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| CMS-PAS-SUS-17-004 | ||
| Combined search for electroweak production of charginos and neutralinos in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| August 2017 | ||
| Abstract: A statistical combination of several searches for the electroweak production of charginos and neutralinos is presented. All searches use 35.9 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}= $ 13 TeV recorded by CMS in 2016. In addition to previously performed searches, an optimized analysis requiring three or more charged leptons (electrons or muons) is presented, targeting the challenging scenario where the difference in mass between the two least massive neutralinos is approximately equal to the mass of the Z boson. The results are interpreted in simplified models of supersymmetric chargino-neutralino or neutralino pair production. When the lightest neutralino is massless in the chargino-neutralino model, the combined result obtains an observed (expected) limit at the 95% confidence level in the chargino mass of up to 650 (570) GeV in the most favorable scenario, improving upon the exclusion limits from individual analyses by up to 40 GeV. If the mass difference between the two least massive neutralinos is approximately equal to the mass of the Z boson in the chargino-neutralino model, the optimized search for three or more leptons obtains observed and expected exclusion limits of around 225 GeV in the second neutralino mass and 125 GeV in the lightest neutalino mass, improving the observed limit by as much as 60 GeV compared to the previously published result. In the neutralino pair production model, the observed (expected) exclusion limits from the combined result extends up to 650-750 (550-750) GeV depending on the branching fraction assumed, extending the observed exclusion achieved by individual analyses by up to 200 GeV. The combined result additionally excludes some intermediate gaps in the mass coverage of individual analyses. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 03 (2018) 160. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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Additional information on efficiencies needed for reinterpretation of these results are available here. Additional technical material for CMS speakers can be found here |
| Figures | |
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Figure 1:
Chargino-neutralino pair production with the chargino decaying to the W boson and the LSP and the neutralino decaying to either (left) a Z boson and the LSP or (right) a H boson and the LSP. |
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Figure 1-a:
Chargino-neutralino pair production with the chargino decaying to the W boson and the LSP and the neutralino decaying to a Z boson and the LSP. |
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Figure 1-b:
Chargino-neutralino pair production with the chargino decaying to the W boson and the LSP and the neutralino decaying to a H boson and the LSP. |
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Figure 2:
A GMSB model with neutralino-neutralino pair production and the neutralinos decaying into gravitinos and (left) two Z bosons, (center) a Z and a H boson, or (right) two H bosons. |
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Figure 2-a:
A GMSB model with neutralino-neutralino pair production and the neutralinos decaying into gravitinos and two Z bosons. |
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Figure 2-b:
A GMSB model with neutralino-neutralino pair production and the neutralinos decaying into gravitinos and a Z and a H boson. |
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Figure 2-c:
A GMSB model with neutralino-neutralino pair production and the neutralinos decaying into gravitinos and two H bosons. |
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Figure 3:
Cross section for $\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 $ production at $\sqrt {s} = $ 13 TeV versus the wino mass, assuming mass-degenerate wino $\tilde{\chi}^{\pm}_1$ and $ \tilde{\chi}^0_2 $. The various curves show different assumptions on the masses of the squarks and gluinos, as described in the legend. The green band shows the theoretical uncertainty in the cross section calculation for the 100 TeV squark and gluino mass assumption. |
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Figure 4:
Distributions of $ {{p_{\mathrm {T}}} ^\text {miss}} $ for two representative signal points in the WZ corridor as well as the expected SM background for $ {H_{\mathrm {T}}} < $ 100 (left) and $ > $ 200 GeV (right). For larger values of $ {H_{\mathrm {T}}} $ the shape difference between signal and background becomes more pronounced due to the presence of the LSPs. |
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Figure 4-a:
Distributions of $ {{p_{\mathrm {T}}} ^\text {miss}} $ for two representative signal points in the WZ corridor as well as the expected SM background for $ {H_{\mathrm {T}}} < $ 100 GeV. For larger values of $ {H_{\mathrm {T}}} $ the shape difference between signal and background becomes more pronounced due to the presence of the LSPs. |
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Figure 4-b:
Distributions of $ {{p_{\mathrm {T}}} ^\text {miss}} $ for two representative signal points in the WZ corridor as well as the expected SM background for $ {H_{\mathrm {T}}} > $ 200 GeV. For larger values of $ {H_{\mathrm {T}}} $ the shape difference between signal and background becomes more pronounced due to the presence of the LSPs. |
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Figure 5:
Distributions of the transverse mass of the third lepton (top left), the $ {{p_{\mathrm {T}}} ^\text {miss}} $ (top right), the $ {m_{\ell \ell}} $ of the OSSF pair (bottom left), and the $ {H_{\mathrm {T}}} $ (bottom right). Distributions for two signal mass points in the WZ corridor are overlaid for illustration. |
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Figure 5-a:
Distributions of the transverse mass of the third lepton. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. |
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Figure 5-b:
Distributions of the transverse mass of the $ {{p_{\mathrm {T}}} ^\text {miss}} $. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. |
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Figure 5-c:
Distributions of the transverse mass of the $ {m_{\ell \ell}} $ of the OSSF pair. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. |
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Figure 5-d:
Distributions of the transverse mass of the $ {H_{\mathrm {T}}} $. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. |
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Figure 6:
Expected and observed yield comparison in the search regions. Two example signal mass points along the WZ corridor are overlaid for illustration. |
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Figure 7:
The 95% CL upper limit on the production cross section in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the model of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with the WZ topology, using only the search requiring three or more leptons as described in Section 6. The thick solid black (dashed red) curve represents the observed (expected) exclusion contour assuming the theory cross sections. The area below each curve is the excluded region. The thin dashed red line indicates the $ \pm 1 \sigma _{\mathrm {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm 1 \sigma _{\mathrm {theory}}$) on the signal cross section. The $z$ axis shows the observed limit at 95% CL on the signal production cross section. |
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Figure 8:
The 95% CL upper limits on the production cross sections in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with (top) the WZ topology, (middle) the WH topology, or (bottom) the mixed topology with 50% branching fraction to each of WZ and WH. The thick solid black (dashed red) curve represents the observed (expected) exclusion contour assuming the theory cross sections. The area below each curve is the excluded region. The thin dashed red line indicates the $ \pm 1 \sigma _{\mathrm {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm 1 \sigma _{\mathrm {theory}}$) on the signal cross section. The $z$ axis shows the observed limit at 95% CL on the signal production cross section. |
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Figure 8-a:
The 95% CL upper limits on the production cross sections in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with the WZ topology. The thick solid black (dashed red) curve represents the observed (expected) exclusion contour assuming the theory cross sections. The area below each curve is the excluded region. The thin dashed red line indicates the $ \pm 1 \sigma _{\mathrm {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm 1 \sigma _{\mathrm {theory}}$) on the signal cross section. The $z$ axis shows the observed limit at 95% CL on the signal production cross section. |
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Figure 8-b:
The 95% CL upper limits on the production cross sections in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with the WH topology. The thick solid black (dashed red) curve represents the observed (expected) exclusion contour assuming the theory cross sections. The area below each curve is the excluded region. The thin dashed red line indicates the $ \pm 1 \sigma _{\mathrm {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm 1 \sigma _{\mathrm {theory}}$) on the signal cross section. The $z$ axis shows the observed limit at 95% CL on the signal production cross section. |
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Figure 8-c:
The 95% CL upper limits on the production cross sections in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with the mixed topology with 50% branching fraction to each of WZ and WH. The thick solid black (dashed red) curve represents the observed (expected) exclusion contour assuming the theory cross sections. The area below each curve is the excluded region. The thin dashed red line indicates the $ \pm 1 \sigma _{\mathrm {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm 1 \sigma _{\mathrm {theory}}$) on the signal cross section. The $z$ axis shows the observed limit at 95% CL on the signal production cross section. |
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Figure 9:
The analysis with the best expected exclusion limit at each point in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with (top) the WZ topology, (middle) the WH topology, or (bottom) the mixed topology 50% branching fraction to each of WZ and WH. |
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Figure 9-a:
The analysis with the best expected exclusion limit at each point in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with the WZ topology. |
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Figure 9-b:
The analysis with the best expected exclusion limit at each point in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with the WH topology. |
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Figure 9-c:
The analysis with the best expected exclusion limit at each point in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production with the mixed topology 50% branching fraction to each of WZ and WH. |
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Figure 10:
Exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production (left) for the individual analyses and (right) for the combination of analyses. The decay modes assumed for each contour are given in the legends. |
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Figure 10-a:
Exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production for the individual analyses. The decay modes assumed for each contour are given in the legends. |
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Figure 10-b:
Exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^{\pm}_1}} $ and $ {m_{\tilde{\chi}^0_1}} $ for the models of $ {\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 } $ production for the combination of analyses. The decay modes assumed for each contour are given in the legends. |
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Figure 11:
Combined exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^0_1}} $ and $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production. The area to the left of or below the solid (dashed) black curve represents the observed (expected) exclusion region. The green and yellow bands indicate the $\pm $1 and 2 standard deviation ($\sigma $) uncertainties in the expected limit. The thin black lines show the effect of the theoretical uncertainties ($ \pm $1$ \sigma _{\mathrm {theory}}$) on the signal cross section. |
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Figure 11-a:
Combined exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^0_1}} $ and $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production. The area to the left of or below the solid (dashed) black curve represents the observed (expected) exclusion region. The green and yellow bands indicate the $\pm $1 and 2 standard deviation ($\sigma $) uncertainties in the expected limit. The thin black lines show the effect of the theoretical uncertainties ($ \pm $1$ \sigma _{\mathrm {theory}}$) on the signal cross section. |
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Figure 11-b:
Combined exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^0_1}} $ and $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production. The area to the left of or below the solid (dashed) black curve represents the observed (expected) exclusion region. The green and yellow bands indicate the $\pm $1 and 2 standard deviation ($\sigma $) uncertainties in the expected limit. The thin black lines show the effect of the theoretical uncertainties ($ \pm $1$ \sigma _{\mathrm {theory}}$) on the signal cross section. |
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Figure 12:
Observed exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^0_1}} $ and $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production for each individual analysis compared with the combination. The 4b search drives the exclusion at large values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ while the on-Z dilepton search and the multilepton search search are competing at lower values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $. |
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Figure 12-a:
Observed exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^0_1}} $ and $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production for each individual analysis compared with the combination. The 4b search drives the exclusion at large values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ while the on-Z dilepton search and the multilepton search search are competing at lower values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $. |
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Figure 12-b:
Observed exclusion contours at the 95% CL in the plane of $ {m_{\tilde{\chi}^0_1}} $ and $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production for each individual analysis compared with the combination. The 4b search drives the exclusion at large values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ while the on-Z dilepton search and the multilepton search search are competing at lower values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $. |
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Figure 13:
The analysis with the best expected exclusion limit at each point in the plane of $ {m_{\tilde{\chi}^0_1}} $ and $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production. |
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Figure 14:
The 95% CL upper limits on the production cross sections as a function of $ {m_{\tilde{\chi}^0_1}} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production with three choices of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ : (top) 0%, yielding the ZZ topology, (middle) 100%, yielding the HH topology, and (bottom) 50%, yielding the WH mixed topology. The solid black line represents the observed exclusion. The dashed black line represents the expected exclusion, while the green and yellow bands indicate the $\pm $1 and 2 standard deviation ($\sigma $) uncertainties in the expected limit. The red lines shows the theoretical cross section with its uncertainty. The other lines in each plot show the observed exclusion for individual analyses. |
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Figure 14-a:
The 95% CL upper limits on the production cross sections as a function of $ {m_{\tilde{\chi}^0_1}} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production with three choices of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ : 0%, yielding the ZZ topology. The solid black line represents the observed exclusion. The dashed black line represents the expected exclusion, while the green and yellow bands indicate the $\pm $1 and 2 standard deviation ($\sigma $) uncertainties in the expected limit. The red lines shows the theoretical cross section with its uncertainty. The other lines in each plot show the observed exclusion for individual analyses. |
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Figure 14-b:
The 95% CL upper limits on the production cross sections as a function of $ {m_{\tilde{\chi}^0_1}} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production with three choices of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ : 100%, yielding the HH topology. The solid black line represents the observed exclusion. The dashed black line represents the expected exclusion, while the green and yellow bands indicate the $\pm $1 and 2 standard deviation ($\sigma $) uncertainties in the expected limit. The red lines shows the theoretical cross section with its uncertainty. The other lines in each plot show the observed exclusion for individual analyses. |
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Figure 14-c:
The 95% CL upper limits on the production cross sections as a function of $ {m_{\tilde{\chi}^0_1}} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1} $ production with three choices of $ {\mathcal {B}(\tilde{\chi}^0_1 \to \mathrm{H} \tilde{\mathrm{G}})} $ : 50%, yielding the WH mixed topology. The solid black line represents the observed exclusion. The dashed black line represents the expected exclusion, while the green and yellow bands indicate the $\pm $1 and 2 standard deviation ($\sigma $) uncertainties in the expected limit. The red lines shows the theoretical cross section with its uncertainty. The other lines in each plot show the observed exclusion for individual analyses. |
| Tables | |
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Table 1:
Summary of all experimental searches considered in the combination (rows), and the signal topologies for which each search is used in the combined results (columns). |
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Table 2:
Definition of the search regions optimized for the WZ corridor region in the WZ signal topology. Events must have three leptons (e, $\mu$) forming at least one OSSF pair and they categorized in $ {m_{\ell \ell}} $, $ {M_\text {T}} $, $ {{p_{\mathrm {T}}} ^\text {miss}} $ and $ {H_{\mathrm {T}}} $. |
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Table 3:
Expected and observed yields in the search regions. For each bin, the first number corresponds to the expected yield and its total uncertainty while the second number gives the observation. |
| Summary |
|
A number of searches for the electroweak production of charginos and neutralinos predicted in supersymmetry (SUSY) have been performed in different final states. All searches considered here use proton-proton collision data at $\sqrt{s} = $ 13 TeV, recorded with the CMS detector at the CERN LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No significant deviations from the standard model expectation have been observed, as previously reported. An optimized search requiring three or more charged leptons (electrons or muons) has been presented, targeting chargino-neutralino production where the difference in mass between $ \tilde{\chi}^0_2 $ and $ \tilde{\chi}^0_1 $ is approximately equal to the mass of the Z boson, and no significant deviations from the standard model prediction are observed. This search is interpreted in a simplified model scenario of SUSY chargino-neutralino ($\tilde{\chi}^{\pm}_1 \tilde{\chi}^0_2 $) production with decays $\tilde{\chi}^{\pm}_1\to\mathrm{W}^{\pm}\tilde{\chi}^0_1$ and $ \tilde{\chi}^0_2 \to\mathrm{Z}\tilde{\chi}^0_1$, where $ \tilde{\chi}^0_1 $ is the lightest SUSY particle (LSP). In the targeted phase space, the expected and observed 95% confidence level exclusion limits extend to 255 GeV in the mass of $ \tilde{\chi}^0_2 $ and 125 GeV in the mass of $ \tilde{\chi}^0_1 $, improving the observed limits from the previous publication by up to 60 GeV [29]. A statistical combination of several searches is performed and interpreted in the context of simplified models of either chargino-neutralino production, or neutralino pair production in a gauge-mediated SUSY breaking (GMSB) scenario. For a massless LSP $ \tilde{\chi}^0_1 $ in the chargino-neutralino model, the combined result gives an observed (expected) limit in the $ \tilde{\chi}^{\pm}_1 $ mass of about 650 (570) GeV for the WZ topology, 480 (455) GeV for the WH topology, and 535 (440) GeV for the mixed topology. Compared to the results of individual analyses, the combination improves the observed exclusion limit by up to 40 GeV in the masses of $ \tilde{\chi}^{\pm}_1 $ and $ \tilde{\chi}^0_2 $ in the chargino-neutralino model. The combination also excludes intermediate mass values that were not excluded by individual analyses, including $ \tilde{\chi}^{\pm}_1 $ masses between 180 and 240 GeV in the WH topology. In the GMSB neutralino pair model, the combined result gives an observed (expected) limit in the $ \tilde{\chi}^0_1 $ mass of 650-750 (550-750) GeV. The combined result improves the observed limit by up to 200 GeV in the mass of $ \tilde{\chi}^0_1 $ in the GMSB neutralino pair model, depending on the branching fractions for the SUSY particle decays. |
| Additional Figures | |
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Additional Figure 1:
Exclusion contours at the 95% CL for the model of neutralino-neutralino production for events obtained in the 2-lep OS analysis. |
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Additional Figure 2:
Exclusion contours at the 95% CL for the model of neutralino-neutralino production for events obtained in the $\geq $3-lep analysis. |
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Additional Figure 3:
Exclusion contours at the 95% CL for the model of neutralino-neutralino production for events obtained in the bbbb analysis. |
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Additional Figure 4:
Exclusion contours at the 95% CL for the model of neutralino-neutralino production for events obtained in the $\mathrm {H}\rightarrow \gamma \gamma $ analysis. |
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