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CMS-SUS-19-008 ; CERN-EP-2020-001

Search for physics beyond the standard model in events with jets and two same-sign or at least three charged leptons in proton-proton collisions at $\sqrt{s}=$ 13 TeV

CMS Collaboration

27 January 2020

Eur. Phys. J. C 80 (2020) 752

Abstract: A data sample of events from proton-proton collisions with at least two jets, and two isolated same-sign or three or more charged leptons, is studied in a search for signatures of new physics phenomena. The data correspond to an integrated luminosity of 137 fb$^{-1}$ at a center-of-mass energy of 13 TeV, collected in 2016-2018 by the CMS experiment at the LHC. The search is performed using a total of 168 signal regions defined using several kinematic variables. The properties of the events are found to be consistent with the expectations from standard model processes. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos or squarks for various decay scenarios in the context of supersymmetric models conserving or violating R parity. The observed lower mass limits are as large as 2.1 TeV for gluinos and 0.9 TeV for top and bottom squarks. To facilitate reinterpretations, model-independent limits are provided in a set of simplified signal regions.

Links: e-print arXiv:2001.10086 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures
png pdf	Figure 1: Diagrams illustrating the simplified RPC SUSY models with gluino production considered in this analysis.
png pdf	Figure 2: Diagrams illustrating the simplified RPC SUSY models with squark production considered in this analysis.
png pdf	Figure 3: Diagrams illustrating the two simplified RPV SUSY models considered in this analysis.
png pdf	Figure 4: Distributions of the main analysis variables after the event selection: ${H_{\mathrm {T}}}$, ${{p_{\mathrm {T}}} ^\text {miss}}$, ${{m_{\mathrm {T}}} ^{\text {min}}}$, ${N_\text {jets}}$, ${N_{\mathrm{b}}}$, and the charge of the SS pair, where the last bin includes the overflow (where applicable). The hatched area represents the total statistical and systematic uncertainty in the background prediction. The lower panels show the ratio of the observed event yield to the background prediction. The prediction for the SUSY model T1tttt with $m_{{\mathrm{\widetilde{g}}}} = $ 1600 GeV and $m_{\tilde{\chi}^0_1} = $ 600 GeV is overlaid.
png pdf	Figure 4-a: Distribution of ${H_{\mathrm {T}}}$. The last bin includes the overflow. The hatched area represents the total statistical and systematic uncertainty in the background prediction. The lower panel shows the ratio of the observed event yield to the background prediction. The prediction for the SUSY model T1tttt with $m_{{\mathrm{\widetilde{g}}}} = $ 1600 GeV and $m_{\tilde{\chi}^0_1} = $ 600 GeV is overlaid.
png pdf	Figure 4-b: Distribution of ${{p_{\mathrm {T}}} ^\text {miss}}$. The last bin includes the overflow. The hatched area represents the total statistical and systematic uncertainty in the background prediction. The lower panel shows the ratio of the observed event yield to the background prediction. The prediction for the SUSY model T1tttt with $m_{{\mathrm{\widetilde{g}}}} = $ 1600 GeV and $m_{\tilde{\chi}^0_1} = $ 600 GeV is overlaid.
png pdf	Figure 4-c: Distribution of ${{m_{\mathrm {T}}} ^{\text {min}}}$. The last bin includes the overflow. The hatched area represents the total statistical and systematic uncertainty in the background prediction. The lower panel shows the ratio of the observed event yield to the background prediction. The prediction for the SUSY model T1tttt with $m_{{\mathrm{\widetilde{g}}}} = $ 1600 GeV and $m_{\tilde{\chi}^0_1} = $ 600 GeV is overlaid.
png pdf	Figure 4-d: Distribution of ${N_\text {jets}}$. The last bin includes the overflow. The hatched area represents the total statistical and systematic uncertainty in the background prediction. The lower panel shows the ratio of the observed event yield to the background prediction. The prediction for the SUSY model T1tttt with $m_{{\mathrm{\widetilde{g}}}} = $ 1600 GeV and $m_{\tilde{\chi}^0_1} = $ 600 GeV is overlaid.
png pdf	Figure 4-e: Distribution of ${N_{\mathrm{b}}}$. The hatched area represents the total statistical and systematic uncertainty in the background prediction. The lower panel shows the ratio of the observed event yield to the background prediction. The prediction for the SUSY model T1tttt with $m_{{\mathrm{\widetilde{g}}}} = $ 1600 GeV and $m_{\tilde{\chi}^0_1} = $ 600 GeV is overlaid.
png pdf	Figure 4-f: Distribution of the charge of the SS pair. The hatched area represents the total statistical and systematic uncertainty in the background prediction. The lower panel shows the ratio of the observed event yield to the background prediction. The prediction for the SUSY model T1tttt with $m_{{\mathrm{\widetilde{g}}}} = $ 1600 GeV and $m_{\tilde{\chi}^0_1} = $ 600 GeV is overlaid.
png pdf	Figure 5: Expected and observed SR yields for the HH, HL, LL signal categories. The hatched area represents the total statistical and systematic uncertainty in the background prediction.
png pdf	Figure 5-a: Expected and observed SR yields for the HH signal category. The hatched area represents the total statistical and systematic uncertainty in the background prediction.
png pdf	Figure 5-b: Expected and observed SR yields for the HL signal category. The hatched area represents the total statistical and systematic uncertainty in the background prediction.
png pdf	Figure 5-c: Expected and observed SR yields for the LL signal category. The hatched area represents the total statistical and systematic uncertainty in the background prediction.
png pdf	Figure 6: Expected and observed SR yields for the LM and ML signal categories. The hatched area represents the total statistical and systematic uncertainty in the background prediction.
png pdf	Figure 6-a: Expected and observed SR yields for the LM signal category. The hatched area represents the total statistical and systematic uncertainty in the background prediction.
png pdf	Figure 6-b: Expected and observed SR yields for the ML signal category. The hatched area represents the total statistical and systematic uncertainty in the background prediction.
png pdf	Figure 7: Exclusion regions at 95% CL in the $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ plane for the T1tttt (upper left) and T5ttbbWW (upper right) models, with off-shell third-generation squarks, and the T5tttt (lower left) and T5ttcc (lower right) models, with on-shell third-generation squarks. For the T5ttbbWW model, $m_{\tilde{\chi}^{\pm}_1} = m_{\tilde{\chi}^0_1} + $ 5 GeV, for the T5tttt model, $m_{\tilde{\mathrm{t}}} - m_{\tilde{\chi}^0_1} = m_{\mathrm{t}}$, and for the T5ttcc model, $m_{\tilde{\mathrm{t}}} - m_{\tilde{\chi}^0_1} = $ 20 GeV and the decay proceeds through $\tilde{\mathrm{t}} \to \mathrm{c} \tilde{\chi}^0_1 $. The right-hand side color scale indicates the excluded cross section values for a given point in the SUSY particle mass plane. The solid black curves represent the observed exclusion limits assuming the approximate-NNLO+NNLL cross sections [45,46,47,48,49,50,57] (thick line), or their variations of $ \pm $1 standard deviations (s.d.) (thin lines). The dashed red curves show the expected limits with the corresponding $ \pm $1 s.d. and $ \pm $2 s.d. uncertainties. Excluded regions are to the left and below the limit curves.
png pdf	Figure 7-a: Exclusion region at 95% CL in the $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ plane for the T1tttt model, with off-shell third-generation squarks. The right-hand side color scale indicates the excluded cross section values for a given point in the SUSY particle mass plane. The solid black curves represent the observed exclusion limits assuming the approximate-NNLO+NNLL cross sections [45,46,47,48,49,50,57] (thick line), or their variations of $ \pm $1 standard deviations (s.d.) (thin lines). The dashed red curves show the expected limits with the corresponding $ \pm $1 s.d. and $ \pm $2 s.d. uncertainties. Excluded regions are to the left and below the limit curves.
png pdf	Figure 7-b: Exclusion region at 95% CL in the $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ plane for the T5ttbbWW model, with off-shell third-generation squarks. For this model, $m_{\tilde{\chi}^{\pm}_1} = m_{\tilde{\chi}^0_1} + $ 5 GeV. The right-hand side color scale indicates the excluded cross section values for a given point in the SUSY particle mass plane. The solid black curves represent the observed exclusion limits assuming the approximate-NNLO+NNLL cross sections [45,46,47,48,49,50,57] (thick line), or their variations of $ \pm $1 standard deviations (s.d.) (thin lines). The dashed red curves show the expected limits with the corresponding $ \pm $1 s.d. and $ \pm $2 s.d. uncertainties. Excluded regions are to the left and below the limit curves.
png pdf	Figure 7-c: Exclusion region at 95% CL in the $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ plane for the T5tttt model, with on-shell third-generation squarks. For this model, $m_{\tilde{\mathrm{t}}} - m_{\tilde{\chi}^0_1} = m_{\mathrm{t}}$. The right-hand side color scale indicates the excluded cross section values for a given point in the SUSY particle mass plane. The solid black curves represent the observed exclusion limits assuming the approximate-NNLO+NNLL cross sections [45,46,47,48,49,50,57] (thick line), or their variations of $ \pm $1 standard deviations (s.d.) (thin lines). The dashed red curves show the expected limits with the corresponding $ \pm $1 s.d. and $ \pm $2 s.d. uncertainties. Excluded regions are to the left and below the limit curves.
png pdf	Figure 7-d: Exclusion region at 95% CL in the $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ plane for the T5ttcc model, with on-shell third-generation squarks. For this model, $m_{\tilde{\mathrm{t}}} - m_{\tilde{\chi}^0_1} = $ 20 GeV and the decay proceeds through $\tilde{\mathrm{t}} \to \mathrm{c} \tilde{\chi}^0_1 $. The right-hand side color scale indicates the excluded cross section values for a given point in the SUSY particle mass plane. The solid black curves represent the observed exclusion limits assuming the approximate-NNLO+NNLL cross sections [45,46,47,48,49,50,57] (thick line), or their variations of $ \pm $1 standard deviations (s.d.) (thin lines). The dashed red curves show the expected limits with the corresponding $ \pm $1 s.d. and $ \pm $2 s.d. uncertainties. Excluded regions are to the left and below the limit curves.
png pdf	Figure 8: Exclusion regions at 95% CL in the plane of $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ for the T5qqqqWZ model with $m_{\tilde{\chi}^{\pm}_1}=0.5(m_{{\mathrm{\widetilde{g}}}} + m_{\tilde{\chi}^0_1})$ (left) and with $m_{\tilde{\chi}^{\pm}_1} = m_{\tilde{\chi}^0_1} +$ 20 GeV (right). The notations are as in Fig. 7.
png pdf	Figure 8-a: Exclusion region at 95% CL in the plane of $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ for the T5qqqqWZ model with $m_{\tilde{\chi}^{\pm}_1}=0.5(m_{{\mathrm{\widetilde{g}}}} + m_{\tilde{\chi}^0_1})$. The notations are as in Fig. 7.
png pdf	Figure 8-b: Exclusion region at 95% CL in the plane of $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ for the T5qqqqWZ model with $m_{\tilde{\chi}^{\pm}_1} = m_{\tilde{\chi}^0_1} +$ 20 GeV. The notations are as in Fig. 7.
png pdf	Figure 9: Exclusion regions at 95% CL in the plane of $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ for the T5qqqqWW model with $m_{\tilde{\chi}^{\pm}_1}=0.5(m_{{\mathrm{\widetilde{g}}}} + m_{\tilde{\chi}^0_1})$ (left) and with $m_{\tilde{\chi}^{\pm}_1} = m_{\tilde{\chi}^0_1} + $ 20 GeV (right). The notations are as in Fig. 7.
png pdf	Figure 9-a: Exclusion region at 95% CL in the plane of $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ for the T5qqqqWW model with $m_{\tilde{\chi}^{\pm}_1}=0.5(m_{{\mathrm{\widetilde{g}}}} + m_{\tilde{\chi}^0_1})$. The notations are as in Fig. 7.
png pdf	Figure 9-b: Exclusion region at 95% CL in the plane of $m_{\tilde{\chi}^0_1}$ versus $m_{{\mathrm{\widetilde{g}}}}$ for the T5qqqqWW model with $m_{\tilde{\chi}^{\pm}_1} = m_{\tilde{\chi}^0_1} + $ 20 GeV. The notations are as in Fig. 7.
png pdf	Figure 10: Exclusion regions at 95% CL in the plane of $m_{\tilde{\chi}^{\pm}_1}$ versus $m_{\tilde{\mathrm{b}} _{1}}$ for the T6ttWW model with $m_{\tilde{\chi}^0_1} = $ 50 GeV. The notations are as in Fig. 7.
png pdf	Figure 11: Exclusion regions at 95% CL in the plane of $m(\tilde{\mathrm{t}} _{1})$ versus $m(\tilde{\mathrm{t}} _{2})$ for the T6ttHZ model with $m(\tilde{\mathrm{t}} _{1})-m(\tilde{\chi}^0_1) = $ 175 GeV. The three exclusions represent $\mathcal {B}(\tilde{\mathrm{t}} _{2}\to \tilde{\mathrm{t}} _{1}\mathrm{Z})$ of 0, 50, and 100%, respectively. The notations are as in Fig. 7.
png pdf	Figure 11-a: Exclusion regions at 95% CL in the plane of $m(\tilde{\mathrm{t}} _{1})$ versus $m(\tilde{\mathrm{t}} _{2})$ for the T6ttHZ model with $m(\tilde{\mathrm{t}} _{1})-m(\tilde{\chi}^0_1) = $ 175 GeV. The three exclusions represent $\mathcal {B}(\tilde{\mathrm{t}} _{2}\to \tilde{\mathrm{t}} _{1}\mathrm{Z})$ of 0%. The notations are as in Fig. 7.
png pdf	Figure 11-b: Exclusion regions at 95% CL in the plane of $m(\tilde{\mathrm{t}} _{1})$ versus $m(\tilde{\mathrm{t}} _{2})$ for the T6ttHZ model with $m(\tilde{\mathrm{t}} _{1})-m(\tilde{\chi}^0_1) = $ 175 GeV. The three exclusions represent $\mathcal {B}(\tilde{\mathrm{t}} _{2}\to \tilde{\mathrm{t}} _{1}\mathrm{Z})$ of 50%. The notations are as in Fig. 7.
png pdf	Figure 11-c: Exclusion regions at 95% CL in the plane of $m(\tilde{\mathrm{t}} _{1})$ versus $m(\tilde{\mathrm{t}} _{2})$ for the T6ttHZ model with $m(\tilde{\mathrm{t}} _{1})-m(\tilde{\chi}^0_1) = $ 175 GeV. The three exclusions represent $\mathcal {B}(\tilde{\mathrm{t}} _{2}\to \tilde{\mathrm{t}} _{1}\mathrm{Z})$ of 100%. The notations are as in Fig. 7.
png pdf	Figure 12: Upper limits at 95% CL on the cross section for RPV gluino pair production with each gluino decaying into four quarks and one lepton (T1qqqqL, left), and each gluino decaying into a top, bottom, and strange quarks (T1tbs, right).
png pdf	Figure 12-a: Upper limits at 95% CL on the cross section for RPV gluino pair production with each gluino decaying into four quarks and one lepton (T1qqqqL).
png pdf	Figure 12-b: Upper limits at 95% CL on the cross section for RPV gluino pair production with each gluino decaying into a top, bottom, and strange quarks (T1tbs).
png pdf	Figure 13: Upper limits at 95% CL on the product of cross section, detector acceptance, and selection efficiency, $\sigma \, \mathcal {A} \epsilon $, for the production of an SS lepton pair with at least two jets, as a function of the minimum ${{p_{\mathrm {T}}} ^\text {miss}}$ threshold, when $ {H_{\mathrm {T}}} > $ 300 GeV (left), or the minimum ${H_{\mathrm {T}}}$ threshold, when $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV (right).
png pdf	Figure 13-a: Upper limit at 95% CL on the product of cross section, detector acceptance, and selection efficiency, $\sigma \, \mathcal {A} \epsilon $, for the production of an SS lepton pair with at least two jets, as a function of the minimum ${{p_{\mathrm {T}}} ^\text {miss}}$ threshold, when $ {H_{\mathrm {T}}} > $ 300 GeV.
png pdf	Figure 13-b: Upper limit at 95% CL on the product of cross section, detector acceptance, and selection efficiency, $\sigma \, \mathcal {A} \epsilon $, for the production of an SS lepton pair with at least two jets, as a function of the minimum ${H_{\mathrm {T}}}$ threshold, when $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 300 GeV.

Tables
png pdf	Table 1: Transverse momentum and pseudorapidity requirements for leptons and jets. Note that the $ {p_{\mathrm {T}}} $ thresholds to count jets and b-tagged jets are different; the jet multiplicity ${N_\text {jets}}$ includes b-tagged jets if their ${p_{\mathrm {T}}}$ exceeds 40 GeV.
png pdf	Table 2: The SR definitions for the HH category. Charge-split regions are indicated with ($++$) and ($- -$). The three highest $ {H_{\mathrm {T}}} $ regions are split only by $ {N_\text {jets}} $, resulting in 62 regions in total. Quantities are specified in units of GeV where applicable.
png pdf	Table 3: The SR definitions for the HL category. Charge-split regions are indicated with ($++$) and ($- -$). There are 43 regions in total. Quantities are specified in units of GeV where applicable.
png pdf	Table 4: The SR definitions for the LL category. All SRs in this category require $ {N_\text {jets}} \geq $ 2. There are 8 regions in total. Quantities are specified in units of GeV where applicable.
png pdf	Table 5: The SR definitions for the LM category. All SRs in this category require $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV and $ {H_{\mathrm {T}}} > $ 300 GeV. The two high-$ {H_{\mathrm {T}}} $ regions are split only by $ {N_\text {jets}} $, resulting in 11 regions in total. Quantities are specified in units of GeV where applicable.
png pdf	Table 6: The SR definitions for the ML category. All SRs in these categories require $ {N_\text {jets}} \geq $ 2. Regions marked with ${}^\dagger $ are split by $ {{m_{\mathrm {T}}} ^{\text {min}}} = $ 120 GeV, with the high-$ {{m_{\mathrm {T}}} ^{\text {min}}} $ region specified by the second SR label. On-Z regions events include an OS same-flavor pair with 76 $ < m_{\ell \ell} < $ 106 GeV. There are 44 regions in total. Quantities are specified in units of GeV where applicable.
png pdf	Table 7: Summary of the sources of systematic uncertainty and their effect on the yields of different processes in the SRs. The first two groups list experimental and theoretical uncertainties assigned to processes estimated using simulation, while the last group lists uncertainties assigned to processes whose yield is estimated from the data. The uncertainties in the first group also apply to signal samples. Reported values are representative for the most relevant signal regions.
png pdf	Table 8: Expected background event yields, total uncertainties, and observed event yields in the SRs used in this search.
png pdf	Table 9: Inclusive SR definitions, expected background yields and uncertainties, and observed yields, as well as the observed 95% CL upper limits on the number of BSM events contributing to each region. No uncertainty in the signal acceptance is assumed in calculating these limits. A dash ($- -$) indicates that a particular selection is not required.

Summary

A sample of events with two same-sign or at least three charged leptons produced in association with several jets in proton-proton collisions at 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$, has been studied to search for manifestations of physics beyond the standard model. The data are found to be consistent with the standard model expectations. The results are interpreted as limits on cross sections at 95% confidence level for the production of new particles in simplified supersymmetric models, considering both R parity conserving and violating scenarios. Using calculations for these cross sections as functions of particle masses, the limits are translated into lower mass limits that are as large as 2.1 TeV for gluinos and 0.9 TeV for top and bottom squarks, depending on the details of the model. The results extend the gluino and squark mass observed and expected exclusions by up to 200 GeV, compared to the previous versions of this analysis. Finally, to facilitate further interpretations of the search, model-independent limits are provided as a function of the missing transverse momentum and the scalar sum of jet transverse momenta in an event, together with the background prediction and data yields in a set of simplified signal regions.

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65	M. Cacciari and G. P. Salam	Pileup subtraction using jet areas	PLB 659 (2008) 119	0707.1378
66	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV	JINST 12 (2016) P02014	CMS-JME-13-004 1607.03663
67	CMS Collaboration	Jet algorithms performance in 13 TeV data	CMS-PAS-JME-16-003	CMS-PAS-JME-16-003
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76	A. Kalogeropoulos and J. Alwall	The SysCalc code: A tool to derive theoretical systematic uncertainties		1801.08401
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79	CMS Collaboration	Measurements of $ {\rm t\bar{t}} $ cross sections in association with b jets and inclusive jets and their ratio using dilepton final states in pp collisions at $ \sqrt{s} = $ 13 TeV	PLB 776 (2018) 355	CMS-TOP-16-010 1705.10141
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