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| CMS-SUS-16-042 ; CERN-EP-2017-201 | ||
| Search for supersymmetry in events with one lepton and multiple jets exploiting the angular correlation between the lepton and the missing transverse momentum in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 28 September 2017 | ||
| Phys. Lett. B 780 (2018) 384 | ||
| Abstract: Results are presented from a search for supersymmetry in events with a single electron or muon and hadronic jets. The data correspond to a sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV with an integrated luminosity of 35.9 fb$^{-1}$, recorded in 2016 by the CMS experiment. A number of exclusive search regions are defined according to the number of jets, the number of b-tagged jets, the scalar sum of the transverse momenta of the jets, and the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. Standard model background events are reduced significantly by requiring a large azimuthal angle between the direction of the lepton and of the reconstructed W boson, computed under the hypothesis that all of the missing transverse momentum in the event arises from a neutrino produced in the leptonic decay of the W boson. The numbers of observed events are consistent with the expectations from standard model processes, and the results are used to set lower limits on supersymmetric particle masses in the context of two simplified models of gluino pair production. In the first model, where each gluino decays to a top quark-antiquark pair and a neutralino, gluino masses up to 1.8 TeV are excluded at the 95% CL. The second model considers a three-body decay to a light quark-antiquark pair and a chargino, which subsequently decays to a W boson and a neutralino. In this model, gluinos are excluded up to 1.9 TeV. | ||
| Links: e-print arXiv:1709.09814 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures & Tables | Summary | Additional Figures & Tables | 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:
Diagrams showing the simplified models (left) T1tttt and (right) T5qqqqWW. |
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Figure 1-a:
Diagram showing the T1tttt simplified model. |
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Figure 1-b:
Diagram showing the T5qqqqWW simplified model. |
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Figure 2:
Comparison of the $ {\Delta \phi} $ distribution for (left) the multi-b and (right) the 0-b analysis for two of the search bins given in Table xxxxx. The simulated background events are stacked on top of each other and several signal points are overlaid for illustration. The wider bins are normalized to a bin width of 0.1. The ratio of data to simulation is given in the lower panels. |
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Figure 2-a:
Comparison of the $ {\Delta \phi} $ distribution for the multi-b analysis for two of the search bins given in Table xxxxx. The simulated background events are stacked on top of each other and several signal points are overlaid for illustration. The wider bins are normalized to a bin width of 0.1. The ratio of data to simulation is given in the lower panels. |
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Figure 2-b:
Comparison of the $ {\Delta \phi} $ distribution for the 0-b analysis for two of the search bins given in Table xxxxx. The simulated background events are stacked on top of each other and several signal points are overlaid for illustration. The wider bins are normalized to a bin width of 0.1. The ratio of data to simulation is given in the lower panels. |
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Figure 3:
Multi-b search: comparison of the numbers of events observed in the data and the numbers expected from the estimated SM backgrounds in the 39 search bins defined in the text, with details given in Table yyyyy. Upper panel: the data are represented by black points with error bars, while the total SM background expected is shown as a hatched region that represents the uncertainty. For illustration, the relative fraction of the different SM background contributions determined in simulation is shown by the stacked, colored histograms, normalized so that their sum is equal to the background estimated using data control regions, as described in the text. The expected event yields for two T1tttt SUSY benchmark models are represented by the open histograms. Lower panel: the ratio of the number of events observed in data to the number of events expected from the SM background in each search bin. The error bars on the data points indicate the statistical uncertainty in the ratio, while the gray hatched region indicates the uncertainty on this ratio from the uncertainty in the background estimate. |
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Figure 4:
0-b search: comparison of the numbers of events observed in the data and the numbers expected from the estimated SM backgrounds in the 28 search bins defined in the text, with details given in Table zzzzz. Upper panel: the data are represented by black points with error bars, while the total SM background expected is shown as a hatched region that represents the uncertainty. The filled, stacked histograms represent the predictions for ${{\mathrm{t} {}\mathrm{\bar{t}}}}$+jets, W+jets events, and the remaining backgrounds. The expected yields from two T5qqqqWW SUSY benchmark models are represented as solid lines. Lower panel: the ratio of the number of events observed in data to the number of events expected from the SM background in each search bin. The error bars on the data points indicate the statistical uncertainty in the ratio, while the gray hatched region indicates the uncertainty on this ratio from the uncertainty in the background estimate. |
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Figure 5:
Cross section limits at a 95% CL for the (left) T1tttt and (right) T5qqqqWW models, as a function of the gluino and LSP masses. In T5qqqqWW, the pair-produced gluinos decay to first- or second-generation quark-antiquark pairs (${\mathrm{q} \mathrm{\bar{q}}}$) and a chargino ($\tilde{\chi}^{\pm}_1$) with its mass taken to be $m_{\tilde{\chi}^{\pm}_1}=0.5(m_{{\mathrm{\widetilde{g}}}}+m_{\tilde{\chi}^0_1})$. The solid black (dashed red) lines correspond to the observed (expected) mass limits, with the thicker lines representing the central values and the thinner lines representing the limits of 68% uncertainty bands related to the theoretical (experimental) uncertainties. |
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Figure 5-a:
Cross section limits at a 95% CL for the T1tttt model, as a function of the gluino and LSP masses. The solid black (dashed red) lines correspond to the observed (expected) mass limits, with the thicker lines representing the central values and the thinner lines representing the limits of 68% uncertainty bands related to the theoretical (experimental) uncertainties. |
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Figure 5-b:
Cross section limits at a 95% CL for the T5qqqqWW model, as a function of the gluino and LSP masses. The pair-produced gluinos decay to first- or second-generation quark-antiquark pairs (${\mathrm{q} \mathrm{\bar{q}}}$) and a chargino ($\tilde{\chi}^{\pm}_1$) with its mass taken to be $m_{\tilde{\chi}^{\pm}_1}=0.5(m_{{\mathrm{\widetilde{g}}}}+m_{\tilde{\chi}^0_1})$. The solid black (dashed red) lines correspond to the observed (expected) mass limits, with the thicker lines representing the central values and the thinner lines representing the limits of 68% uncertainty bands related to the theoretical (experimental) uncertainties. |
| Tables | |
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Table 1:
Overview of the definitions of the various regions and samples employed in the analysis. For the QCD fit the electron (e) sample is used, while for the determination (det.) of $ {R_{\mathrm {CS}}} (\mathrm{W^{\pm}})$ the muon ($\mu $) sample is used. Regions corresponding to blank cells are not used in the analysis. |
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Table 2:
Summary of systematic uncertainties in the total background estimates for the multi-b and for the 0-b analyses. |
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Table 3:
Summary of the systematic uncertainties and their average effect on the yields for the benchmark points defined in the text. The values, which are quite similar for the multi-b and the 0-b analyses, are usually larger for compressed scenarios, where the mass difference between the gluino and the lightest neutralino is small. |
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Table 4:
Definition of search bins and naming convention in the multi-b search. Also given are the $ {\Delta \phi} $ values that are used to define the CRs and the SRs, the numbers of expected background events with combined statistical and systematic uncertainties, the observed numbers of events, and the expected numbers of signal events in the multi-b search bins. |
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Table 5:
Definition of search bins and naming convention in the 0-b search. Also given are the $ {\Delta \phi} $ values that are used to define the CRs and the SRs, the numbers of expected background events with combined statistical and systematic uncertainties, the observed numbers of events, and the expected numbers of signal events in the 0-b search bins. |
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Table 6:
Numbers of expected background events with combined statistical and systematic uncertainty and the observed numbers of events in aggregated search bins. The expected number of signal events for the two corresponding benchmark signals for the multi-b and 0-b analyses, respectively, are given as well. |
| Summary |
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A search for supersymmetry has been performed using a 35.9 fb$^{-1}$ sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV, recorded by the CMS experiment in 2016. Several exclusive search bins are defined that differ in the number of jets, the number of b-tagged jets, the scalar sum of all jet transverse momenta as well as the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. The main background processes, which arise from W+jets and ${\mathrm{t\bar{t}}}$+jets in a final state with exactly one lepton and multiple jets, is reduced significantly by requiring a large azimuthal angle between the direction of the lepton and of the reconstructed W boson, computed under the hypothesis that all of the missing transverse momentum in the event arises from a neutrino produced in the leptonic decay of the W boson. The event yields observed in data are in agreement with the standard model background, which is estimated using control regions in data and corrections based on simulation. The lack of any significant excess of events is interpreted in terms of limits on the parameters of two simplified models that describe gluino pair production. For the T1tttt simplified model, in which each gluino decays to a $\mathrm{t\bar{t}}$ pair and the lightest neutralino, gluino masses up to 1.8 TeV are excluded for neutralino masses below 800 GeV. Neutralino masses below 1.1 TeV are excluded for a gluino mass up to 1.7 TeV. This result extends the exclusion limit from the previous analysis [13] on gluino masses by about 250 GeV. The second simplified model, T5qqqqWW, also describes gluino pair production, but with decays to first- or second-generation quarks and a chargino, which decays to a W boson and the lightest neutralino. The chargino mass in this decay channel is assumed to be $m_{\tilde{\chi}^{\pm}_1}=0.5(m_{{\mathrm{\widetilde{g}}}}+m_{\tilde{\chi}^0_1})$. Gluino masses below 1.9 TeV are excluded for neutralino masses below 300 GeV. This corresponds to an improvement of about 500 GeV over the previous result [13]. For a gluino mass of 1.2 TeV, neutralinos with masses up to 950 GeV are excluded. |
| Additional Figures | |
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Additional Figure 1:
Observed significance in the multi-b search regions for T1tttt. |
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Additional Figure 2:
Observed significance in the 0-b search regions for T5qqqqWW. |
| Additional Tables | |
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Additional Table 1:
Expected event yields for the four SUSY signal benchmark points defined in the text, for a total integrated luminosity of 36 fb$^{-1}$. The baseline selection corresponds to all requirements up to and including the requirement on ${L_\mathrm {T}}$. The last two lines are exclusive for the zero-b and the multi-b selection respectively. The numbers of events are corrected with scale factors to account for differences between the simulation and data for the lepton identification and isolation efficiencies, the trigger efficiency and the b-tagging efficiency. |
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