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| CMS-PAS-SUS-17-010 | ||
| Search for chargino pair production and top squark pair production in final states with two leptons in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| March 2018 | ||
| Abstract: A search for pair production of supersymmetric particles in events with two leptons (electrons or muons) and missing transverse momentum is reported. The data sample corresponds to 35.9 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}= $ 13 TeV collected by the CMS detector during the 2016 data taking period at the CERN LHC. The search targets two signal models for chargino and top squark pair production. No significant deviation is observed from the predicted background. The results are interpreted in terms of several simplified models assuming R-parity conservation and with the neutralino as the lightest supersymmetric particle. When the chargino is assumed to undergo a cascade decay through sleptons, exclusion limits at 95% confidence level are set on the mass of the chargino up to 800 GeV and on the mass of the neutralino up to 320 GeV. For the top squark production, the search focuses on models with a small mass difference between the top squark and the lightest neutralino. When the top squark decays into an off-shell top quark and a neutralino, the limits extend up to 420 and 360 GeV for the top squark and neutralino masses, respectively. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 11 (2018) 079. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Diagrams of the chargino pair production in two possible decay modes: the left plot shows decays through intermediate sleptons or sneutrinos, while the right one displays decays into a W boson and the lightest neutralino. |
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Figure 1-a:
Diagram of the chargino pair production in decay mode through intermediate sleptons or sneutrinos. |
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Figure 1-b:
Diagram of the chargino pair production in decay mode into a W boson and the lightest neutralino. |
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Figure 2:
Diagrams of the top squark-antisquark pair production with two possible decay modes for the top squark: the left plot shows decays into a top quark and the lightest neutralino, while the right one displays decays into a bottom quark and a chargino further decaying into a neutralino and a W boson. |
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Figure 2-a:
Diagram of the top squark-antisquark pair production in top squark decay mode into a top quark and the lightest neutralino. |
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Figure 2-b:
Diagram of the top squark-antisquark pair production in top squark decay mode into a bottom quark and a chargino further decaying into a neutralino and a W boson. |
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Figure 3:
Distributions of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV (left plots), 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV (middle) and $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV (right), for DF events without b-tagged jets but at least one jet (upper plots) and no jets (lower plots). The upper plot for the signal region with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV shows all the events without b-tagged jets regardless of their jet multiplicity. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 3-a:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for DF events without b-tagged jets but at least one jet. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 3-b:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for DF events without b-tagged jets but at least one jet. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 3-c:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV, for DF events without b-tagged jets regardless of their jet multiplicity. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 3-d:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for DF events with no jet. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 3-e:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for DF events with no jet. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 4:
Distributions of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV (left plots), 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV (middle) and $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV (right), for SF events without b-tagged jets but at least one jet (upper plots) and no jets (lower plots). The upper plot for the signal region with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV shows all the events without b-tagged jets regardless of their jet multiplicity. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 4-a:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for SF events without b-tagged jets but at least one jet. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 4-b:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for SF events without b-tagged jets but at least one jet. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 4-c:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV (right), for SF events without b-tagged jets regardless of their jet multiplicity. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 4-d:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for SF events with no jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 4-e:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the chargino signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for SF events with no jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 5:
Distributions of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV (left plots), 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV (middle), or $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV (right), for DF events with b-tagged jets (upper plots) and without b-tagged jets (lower plots). Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 5-a:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for DF events with b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 5-b:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for DF events with b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 5-c:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV, for DF events with b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 5-d:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for DF events without b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 5-e:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for DF events without b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 5-f:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV, for DF events without b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 6:
Distributions of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV (left plots), 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV (middle), or $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV (right), for SF events with b-tagged jets (upper plots) and without b-tagged jets (lower plots). Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 6-a:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for SF events with b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 6-b:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for SF events with b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 6-c:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV, for SF events with b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 6-d:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 140 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 200 GeV, for SF events without b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 6-e:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with 200 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV, for SF events without b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 6-f:
Distribution of $ {M_{\text {T2}}(\ell \ell)} $ after the fit to data in the top squark signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 300 GeV, for SF events without b-tagged jets. Expected total SM contributions before the fit (dark blue dashed line) and after a background+signal fit (dark red dotted line) are also shown. The ratio data/MC is shown for the expected total SM contribution after the fit using the only background hypothesis (black dots) and before any fit (dark blue dashed line). The hatched band represents the total uncertainty after the fit. |
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Figure 7:
Left: upper limits at 95% CL on the chargino pair production cross section as a function of the chargino and neutralino masses, when the chargino undergoes a cascade decay $ \tilde{ \chi }^{\pm}_1 \rightarrow \tilde{ \ell }\nu (\ell \tilde{ \nu })\rightarrow \ell \nu \tilde{ \chi }^{0}_1 $. The thick dashed red line shows the expected exclusion region in the plane ($m_{\tilde{ \chi }^{\pm}_1}, m_{\tilde{ \chi }^{0}_1}$). The thin dashed red lines show the variation of the exclusion regions due to the experimental uncertainties. The thick black line shows the observed exclusion region, while the thin black lines show the variation of the exclusion regions due to the theoretical uncertainties on the production cross section. Right: observed and expected upper limits at 95% CL as a function of the chargino mass for a neutralino mass of 1 GeV, assuming chargino decays into a neutralino and a W boson ($ \tilde{ \chi }^{\pm}_1 \rightarrow {\mathrm {W}} \tilde{ \chi }^{0}_1 $). |
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Figure 7-a:
Upper limits at 95% CL on the chargino pair production cross section as a function of the chargino and neutralino masses, when the chargino undergoes a cascade decay $ \tilde{ \chi }^{\pm}_1 \rightarrow \tilde{ \ell }\nu (\ell \tilde{ \nu })\rightarrow \ell \nu \tilde{ \chi }^{0}_1 $. The thick dashed red line shows the expected exclusion region in the plane ($m_{\tilde{ \chi }^{\pm}_1}, m_{\tilde{ \chi }^{0}_1}$). The thin dashed red lines show the variation of the exclusion regions due to the experimental uncertainties. The thick black line shows the observed exclusion region, while the thin black lines show the variation of the exclusion regions due to the theoretical uncertainties on the production cross section. |
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Figure 7-b:
Observed and expected upper limits at 95% CL as a function of the chargino mass for a neutralino mass of 1 GeV, assuming chargino decays into a neutralino and a W boson ($ \tilde{ \chi }^{\pm}_1 \rightarrow {\mathrm {W}} \tilde{ \chi }^{0}_1 $). |
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Figure 8:
Upper limits at 95% CL on the top squark production cross section as a function of the stop and neutralino masses. The plot on the left shows the results when top squark decays into a top quark and a neutralino are assumed. The plot on the right gives the limits for top squarks decaying into a bottom quark and a chargino, with the latter successively decaying into a W boson and a neutralino. The mass of the chargino is assumed to be equal to the average of the top squark and neutralino masses. The thick dashed red line shows the expected exclusion region in the plane ($m_{\tilde{ \mathrm{t} }}$, $m_{\tilde{ \chi }^{0}_1}$). The thin dashed red lines show the variation of the exclusion regions due to the experimental uncertainties. The thick black line shows the observed exclusion region, while the thin black lines show the variation of the exclusion regions due to the theoretical uncertainties on the production cross section. |
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Figure 8-a:
Upper limits at 95% CL on the top squark production cross section as a function of the stop and neutralino masses. The plot shows the results when top squark decays into a top quark and a neutralino are assumed. The thick dashed red line shows the expected exclusion region in the plane ($m_{\tilde{ \mathrm{t} }}$, $m_{\tilde{ \chi }^{0}_1}$). The thin dashed red lines show the variation of the exclusion regions due to the experimental uncertainties. The thick black line shows the observed exclusion region, while the thin black lines show the variation of the exclusion regions due to the theoretical uncertainties on the production cross section. |
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Figure 8-b:
Upper limits at 95% CL on the top squark production cross section as a function of the stop and neutralino masses. The plot gives the limits for top squarks decaying into a bottom quark and a chargino, with the latter successively decaying into a W boson and a neutralino. The mass of the chargino is assumed to be equal to the average of the top squark and neutralino masses. The thick dashed red line shows the expected exclusion region in the plane ($m_{\tilde{ \mathrm{t} }}$, $m_{\tilde{ \chi }^{0}_1}$). The thin dashed red lines show the variation of the exclusion regions due to the experimental uncertainties. The thick black line shows the observed exclusion region, while the thin black lines show the variation of the exclusion regions due to the theoretical uncertainties on the production cross section. |
| Tables | |
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Table 1:
Definition of the baseline selection used in the searches for chargino pair production and top squark pair production. |
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Table 2:
Definition of the signal regions for the chargino search as a function of the b jet multiplicity, ISR jet requirement, and the $ {{p_{\mathrm {T}}} ^\text {miss}} $ value. Also shown are the control regions with b-tagged jets used for the normalization of the $ \mathrm{ t \bar{t} } $ and tW backgrounds. Each of the regions is further divided in seven $ {M_{\text {T2}}(\ell \ell)} $ bins. |
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Table 3:
Definition of the signal regions for the top squark production search as a function of the b jet multiplicity, ISR jet requirement, and $ {{p_{\mathrm {T}}} ^\text {miss}} $ value. Each of the regions is further divided in seven $ {M_{\text {T2}}(\ell \ell)} $ bins. |
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Table 4:
Summary of the normalization scale factors for $ \mathrm{ t \bar{t} } $Z, WZ, and ZZ backgrounds in the signal regions used for the chargino (a) and top squark (b) searches. Uncertainties include the statistical uncertainties on data and simulated events, and the systematic uncertainties on the purity on the control regions. |
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Table 5:
Size of systematic uncertainties in the predicted yields for SM processes. The first column shows the range of the uncertainties in the global background normalization across the different signal regions, while the second one gives the effect on the $ {M_{\text {T2}}(\ell \ell)} $ shape. |
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Table 6:
Observed and expected yields of DF events in the signal regions for the chargino search. The quoted uncertainty on the background predictions includes statistical and systematic contributions. |
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Table 7:
Observed and expected yields of SF events in the signal regions for the chargino search. The quoted uncertainty on the background predictions includes statistical and systematic contributions. |
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Table 8:
Observed and expected yields of DF events in the signal regions for the top squark search. The quoted uncertainty on the background predictions includes statistical and systematic contributions. |
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Table 9:
Observed and expected yields of SF events in the signal regions for the top squark search. The quoted uncertainty on the background predictions includes statistical and systematic contributions. |
| Summary |
|
A search has been presented for new physics in events with two oppositely charged isolated leptons and missing transverse momentum in 35.9 fb$^{-1}$ of proton-proton collision data collected by the CMS detector during the 2016 run of the LHC operation at a center-of-mass energy of 13 TeV. No evidence for a deviation with respect to SM predictions was observed in data, and the results have been used to set upper limits on the cross section of supersymmetric particle production for several simplified supersymmetric model spectra. The chargino pair production has been investigated in two possible decay modes. If the chargino is assumed to undergo a cascade decay through sleptons, an exclusion region in the ($m_{\tilde{\chi}^{\pm}_1}, m_{\tilde{\chi}^0_1}$) plane can be derived, extending till chargino masses of 800 GeV and neutralino masses of 320 GeV. These are the most stringent limits on this model to date. For chargino decays into a neutralino and a W boson, limits on production cross section have been derived assuming a neutralino mass of 1 GeV, and chargino masses in the range 170-200 GeV have been excluded. Top squark pair production was also tested, with a focus on compressed decay modes. A model with the top squark decaying into a top quark and a neutralino was considered. In the region where $m_{\mathrm{W}} < m_{\tilde{\mathrm{t}}}-m_{\tilde{\chi}^0_1} \lesssim m_{\mathrm{t}}$, top squark masses are excluded up to about 420 GeV. An alternative model has also been considered, where the top squark decays into a chargino and a bottom quark, with the chargino subsequently decaying into a W boson and the lightest neutralino. The results extend the previous exclusion region in the dilepton channel [27] in the compressed region where 175 $ \lesssim m_{\tilde{\mathrm{t}}}-m_{\tilde{\chi}^0_1} \lesssim $ 225 GeV up to a top squark mass of about 500 GeV. |
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