupling to top quarks and the branching fraction. Assuming a Yukawa coupling of unit strength to top quarks, the branching fraction of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) are excluded for masses in the range of 15-75 GeV, and above 0.04 (0.03) for masses in the range of 108-340 GeV.

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Figure 13-a:
The 95% confidence level expected and observed upper limits on the product of the square of the Yukawa coupling to top quarks and branching fraction of a scalar $\phi $ boson in the dielectron channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. The dashed horizontal line marks the unity value of the product of the square of the Yukawa coupling to top quarks and the branching fraction. Assuming a Yukawa coupling of unit strength to top quarks, the branching fraction of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) are excluded for masses in the range of 15-75 GeV, and above 0.04 (0.03) for masses in the range of 108-340 GeV.

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Figure 13-b:
The 95% confidence level expected and observed upper limits on the product of the square of the Yukawa coupling to top quarks and branching fraction of a scalar $\phi $ boson in the dimuon channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. The dashed horizontal line marks the unity value of the product of the square of the Yukawa coupling to top quarks and the branching fraction. Assuming a Yukawa coupling of unit strength to top quarks, the branching fraction of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) are excluded for masses in the range of 15-75 GeV, and above 0.04 (0.03) for masses in the range of 108-340 GeV.

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Figure 13-c:
The 95% confidence level expected and observed upper limits on the product of the square of the Yukawa coupling to top quarks and branching fraction of a pseudoscalar $\phi $ boson in the dielectron channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. The dashed horizontal line marks the unity value of the product of the square of the Yukawa coupling to top quarks and the branching fraction. Assuming a Yukawa coupling of unit strength to top quarks, the branching fraction of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) are excluded for masses in the range of 15-75 GeV, and above 0.04 (0.03) for masses in the range of 108-340 GeV.

png pdf
Figure 13-d:
The 95% confidence level expected and observed upper limits on the product of the square of the Yukawa coupling to top quarks and branching fraction of a pseudoscalar $\phi $ boson in the dimuon channel, where $\phi $ is produced in association with a top quark pair. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The vertical hatched gray band indicates the mass region corresponding to the Z boson veto. The dashed horizontal line marks the unity value of the product of the square of the Yukawa coupling to top quarks and the branching fraction. Assuming a Yukawa coupling of unit strength to top quarks, the branching fraction of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) are excluded for masses in the range of 15-75 GeV, and above 0.04 (0.03) for masses in the range of 108-340 GeV.
Tables

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Table 1:
Multilepton signal region definitions for the type-III seesaw signal model. All events containing a same-flavor lepton pair with invariant mass below 12 GeV are removed in the 3L and 4L event categories. Furthermore, 3L events containing an OSSF lepton pair with mass below 76 GeV when the trilepton mass is within a Z boson mass window (91 $\pm$ 15 GeV) are also rejected. The last $ {L_{\mathrm {T}}}+ {{p_{\mathrm {T}}} ^\text {miss}}$ or $ {M_{\mathrm {T}}}$ bin in each signal region contains the overflow events.

png pdf
Table 2:
Multilepton signal region definitions for the $ {{\mathrm{t} {}\mathrm{\bar{t}}} \phi}$ signal model. All events containing a same-flavor lepton pair with invariant mass below 12 GeV are removed in the 3L and 4L event categories. Furthermore, 3L events containing an OSSF lepton pair with mass below 76 GeV when the trilepton mass is within a Z boson mass window (91 $\pm$ 15 GeV) are also rejected.

png pdf
Table 3:
Sources of systematic uncertainties, affected background and signal processes, relative variations of the affected processes, and presence or otherwise of correlation between years in signal regions.

png pdf
Table 4:
Product of the fiducial acceptance and the event selection efficiency for the signal models at various signal mass hypotheses calculated after all analysis selection requirements.
Summary
A search has been performed for physics beyond the standard model, using multilepton events in 137 fb$^{-1}$ of pp collision data at $\sqrt{s} = $ 13 TeV, collected with the CMS detector in 2016-2018. The observations are found to be consistent with the expectations from standard model processes, with no statistically significant signal-like excess in any of the probed channels. The results are used to constrain the allowed parameter space of the targeted signal models. At 95% confidence level, heavy fermions of the type-III seesaw model with masses below 880 GeV are excluded assuming identical $\Sigma$ decay branching fractions across all lepton flavors. This is the most restrictive limit on the flavor-democratic scenario of the type-III seesaw model to date. Assuming a Yukawa coupling of unit strength to top quarks, branching fractions of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) are excluded at 95% confidence level for masses in the range 15-75 GeV, and above 0.04 (0.03) for masses in the range 108-340 GeV. These are the first limits in these channels on an extension of the standard model with scalar or pseudoscalar particles.
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