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| CMS-PAS-SUS-16-025 | ||
| Search for new physics in the compressed mass spectra scenario using events with two soft opposite-sign leptons and missing transverse momentum at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| August 2016 | ||
|
Abstract:
A search for new physics in events with two low-momentum opposite-sign leptons and missing transverse momentum is presented using 12.9 fb$^{-1}$ of data collected at 13 TeV in 2016. The observed data yields are compatible with the predictions for standard model processes. The results are interpreted in the context of supersymmetry with compressed mass spectra, described in the form of simplified models. In the first model the lightest chargino ($\tilde{\chi}_1^{\pm}$) and the second-lightest neutralino ($\tilde{\chi}_2^{0}$) are pair produced and degenerate in mass, and decay to the lightest neutralino and a virtual W and Z boson, respectively. At 95% confidence level, $\tilde{\chi}_1^{\pm}$/$\tilde{\chi}_2^{0}$ masses are excluded up to 165 GeV for a mass difference of 7.5 GeV with respect to the lightest neutralino. Previously such a scenario had only been constrained by LEP experiments. The results are also interpreted in a simplified model of top squark pair production for the case that the mass difference between the top squark and the lightest neutralino is below the mass of the W boson. This document has been revised with respect to the version dated August 6, 2016. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Additional information on efficiencies needed for reinterpretation of these results are available here. |
| Figures | |
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Figure 1:
Left: electroweakino pair production. Right: $\tilde{ \mathrm{ t } }$ four-body decay. The model used to interpret the results represents a simplified version of the four body decay in which the top quark decay width is neglected. |
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Figure 1-a:
Electroweakino pair production. |
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Figure 1-b:
$\tilde{ \mathrm{ t } }$ four-body decay. The model used to interpret the results represents a simplified version of the four body decay in which the top quark decay width is neglected. |
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Figure 2:
M$(\ell \ell )$ distributions for DY+jets (top) and $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ (bottom) control regions. Left: control regions with low $ {E_{\mathrm {T}}^{\text {miss}}} $. Right: control regions with high $ {E_{\mathrm {T}}^{\text {miss}}} $. The bands in data/prediction ratio reflect the statistical uncertainty on the simulation. |
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Figure 2-a:
M$(\ell \ell )$ distribution for the DY+jets control region with low $ {E_{\mathrm {T}}^{\text {miss}}} $. The bands in data/prediction ratio reflect the statistical uncertainty on the simulation. |
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Figure 2-b:
M$(\ell \ell )$ distribution for the DY+jets control region with high $ {E_{\mathrm {T}}^{\text {miss}}} $. The bands in data/prediction ratio reflect the statistical uncertainty on the simulation. |
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Figure 2-c:
M$(\ell \ell )$ distribution for the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ control region with low $ {E_{\mathrm {T}}^{\text {miss}}} $. The bands in data/prediction ratio reflect the statistical uncertainty on the simulation. |
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Figure 2-d:
M$(\ell \ell )$ distribution for the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ control region with high $ {E_{\mathrm {T}}^{\text {miss}}} $. The bands in data/prediction ratio reflect the statistical uncertainty on the simulation. |
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Figure 3:
Dilepton mass distributions in data, compared with the SM predictions, in electroweakino-like signal region for two $ {E_{\mathrm {T}}^{\text {miss}}} $ ranges: 125 $< {E_{\mathrm {T}}^{\text {miss}}} <$ 200 GeV (muon channel) (left) and $ {E_{\mathrm {T}}^{\text {miss}}} > $ 200 GeV (muon and electron channels) (right) for 10.1 fb$^{-1}$ and 12.9 fb$^{-1}$ of integrated luminosity, respectively. The shaded grey band in the SM prediction is the total uncertainty, calculated from the statistical uncertainties in the data application regions and the systematic uncertainty for each SM background yield. In the ratio plot the light purple band indicates the statistical uncertainty, while the light cyan band includes both statistical and systematic uncertainties. The signal corresponding to $\tilde{\chi}^0 _2\tilde{\chi}^{\pm} _1 \rightarrow \tilde{\chi}^0 _1\tilde{\chi}^0 _1 \mathrm{ZW^{*}}$ for a $\tilde{\chi}^0 _2$ mass of 100 GeV and a difference ($\Delta m$) between $\tilde{\chi}^{0} _2$ and $\tilde{\chi}^{0} _1$ of 20 GeV is superimposed. |
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Figure 3-a:
Dilepton mass distribution in data, compared with the SM predictions, in electroweakino-like signal region125 $< {E_{\mathrm {T}}^{\text {miss}}} <$ 200 GeV (muon channel), for 10.1 fb$^{-1}$ of integrated luminosity. The shaded grey band in the SM prediction is the total uncertainty, calculated from the statistical uncertainties in the data application regions and the systematic uncertainty for each SM background yield. In the ratio plot the light purple band indicates the statistical uncertainty, while the light cyan band includes both statistical and systematic uncertainties. The signal corresponding to $\tilde{\chi}^0 _2\tilde{\chi}^{\pm} _1 \rightarrow \tilde{\chi}^0 _1\tilde{\chi}^0 _1 \mathrm{ZW^{*}}$ for a $\tilde{\chi}^0 _2$ mass of 100 GeV and a difference ($\Delta m$) between $\tilde{\chi}^{0} _2$ and $\tilde{\chi}^{0} _1$ of 20 GeV is superimposed. |
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Figure 3-b:
Dilepton mass distributions in data, compared with the SM predictions, in electroweakino-like signal region for $ {E_{\mathrm {T}}^{\text {miss}}} > $ 200 GeV (muon and electron channels) for 12.9 fb$^{-1}$ of integrated luminosity, respectively. The shaded grey band in the SM prediction is the total uncertainty, calculated from the statistical uncertainties in the data application regions and the systematic uncertainty for each SM background yield. In the ratio plot the light purple band indicates the statistical uncertainty, while the light cyan band includes both statistical and systematic uncertainties. The signal corresponding to $\tilde{\chi}^0 _2\tilde{\chi}^{\pm} _1 \rightarrow \tilde{\chi}^0 _1\tilde{\chi}^0 _1 \mathrm{ZW^{*}}$ for a $\tilde{\chi}^0 _2$ mass of 100 GeV and a difference ($\Delta m$) between $\tilde{\chi}^{0} _2$ and $\tilde{\chi}^{0} _1$ of 20 GeV is superimposed. |
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Figure 4:
$ {p_{\mathrm {T}}} $ distributions for the leading lepton in data, compared with the SM predictions, in $\tilde{ \mathrm{ t } } $-like signal region for two $ {E_{\mathrm {T}}^{\text {miss}}} $ ranges: 125 $< {E_{\mathrm {T}}^{\text {miss}}} <$ 200 GeV (muon channel) (left) and $ {E_{\mathrm {T}}^{\text {miss}}} >$ 200 GeV (muon and electron channels) (right) for 10.1 fb$^{-1}$ and 12.9 fb$^{-1}$ of integrated luminosity, respectively. The shaded grey band in the SM prediction is the total uncertainty, calculated from the statistical uncertainties in the data application regions and the systematic uncertainty for each SM background yield. In the ratio plot the light purple band indicates the statistical uncertainty, while the light cyan band includes both statistical and systematic uncertainties. The signal corresponds to the model of $\tilde{ \mathrm{ t } }$ pair production described in the text, where the $\tilde{ \mathrm{ t } }$ mass is 350 GeV and $\Delta m(\tilde{ \mathrm{ t } },\tilde{\chi}^{0} _1)$ is 20 GeV. |
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Figure 4-a:
$ {p_{\mathrm {T}}} $ distribution for the leading lepton in data, compared with the SM predictions, in $\tilde{ \mathrm{ t } } $-like signal region for 125 $< {E_{\mathrm {T}}^{\text {miss}}} <$ 200 GeV (muon channel) for 10.1 fb$^{-1}$ of integrated luminosity, respectively. The shaded grey band in the SM prediction is the total uncertainty, calculated from the statistical uncertainties in the data application regions and the systematic uncertainty for each SM background yield. In the ratio plot the light purple band indicates the statistical uncertainty, while the light cyan band includes both statistical and systematic uncertainties. The signal corresponds to the model of $\tilde{ \mathrm{ t } }$ pair production described in the text, where the $\tilde{ \mathrm{ t } }$ mass is 350 GeV and $\Delta m(\tilde{ \mathrm{ t } },\tilde{\chi}^{0} _1)$ is 20 GeV. |
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Figure 4-b:
$ {p_{\mathrm {T}}} $ distributions for the leading lepton in data, compared with the SM predictions, in $\tilde{ \mathrm{ t } } $-like signal region for $ {E_{\mathrm {T}}^{\text {miss}}} >$ 200 GeV (muon and electron channels) for 12.9 fb$^{-1}$ of integrated luminosity, respectively. The shaded grey band in the SM prediction is the total uncertainty, calculated from the statistical uncertainties in the data application regions and the systematic uncertainty for each SM background yield. In the ratio plot the light purple band indicates the statistical uncertainty, while the light cyan band includes both statistical and systematic uncertainties. The signal corresponds to the model of $\tilde{ \mathrm{ t } }$ pair production described in the text, where the $\tilde{ \mathrm{ t } }$ mass is 350 GeV and $\Delta m(\tilde{ \mathrm{ t } },\tilde{\chi}^{0} _1)$ is 20 GeV. |
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Figure 5:
The observed exclusion contours (black curves) assuming the NLO+NLL cross sections, with the corresponding 1 standard deviation uncertainties for electroweak (left) and $\tilde{ \mathrm{ t } }$ (right) searches. The dashed (red) curves present the expected limits with 1 and 2 standard deviation experimental uncertainties. Results are based on a simplified model of $\tilde{\chi}^0 _2\tilde{\chi}^{\pm} _1\rightarrow \tilde{\chi}^0 _1\tilde{\chi}^0 _1 \mathrm{ Z^{*}W^{*} } $ process with a pure Wino production cross section in the electroweak analysis, while a simplified model of the $\tilde{ \mathrm{ t } }$ pair production, followed by the $\tilde{\mathrm{t}} \rightarrow \mathrm{ ffb } \tilde{\chi}^0 _1$ decay is used for the $\tilde{ \mathrm{ t } }$ analysis. Data corresponds to an integrated luminosity ranging from 10.1 fb$^{-1}$ to 12.9 fb$^{-1}$. |
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Figure 5-a:
The observed exclusion contours (black curves) assuming the NLO+NLL cross sections, with the corresponding 1 standard deviation uncertainties for the electroweak search. The dashed (red) curves present the expected limits with 1 and 2 standard deviation experimental uncertainties. Results are based on a simplified model of $\tilde{\chi}^0 _2\tilde{\chi}^{\pm} _1\rightarrow \tilde{\chi}^0 _1\tilde{\chi}^0 _1 \mathrm{ Z^{*}W^{*} } $ process with a pure Wino production cross section in the electroweak analysis, while a simplified model of the $\tilde{ \mathrm{ t } }$ pair production, followed by the $\tilde{\mathrm{t}} \rightarrow \mathrm{ ffb } \tilde{\chi}^0 _1$ decay is used for the $\tilde{ \mathrm{ t } }$ analysis. Data corresponds to an integrated luminosity ranging from 10.1 fb$^{-1}$ to 12.9 fb$^{-1}$. |
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Figure 5-b:
The observed exclusion contours (black curves) assuming the NLO+NLL cross sections, with the corresponding 1 standard deviation uncertainties for the $\tilde{ \mathrm{ t } }$ search. The dashed (red) curves present the expected limits with 1 and 2 standard deviation experimental uncertainties. Results are based on a simplified model of $\tilde{\chi}^0 _2\tilde{\chi}^{\pm} _1\rightarrow \tilde{\chi}^0 _1\tilde{\chi}^0 _1 \mathrm{ Z^{*}W^{*} } $ process with a pure Wino production cross section in the electroweak analysis, while a simplified model of the $\tilde{ \mathrm{ t } }$ pair production, followed by the $\tilde{\mathrm{t}} \rightarrow \mathrm{ ffb } \tilde{\chi}^0 _1$ decay is used for the $\tilde{ \mathrm{ t } }$ analysis. Data corresponds to an integrated luminosity ranging from 10.1 fb$^{-1}$ to 12.9 fb$^{-1}$. |
| Tables | |
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Table 1:
Selection requirements for the signal regions. The subleading lepton $ {p_{\mathrm {T}}} $ threshold is reduced to 3.5 GeV for muons in the high $ {E_{\mathrm {T}}^{\text {miss}}} $ $\tilde{ \mathrm{ t } } $-like signal region. $Iso_{\text {rel}}$ and $Iso_{\text {abs}}$ are relative and absolue isolation. |
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Table 2:
Summary of selection of control regions and the WW validation region (VR). |
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Table 3:
Data and simulation yields for the DY and $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ control regions corresponding to a integrated luminosity of 12.9 fb$^{-1}$ (high $ {E_{\mathrm {T}}^{\text {miss}}} $ region) and 10.1 fb$^{-1}$ (low $ {E_{\mathrm {T}}^{\text {miss}}} $ region). Uncertainties are statistical. |
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Table 4:
Typical relative uncertainties on the yields estimated with the background prediction methods in the signal region for each individual systematic uncertainty source. |
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Table 5:
Predicted and data yields for electroweakino-like SR for 12.9 fb$^{-1}$ and 10.1 fb$^{-1}$ of integrated luminosity. Predicted yields and total uncertainties are reported. |
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Table 6:
Predicted and data yields for $\tilde{ \mathrm{ t } } $-like SR for 12.9 fb$^{-1}$ and 10.1 fb$^{-1}$ of integrated luminosity. Predicted yields and total uncertainties are reported. |
| Summary |
| A search for new physics in events with two soft opposite-sign leptons and missing transverse energy is presented using the data collected at 13 TeV in 2016 corresponding to an integrated luminosity of up to 12.9 fb$^{-1}$. The data is consistent with the standard model expectations. The results are interpreted in the framework of supersymmetric simplified models targeting electroweakino mass-degenerate spectra and in terms of $\tilde{\mathrm{t}}$-$\tilde{\chi}^{0}_1$ mass-degenerate benchmarks. For the first time since LEP experiments a search probes the $\tilde{\chi}^{0}_2\tilde{\chi}^{\pm}_1\rightarrow \tilde{\chi}^{0}_1\tilde{\chi}^{0}_1 \mathrm{ Z^{*}W^{*}}$ process for mass differences ($\Delta m$) between $\tilde{\chi}^{0}_2$ and $\tilde{\chi}^{0}_1$ of less than 20 GeV. Assuming Wino production cross sections, $\tilde{\chi}^{0}_2$ masses up to 195 GeV for a $\Delta$m of 20 GeV and up to 165 GeV for a $\Delta m$ of 7.5 GeV are excluded. For the $\tilde{\mathrm{t}}$ four body decay, $\tilde{\mathrm{t}}$ masses of up to 360 GeV are excluded for a $\Delta m(\tilde{\mathrm{t}},\tilde{\chi}^{0}_1) =$ 30 GeV within the simplified model. |
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Compact Muon Solenoid LHC, CERN |
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