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CMS-PAS-SUS-16-042

Search for supersymmetry in events with one lepton and multiple jets in proton-proton collisions at $\sqrt{s}= $ 13 TeV with 2016 data

CMS Collaboration

March 2017

Abstract: A search for supersymmetry is performed with proton-proton collision data recorded by the CMS experiment with a center-of-mass energy of 13 TeV and an integrated luminosity of 35.9 fb$^{-1}$. Data containing a single lepton are sorted into several exclusive search regions based on the number of jets and $b$-tagged jets, the scalar sum of the jet transverse momenta, and the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. The observed number of events are consistent with the background expectation and the results are interpreted with two simplified supersymmetric models of gluino pair production. In the first model, each gluino decays via a three-body process to top quarks and a neutralino, which is associated with the observed missing transverse momentum in the event. Gluinos with masses up to 1.8 TeV are excluded for neutralino masses below 800 GeV. In the second model, each gluino decays via a three-body process to two light quarks and a chargino, which subsequently decays to a W boson and a neutralino. The mass of the chargino is taken to be midway between the gluino and neutralino masses. In this model, gluinos with masses below 1.9 TeV are excluded for neutralino masses below 300 GeV.

Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 780 (2018) 384. The superseded preliminary plots can be found here.

Additional information on efficiencies needed for reinterpretation of these results are available here. Additional technical material for CMS speakers can be found here

Figures
png pdf	Figure 1: Diagrams showing the simplified models (left) T1tttt and (right) T5qqqqWW. Depending on the mass difference between the chargino ($\tilde{\chi}^{\pm}_1$) and the neutralino ($\tilde{\chi}^0_1$), the W boson can be virtual.
png pdf	Figure 1-a: Diagram showing the simplified model T1tttt.
png pdf	Figure 1-b: Diagram showing the simplified model T5qqqqWW. Depending on the mass difference between the chargino ($\tilde{\chi}^{\pm}_1$) and the neutralino ($\tilde{\chi}^0_1$), the W boson can be virtual.
png pdf	Figure 2: Multi-b search: comparison of the number of events observed in the data and the numbers expected from the estimated SM backgrounds in the 39 search bins defined in the text. Upper panel: the data are shown by black points with error bars, while the total SM background expected is shown as a grey line with a hatched region that represents the uncertainty. For illustration, the relative fraction of the different SM background contributions, as determined from simulation, is shown by the stacked, colored histograms, which are 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 shown by open histograms. Lower panel: the ratio of the number of events observed in data to the number of events expected from the SM background, for each search bin. The error bars on the data points indicate the combined statistical and systematic uncertainty in the ratio. The grey hatched region indicates the uncertainty on the ratio that arises from the uncertainty on the background estimate.
png pdf	Figure 3: Zero-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. Upper panel: the data are shown by black points with error bars, while the total SM background expected is shown as a grey line with a hatched region that represents the uncertainty. The filled, stacked histograms represent the predictions for $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $+jets, W+jets events, and the remaining backgrounds. The expected yields from two T5qqqqWW model points are shown as solid lines. lower panel: the ratio of the number of events observed in data to the number of events expected from the SM background, for each search bin. the error bars on the data points indicate the combined statistical and systematic uncertainty in the ratio. the grey hatched region indicates the uncertainty on the ratio that arises from the uncertainty on the background estimate.
png pdf	Figure 4: Cross section limits at a 95% CL for the (left) T1tttt and (right) T5qqqqWW models, as a function of the gluino and LSP masses. In T5qqqqWW, the pair-produced gluinos decay to a first- or second-generation quark-antiquark pair ($ {\mathrm{ q } \mathrm{ \bar{q} } }$) and a chargino ($\tilde{\chi}^{\pm}_1$) with its mass taken to be $m_{\tilde{\chi}^{\pm}_1 }=0.5(m_{\tilde{ \mathrm{g} } }+m_{\tilde{\chi}^0_1 })$. 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 ${\pm }$1$\sigma $ uncertainty bands related to the theoretical (experimental) uncertainties.
png pdf root	Figure 4-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 ${\pm }$1$\sigma $ uncertainty bands related to the theoretical (experimental) uncertainties.
png pdf root	Figure 4-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 a first- or second-generation quark-antiquark pair ($ {\mathrm{ q } \mathrm{ \bar{q} } }$) and a chargino ($\tilde{\chi}^{\pm}_1$) with its mass taken to be $m_{\tilde{\chi}^{\pm}_1 }=0.5(m_{\tilde{ \mathrm{g} } }+m_{\tilde{\chi}^0_1 })$. 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 ${\pm }$1$\sigma $ uncertainty bands related to the theoretical (experimental) uncertainties.

Tables
png pdf	Table 1: Overview of the definitions of sideband and mainband regions. For the multijet (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. Empty cells are not used in the analysis.
png pdf	Table 2: Summary of systematic uncertainties in the total background estimates for the multi-b and for the zero-b analyses.
png pdf	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 zero-b analyses, are usually larger for compressed scenarios, where the mass difference between the gluino and the lightest neutralino is small.
png pdf	Table 4: Number of expected background events and the measured number of events in the aggregated signal regions.
png pdf	Table 5: Search regions and the corresponding minimum ${\Delta \Phi }$ requirements.
png pdf	Table 6: Summary of the results in the multi-b search.
png pdf	Table 7: Results table of the 0-tag regions, 36fb$^{-1}$.

Summary

A search for supersymmetry has been performed with 36 fb$^{-1}$ of proton-proton collision data recorded by the CMS experiment at $ \sqrt{s} = $ 13 TeV in 2016. Several exclusive search bins, differing 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, which arises from W+jets and $ \mathrm{ t \bar{t} }$+jets events, is reduced significantly by requiring a large azimuthal angle between the directions of the momenta of the lepton and of the reconstructed W boson, attributing all the $ E_{\mathrm{T}}^{\text{miss}} $ in the event to a neutrino from the leptonic decay of a W boson. The data observed are in agreement with the estimate of the standard model background, which is based on data samples 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 model, in which each gluino decays through an off-shell top squark 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 can be excluded for a gluino mass up to 1.7 TeV. The second simplified model, T5qqqqWW, also contains gluino pair production, with the gluinos decaying to first- or second-generation squarks and a chargino, which subsequently decays to a W boson and the lightest neutralino. The chargino mass in this decay chain is taken to be $m_{\tilde{\chi}^{\pm}_1} = 0.5 (m_{\tilde{ \mathrm{g} }}+m_{\tilde{\chi}^0_1})$. In this model, gluino masses below 1.9 TeV are excluded for neutralino masses below 300 GeV. For a gluino mass of 1.2 TeV, neutralinos with masses up to 950 GeV can be excluded.

Additional Figures
png pdf	Additional Figure 1: Observed significance in the multi-b search regions for T1tttt.
png pdf	Additional Figure 2: Observed significance in the 0-b search regions for T5qqqqWW.

Additional Tables

png pdf

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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