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| CMS-PAS-SUS-15-002 | ||
| Search for supersymmetry in the multijet and missing transverse momentum channel in pp collisions at 13 TeV | ||
| CMS Collaboration | ||
| December 2015 | ||
| Abstract: A search for new physics is performed based on multijet events with large missing transverse momentum produced in proton-proton collisions at $\sqrt{s}=$ 13 TeV. The data sample, corresponding to an integrated luminosity of 2.2 fb$^{-1}$, was collected with the CMS detector at Run-2 of the CERN LHC. The data are examined in search regions of jet multiplicity, bottom-quark jet multiplicity, missing transverse momentum, and the scalar sum of jet transverse momenta. The observed numbers of events in all search regions are found to be consistent with the expectations from standard model processes. Exclusion limits are presented for simplified supersymmetric models of gluino pair production. For a scenario in which both gluinos decay to a bottom quark-antiquark pair and to a stable, massless, weakly interacting, lightest neutralino, gluinos with mass below 1600 GeV are excluded. For the corresponding scenarios with a top quark-antiquark pair or with a generic quark-antiquark pair in place of the bottom quark-antiquark pair, the respective limits are 1530 and 1440 GeV. These results significantly extend the limits from LHC Run-1. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PLB 758 (2016) 152. |
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| Figures | |
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Figure 1-a:
Event diagrams for the SUSY scenarios considered in this study: the (a) T1bbbb, (b) T1tttt, and (c) T1qqqq simplified model spectra scenarios, with $\tilde{\chi}^{0}_{1} $ the lightest neutralino, taken to be weakly interacting and stable. |
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Figure 1-b:
Event diagrams for the SUSY scenarios considered in this study: the (a) T1bbbb, (b) T1tttt, and (c) T1qqqq simplified model spectra scenarios, with $\tilde{\chi}^{0}_{1} $ the lightest neutralino, taken to be weakly interacting and stable. |
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Figure 1-c:
Event diagrams for the SUSY scenarios considered in this study: the (a) T1bbbb, (b) T1tttt, and (c) T1qqqq simplified model spectra scenarios, with $\tilde{\chi}^{0}_{1} $ the lightest neutralino, taken to be weakly interacting and stable. |
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Figure 2:
Schematic illustration of the search intervals in the $ {H_{\mathrm T}^{\text {miss}}} $ versus $ {H_{\mathrm {T}}} $ plane. Each of the six $ {H_{\mathrm {T}}} $ and $ {H_{\mathrm T}^{\text {miss}}} $ intervals is examined as a function of three $ {N_{\text {jet}}} $ bins and four $ {N_{{\mathrm{b} }\text {-jet}}} $ bins for a total of 72 search regions. |
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Figure 3-a:
(a) The lost-lepton background in the 72 search regions of the analysis as predicted directly from $ mathrm{ t \bar{t} } $, single-top, and W+jets simulation (points with error bars) and as predicted by applying the lost-lepton background-determination procedure to simulated muon and electron control samples (histograms). The lower panel shows the ratio between the true and predicted yields. (b) The corresponding simulated results for the background from hadronically decaying $\tau $ leptons. For both plots, the six results within each region delineated by dashed lines correspond sequentially to the six regions of $ {H_{\mathrm {T}}} $ and $ {H_{\mathrm T}^{\text {miss}}} $ indicated in Fig. 2. |
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Figure 3-b:
(a) The lost-lepton background in the 72 search regions of the analysis as predicted directly from $ mathrm{ t \bar{t} } $, single-top, and W+jets simulation (points with error bars) and as predicted by applying the lost-lepton background-determination procedure to simulated muon and electron control samples (histograms). The lower panel shows the ratio between the true and predicted yields. (b) The corresponding simulated results for the background from hadronically decaying $\tau $ leptons. For both plots, the six results within each region delineated by dashed lines correspond sequentially to the six regions of $ {H_{\mathrm {T}}} $ and $ {H_{\mathrm T}^{\text {miss}}} $ indicated in Fig. 2. |
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Figure 4:
The $ \mathrm{Z} \to \nu \bar{\nu} $ background in the 72 search regions of the analysis as predicted directly from Z ($\rightarrow \ell ^{+} \ell ^{-} $)+jets and $ mathrm{ t \bar{t} } \mathrm{Z} $ simulation (histogram), and as predicted by applying the $ \mathrm{Z} \to \nu \bar{\nu} $ background-determination procedure to simulated event samples (points with error bars). For bins corresponding to $ {N_{{\mathrm{b} }\text {-jet}}} =$ 0, the agreement is exact by construction. The lower panel shows the ratio between the true and predicted yields; the shaded bands indicate the systematic uncertainty associated with the dependence of $\mathcal {F}$ on the kinematic parameters ($ {H_{\mathrm {T}}} $ and $ {H_{\mathrm T}^{\text {miss}}} $). The numbering of the bins is the same as in Fig. 3. |
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Figure 5:
The QCD multijet background in the 72 search regions of the analysis as predicted directly from QCD multijet simulation (points with error bars) and as predicted by applying the QCD multijet background-determination procedure to simulated event samples (histograms). The lower panel shows the ratio between the true and predicted yields. The numbering of the bins is the same as in Fig. 3. |
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Figure 6:
Observed numbers of events and corresponding SM background predictions in the 72 search regions of the analysis, with fractional differences shown in the lower panel. The hatched regions indicate the total uncertainties in the background predictions. The numbering of the bins is the same as in Fig. 3. |
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Figure 7-a:
Observed numbers of events and corresponding SM background predictions for intervals of the search-region phase space particularly sensitive to the (top left) T1tttt, (top right) T1bbbb, and (bottom) T1qqqq scenarios. The selection requirements are given in the figure legends. The hatched regions indicate the total uncertainties in the background predictions. The (unstacked) results for two example signal scenarios are shown in each instance, one with ${ {m_{\tilde{g} }} } $ much larger than $ { m_{{\tilde{\chi}^{0}_1}} } $ and the other with ${ {m_{ \tilde{\chi}^{0}_1}} } \approx {m_{\tilde{g} }} $. Note that for purposes of presentation, the four-bin scheme discussed in Section {sec:qcd} is used for the $ {H_{\mathrm T}^{\text {miss}}} $ variable. |
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Figure 7-b:
Observed numbers of events and corresponding SM background predictions for intervals of the search-region phase space particularly sensitive to the (top left) T1tttt, (top right) T1bbbb, and (bottom) T1qqqq scenarios. The selection requirements are given in the figure legends. The hatched regions indicate the total uncertainties in the background predictions. The (unstacked) results for two example signal scenarios are shown in each instance, one with ${ {m_{\tilde{g} }} } $ much larger than $ { m_{{\tilde{\chi}^{0}_1}} } $ and the other with ${ {m_{ \tilde{\chi}^{0}_1}} } \approx {m_{\tilde{g} }} $. Note that for purposes of presentation, the four-bin scheme discussed in Section {sec:qcd} is used for the $ {H_{\mathrm T}^{\text {miss}}} $ variable. |
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Figure 7-c:
Observed numbers of events and corresponding SM background predictions for intervals of the search-region phase space particularly sensitive to the (top left) T1tttt, (top right) T1bbbb, and (bottom) T1qqqq scenarios. The selection requirements are given in the figure legends. The hatched regions indicate the total uncertainties in the background predictions. The (unstacked) results for two example signal scenarios are shown in each instance, one with ${ {m_{\tilde{g} }} } $ much larger than $ { m_{{\tilde{\chi}^{0}_1}} } $ and the other with ${ {m_{ \tilde{\chi}^{0}_1}} } \approx {m_{\tilde{g} }} $. Note that for purposes of presentation, the four-bin scheme discussed in Section {sec:qcd} is used for the $ {H_{\mathrm T}^{\text {miss}}} $ variable. |
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Figure 8-a:
The 95% confidence level upper limits on the production cross sections for the (a) T1bbbb, (b) T1tttt, and (c) T1qqqq simplified model scenarios of supersymmetry, shown as a function of the gluino and LSP masses $ {m_{\tilde{g} }} $ and $ {m_{{\tilde{\chi} }^{0}_1}} $. The solid (black) curves show the observed exclusion contours assuming the NLO+NLL cross sections [41-45], with the corresponding $\pm 1$ standard deviation uncertainties [61]. The dashed (red) curves present the expected limits with $\pm 1$ standard deviation experimental uncertainties. The upper limit results are also provided in electronic form as root files: (a) T1bbbb, (b) T1tttt and (c) T1qqqq. |
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Figure 8-b:
The 95% confidence level upper limits on the production cross sections for the (a) T1bbbb, (b) T1tttt, and (c) T1qqqq simplified model scenarios of supersymmetry, shown as a function of the gluino and LSP masses $ {m_{\tilde{g} }} $ and $ {m_{{\tilde{\chi} }^{0}_1}} $. The solid (black) curves show the observed exclusion contours assuming the NLO+NLL cross sections [41-45], with the corresponding $\pm 1$ standard deviation uncertainties [61]. The dashed (red) curves present the expected limits with $\pm 1$ standard deviation experimental uncertainties. The upper limit results are also provided in electronic form as root files: (a) T1bbbb, (b) T1tttt and (c) T1qqqq. |
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Figure 8-c:
The 95% confidence level upper limits on the production cross sections for the (a) T1bbbb, (b) T1tttt, and (c) T1qqqq simplified model scenarios of supersymmetry, shown as a function of the gluino and LSP masses $ {m_{\tilde{g} }} $ and $ {m_{{\tilde{\chi} }^{0}_1}} $. The solid (black) curves show the observed exclusion contours assuming the NLO+NLL cross sections [41-45], with the corresponding $\pm 1$ standard deviation uncertainties [61]. The dashed (red) curves present the expected limits with $\pm 1$ standard deviation experimental uncertainties. The upper limit results are also provided in electronic form as root files: (a) T1bbbb, (b) T1tttt and (c) T1qqqq. |
| Auxiliary Figures | |
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Auxiliary Figure 1-a:
The distributions of observed and predicted number of events plotted as a function of one of the four search variables, integrated over each of the other three search variables. Clockwise from top-left: $ {H_{\mathrm T}^{\text {miss}}} $ distribution for all $ {H_{\mathrm {T}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {H_{\mathrm {T}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{\text {jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${H_{\mathrm {T}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{{\mathrm{b} }\text {-jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, $ {H_{\mathrm {T}}} $, and $ {N_{\text {jet}}} $. |
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Auxiliary Figure 1-b:
The distributions of observed and predicted number of events plotted as a function of one of the four search variables, integrated over each of the other three search variables. Clockwise from top-left: $ {H_{\mathrm T}^{\text {miss}}} $ distribution for all $ {H_{\mathrm {T}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {H_{\mathrm {T}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{\text {jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${H_{\mathrm {T}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{{\mathrm{b} }\text {-jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, $ {H_{\mathrm {T}}} $, and $ {N_{\text {jet}}} $. |
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Auxiliary Figure 1-c:
The distributions of observed and predicted number of events plotted as a function of one of the four search variables, integrated over each of the other three search variables. Clockwise from top-left: $ {H_{\mathrm T}^{\text {miss}}} $ distribution for all $ {H_{\mathrm {T}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {H_{\mathrm {T}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{\text {jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${H_{\mathrm {T}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{{\mathrm{b} }\text {-jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, $ {H_{\mathrm {T}}} $, and $ {N_{\text {jet}}} $. |
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Auxiliary Figure 1-d:
The distributions of observed and predicted number of events plotted as a function of one of the four search variables, integrated over each of the other three search variables. Clockwise from top-left: $ {H_{\mathrm T}^{\text {miss}}} $ distribution for all $ {H_{\mathrm {T}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {H_{\mathrm {T}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${N_{\text {jet}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{\text {jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, ${H_{\mathrm {T}}} $, and $ {N_{{\mathrm{b} }\text {-jet}}} $; $ {N_{{\mathrm{b} }\text {-jet}}} $ distribution for all $ {H_{\mathrm T}^{\text {miss}}} $, $ {H_{\mathrm {T}}} $, and $ {N_{\text {jet}}} $. |
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Auxiliary Figure 2:
Observed numbers of events and corresponding SM background predictions in the 72 search regions of the analysis after the final fit performed with the assumption of only standard model contributions. Background predictions before the final fit are also shown for comparison. The lower panel shows the pull distributions for the data and the pre-fit background estimates with respect to the post-fit background estimates. The six results within each region delineated by dashed lines correspond sequentially to the six regions of ${H_{\mathrm T}^{\text {miss}}} $ and $ {H_{\mathrm {T}}} $. |
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Auxiliary Figure 3:
The sensitivity of the analysis to different signal models as a function of the analysis binning. The upper panel shows the total predicted SM backgrounds and the expected number of signal events for six representative signal parameter points per analysis bin. The bottom panel shows the estimated expected discovery sensitivity (Q) per analysis bin. |
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Auxiliary Figure 4-a:
The Signal Efficiency times Acceptance after the baseline selection for the (clockwise from a to c) T1tttt, T1bbbb, and T1qqqq supersymmetry scenarios is shown as a function of the gluino and LSP masses $m_{\tilde{g}}$ and $m_{\tilde{\chi }_{1}^{0}}$. Additionally, the full Signal Efficiency of the baseline selection is provided in a root file. |
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Auxiliary Figure 4-b:
The Signal Efficiency times Acceptance after the baseline selection for the (clockwise from a to c) T1tttt, T1bbbb, and T1qqqq supersymmetry scenarios is shown as a function of the gluino and LSP masses $m_{\tilde{g}}$ and $m_{\tilde{\chi }_{1}^{0}}$. Additionally, the full Signal Efficiency of the baseline selection is provided in a root file. |
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Auxiliary Figure 4-c:
The Signal Efficiency times Acceptance after the baseline selection for the (clockwise from a to c) T1tttt, T1bbbb, and T1qqqq supersymmetry scenarios is shown as a function of the gluino and LSP masses $m_{\tilde{g}}$ and $m_{\tilde{\chi }_{1}^{0}}$. Additionally, the full Signal Efficiency of the baseline selection is provided in a root file. |
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Auxiliary Figure 5:
Event display showing the $\rho -\phi $ plane for event 258749:361:559467731, which has the highest observed $ {H_{\mathrm T}^{\text {miss}}} $ of all events in the search region. |
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Auxiliary Figure 6:
Event display showing the $\rho -\phi $ plane for event 258749:361:559467731 with a white background and an alternative color scheme. |
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Auxiliary Figure 7:
Another Event display for event 258749:361:559467731, showing the event in 3D Tower view mode. |
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Auxiliary Figure 8:
Another Event display for event 258749:361:559467731, showing the event in 3D Tower view mode with a light background and an alternative color scheme. |
| Auxiliary Tables | |
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Auxiliary Table 1:
Table of number of predicted events for each background and total number of observed events in each of the 72 signal bins. The predicted numbers are obtained using data-driven methods. |
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Auxiliary Table 2:
Absolute efficiencies in \% for each step of the signal selection, listed for two representative signal models and mass values. Only statistical uncertainties are shown. |
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