CMS-SUS-17-004 ; CERN-EP-2017-283 | ||
Combined search for electroweak production of charginos and neutralinos in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
11 January 2018 | ||
JHEP 03 (2018) 160 | ||
Abstract: A statistical combination of several searches for the electroweak production of charginos and neutralinos is presented. All searches use proton-proton collision data at $\sqrt{s} = $ 13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. In addition to the combination of previous searches, a targeted analysis requiring three or more charged leptons (electrons or muons) is presented, focusing on the challenging scenario in which 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 chargino-neutralino or neutralino pair production. For chargino-neutralino production, in the case when the lightest neutralino is massless, the combination yields an observed (expected) limit at the 95% confidence level on the chargino mass of up to 650 (570) GeV, improving upon the individual analysis limits 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 targeted search requiring three or more leptons obtains observed and expected exclusion limits of around 225 GeV on the second neutralino mass and 125 GeV on the lightest neutralino mass, improving the observed limit by about 60 GeV in both masses compared to the previous CMS result. In the neutralino pair production model, the combined observed (expected) exclusion limit on the neutralino mass extends up to 650-750 (550-750) GeV, depending on the branching fraction assumed. This extends the observed exclusion achieved in the individual analyses by up to 200 GeV. The combined result additionally excludes some intermediate gaps in the mass coverage of the individual analyses. | ||
Links: e-print arXiv:1801.03957 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; |
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:
Production of $ \tilde{\chi}^{\pm}_{1} \tilde{\chi}^0_2 $ with the $ \tilde{\chi}^{\pm}_{1} $ decaying to a W boson and the LSP, $ \tilde{\chi}^0_1 $, and the $ \tilde{\chi}^0_2 $ decaying to either (left) a Z boson and the $ \tilde{\chi}^0_1 $ or (right) a H boson and the $ \tilde{\chi}^0_1 $. |
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Figure 1-a:
Production of $ \tilde{\chi}^{\pm}_{1} \tilde{\chi}^0_2 $ with the $ \tilde{\chi}^{\pm}_{1} $ decaying to a W boson and the LSP, $ \tilde{\chi}^0_1 $, and the $ \tilde{\chi}^0_2 $ decaying to a Z boson and the $ \tilde{\chi}^0_1 $. |
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Figure 1-b:
Production of $ \tilde{\chi}^{\pm}_{1} \tilde{\chi}^0_2 $ with the $ \tilde{\chi}^{\pm}_{1} $ decaying to a W boson and the LSP, $ \tilde{\chi}^0_1 $, and the $ \tilde{\chi}^0_2 $ decaying to a H boson and the $ \tilde{\chi}^0_1 $. |
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Figure 2:
A GMSB model with $ \tilde{\chi}^0_1 \tilde{\chi}^0_1 $ pair production. The two $ \tilde{\chi}^0_1 $ particles decay into the $ \tilde{G} $ LSP and (left) both to Z bosons, (center) a Z and a H boson, or (right) both to H bosons. |
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Figure 2-a:
A GMSB model with $ \tilde{\chi}^0_1 \tilde{\chi}^0_1 $ pair production. The two $ \tilde{\chi}^0_1 $ particles decay into the $ \tilde{G} $ LSP and both to Z bosons. |
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Figure 2-b:
A GMSB model with $ \tilde{\chi}^0_1 \tilde{\chi}^0_1 $ pair production. The two $ \tilde{\chi}^0_1 $ particles decay into the $ \tilde{G} $ LSP and to a Z and a H boson. |
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Figure 2-c:
A GMSB model with $ \tilde{\chi}^0_1 \tilde{\chi}^0_1 $ pair production. The two $ \tilde{\chi}^0_1 $ particles decay into the $ \tilde{G} $ LSP and both to 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, calculated to NLO accuracy in QCD with Resummino [56]. The $ \tilde{\chi}^{\pm}_{1} $ and $ \tilde{\chi}^0_2 $ are assumed to be mass-degenerate winos. 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, from the variation of renormalization and factorization scales as well as parton density functions, 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 $ \tilde{\chi}^0_1 $ LSPs with large Lorentz boost. |
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Figure 4-a:
Distribution 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 $ \tilde{\chi}^0_1 $ LSPs with large Lorentz boost. |
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Figure 4-b:
Distribution 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 $ \tilde{\chi}^0_1 $ LSPs with large Lorentz boost. |
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Figure 5:
Distributions of the transverse mass of the third lepton with respect to $ {{p_{\mathrm {T}}} ^\text {miss}} $ (upper left), the $ {{p_{\mathrm {T}}} ^\text {miss}} $ (upper right), the $ {m_{\ell \ell}} $ of the OSSF pair (lower left), and the $ {H_{\mathrm {T}}} $ (lower right). Distributions for two signal mass points in the WZ corridor are overlaid for illustration. The bottom panel shows the ratio of observed data to predicted yields. The dark purple band shows the statistical uncertainty in the background prediction, while the light blue band shows the total uncertainty. |
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Figure 5-a:
Distribution of the transverse mass of the third lepton with respect to $ {{p_{\mathrm {T}}} ^\text {miss}} $. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. The bottom panel shows the ratio of observed data to predicted yields. The dark purple band shows the statistical uncertainty in the background prediction, while the light blue band shows the total uncertainty. |
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Figure 5-b:
Distribution of the $ {{p_{\mathrm {T}}} ^\text {miss}} $. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. The bottom panel shows the ratio of observed data to predicted yields. The dark purple band shows the statistical uncertainty in the background prediction, while the light blue band shows the total uncertainty. |
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Figure 5-c:
Distribution of the $ {m_{\ell \ell}} $ of the OSSF pair. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. The bottom panel shows the ratio of observed data to predicted yields. The dark purple band shows the statistical uncertainty in the background prediction, while the light blue band shows the total uncertainty. |
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Figure 5-d:
Distribution of the $ {H_{\mathrm {T}}} $. Distributions for two signal mass points in the WZ corridor are overlaid for illustration. The bottom panel shows the ratio of observed data to predicted yields. The dark purple band shows the statistical uncertainty in the background prediction, while the light blue band shows the total uncertainty. |
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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. The bottom panel shows the ratio of observed data to predicted yields. The dark purple band shows the statistical uncertainty in the background prediction, while the light blue band shows the total uncertainty. |
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Figure 7:
The 95% confidence level 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 lines indicate the $ \pm $1$ \sigma _{\text {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties (${\pm}$1$\sigma _{\text {theory}}$) on the signal cross section. The color scale 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 (upper) the WZ topology, (middle) the WH topology, or (lower) 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 lines indicate the $ \pm $1$ \sigma _{\text {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm $1$ \sigma _{\text {theory}}$) on the signal cross section. The color scale 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 lines indicate the $ \pm $1$ \sigma _{\text {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm $1$ \sigma _{\text {theory}}$) on the signal cross section. The color scale 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 lines indicate the $ \pm $1$ \sigma _{\text {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm $1$ \sigma _{\text {theory}}$) on the signal cross section. The color scale 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 lines indicate the $ \pm $1$ \sigma _{\text {experiment}}$ uncertainty. The thin black lines show the effect of the theoretical uncertainties ($ \pm $1$ \sigma _{\text {theory}}$) on the signal cross section. The color scale 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 (upper) the WZ topology, (middle) the WH topology, and (lower) 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. Figure 9-c |
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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 (upper) the WZ topology, (middle) the WH topology, and (lower) the mixed topology 50% branching fraction to each of WZ and WH. |
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Figure 10:
Exclusion contours at 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 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 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{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 $1 and 2$\sigma $ uncertainties in the expected limit. The thin black lines show the effect of the theoretical uncertainties (${\pm}$1$\sigma _{\text {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{G})} $ for the model of $ {\tilde{\chi}^0_1 \tilde{\chi}^0_1 } $ production for each individual analysis compared with the combination. For the 4 b contour, the region above is excluded, while for all others, the region to the left is excluded. The 4 b search drives the exclusion at large values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to {\mathrm {H}} \tilde{G})} $ while the on- Z dilepton and multilepton searches are competing at lower values of $ {\mathcal {B}(\tilde{\chi}^0_1 \to {\mathrm {H}} \tilde{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{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{G})} $ : (upper) 0%, yielding the ZZ topology, (middle) 100%, yielding the ZH topology, and (lower) 50%, yielding the ZH 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 $1 and 2$\sigma $ uncertainties in the expected limit. The red line 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 the 0% choice of $ {\mathcal {B}(\tilde{\chi}^0_1 \to {\mathrm {H}} \tilde{G})} $, 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 $1 and 2$\sigma $ uncertainties in the expected limit. The red line 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 the 100% choice of $ {\mathcal {B}(\tilde{\chi}^0_1 \to {\mathrm {H}} \tilde{G})} $, yielding the ZH 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 $1 and 2$\sigma $ uncertainties in the expected limit. The red line 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 the 50% choice of $ {\mathcal {B}(\tilde{\chi}^0_1 \to {\mathrm {H}} \tilde{G})} $, yielding the ZH 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 $1 and 2$\sigma $ uncertainties in the expected limit. The red line 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). The searches are described in Sections 5.1 through 5.6 and Section 6. The ${\geq}$3$\ell $ search described in Section 5.5 is used for all signal topologies except for WZ, where the reoptimized search strategy from Section 6 is employed instead. |
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Table 2:
Definition of the search regions (SRs) optimized for the WZ corridor in the WZ signal topology. Events must have three leptons ( e, ${{\mu}}$) forming at least one OSSF pair and they are categorized in $ {m_{\ell \ell}} $, $ {M_\text {T}} $, $ {{p_{\mathrm {T}}} ^\text {miss}} $ and $ {H_{\mathrm {T}}} $. Where ranges of values are given, the lower bound is inclusive while the upper bound is exclusive, e.g., $75 \leq {m_{\ell \ell}} < $ 105 GeV. |
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Table 3:
Expected and observed event 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. Where ranges of values are given for the selections, the lower bound is inclusive while the upper bound is exclusive, e.g., 75 $ \leq {m_{\ell \ell}} < $ 105 GeV. |
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 LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No significant deviations from the standard model expectations have been observed. A targeted search requiring three or more charged leptons (electrons or muons) has been presented, focusing on 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 predictions 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 225 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 [38]. 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. These results represent the most stringent constraints to date for all models considered. |
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$\ell $ on-Z 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 $3$\ell $ 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 4b 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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Additional Figure 5:
The correlation matrix for the background predictions in the 3 lepton SRs. |
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