CMS-PAS-TOP-18-003

CMS-PAS-TOP-18-003
Search for standard model production of four top quarks in final states with same-sign and multiple leptons in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
March 2019

Abstract: The standard model (SM) production of four top quarks ( $\mathrm{t\overline{t}t\overline{t}}$ ) is studied by the CMS Collaboration using proton-proton collision events collected in Run 2 of the CERN LHC, with a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 137 fb $^{-1}$ . The events are required to contain a pair of same-sign leptons ( $e, \mu$ ) or at least three leptons, and several jets. Two approaches are used to enhance signal sensitivity: first a simple classification based on the number of jets and b-tagged jets, and second a boosted decision tree (BDT) taking advantage of kinematic variables related to leptons and jets. Control regions are used to constrain the dominant SM backgrounds. The two approaches find consistent results compatible with next-to-leading-order SM predictions. The observed (expected) significance of the BDT analysis is 2.6 (2.7) standard deviations, and the $\mathrm{t\overline{t}t\overline{t}}$ cross section is measured to be 12.6 $^{+5.8}_{-5.2}$ fb. These results are used to constrain the Yukawa coupling of the top quark, $y_{\rm{t}}$ , yielding a 95% confidence level limit of $\|y_{\rm{t}}/y_{\rm{t}}^{\rm{SM}}\| <$ 1.7, where $y_{\rm{t}}^{\rm{SM}}$ is the SM value of $y_{\rm{t}}$ . Limits are also set on the production of a heavy scalar or pseudoscalar in a type II 2HDM scenario, with exclusions in the mass ranges of 350-470 GeV and 350-550 GeV for heavy scalar and pseudoscalar bosons, respectively, for the 2HDM scenarios considered.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, EPJC 80 (2020) 75. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distributions in ${N_\text {jets}}$ (upper left), ${N_\text {b}}$ (upper right), ${H_{\mathrm {T}}}$ (lower left), and ${p_{\mathrm {T}}^{\text {miss}}}$ (lower right) in the signal regions summed (SR 1-14), before fitting to data, where the last bins include the overflows. The hatched areas represent the total uncertainties in the SM signal and background predictions. The ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal assumes the SM cross section from Ref. [1]. The lower panels show the ratios of the observed event yield to the total prediction. Bins without a data point have no observed events.
png pdf	Figure 1-a: Distributions in ${N_\text {jets}}$ (upper left), ${N_\text {b}}$ (upper right), ${H_{\mathrm {T}}}$ (lower left), and ${p_{\mathrm {T}}^{\text {miss}}}$ (lower right) in the signal regions summed (SR 1-14), before fitting to data, where the last bins include the overflows. The hatched areas represent the total uncertainties in the SM signal and background predictions. The ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal assumes the SM cross section from Ref. [1]. The lower panels show the ratios of the observed event yield to the total prediction. Bins without a data point have no observed events.
png pdf	Figure 1-b: Distributions in ${N_\text {jets}}$ (upper left), ${N_\text {b}}$ (upper right), ${H_{\mathrm {T}}}$ (lower left), and ${p_{\mathrm {T}}^{\text {miss}}}$ (lower right) in the signal regions summed (SR 1-14), before fitting to data, where the last bins include the overflows. The hatched areas represent the total uncertainties in the SM signal and background predictions. The ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal assumes the SM cross section from Ref. [1]. The lower panels show the ratios of the observed event yield to the total prediction. Bins without a data point have no observed events.
png pdf	Figure 1-c: Distributions in ${N_\text {jets}}$ (upper left), ${N_\text {b}}$ (upper right), ${H_{\mathrm {T}}}$ (lower left), and ${p_{\mathrm {T}}^{\text {miss}}}$ (lower right) in the signal regions summed (SR 1-14), before fitting to data, where the last bins include the overflows. The hatched areas represent the total uncertainties in the SM signal and background predictions. The ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal assumes the SM cross section from Ref. [1]. The lower panels show the ratios of the observed event yield to the total prediction. Bins without a data point have no observed events.
png pdf	Figure 1-d: Distributions in ${N_\text {jets}}$ (upper left), ${N_\text {b}}$ (upper right), ${H_{\mathrm {T}}}$ (lower left), and ${p_{\mathrm {T}}^{\text {miss}}}$ (lower right) in the signal regions summed (SR 1-14), before fitting to data, where the last bins include the overflows. The hatched areas represent the total uncertainties in the SM signal and background predictions. The ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal assumes the SM cross section from Ref. [1]. The lower panels show the ratios of the observed event yield to the total prediction. Bins without a data point have no observed events.
png pdf	Figure 2: Distributions in ${N_\text {jets}}$ and ${N_\text {b}}$ in ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{W}}$ (upper) and ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{Z}}$ (lower) control regions, before fitting to data. The hatched area represents the uncertainty in the SM background prediction, while the solid line represents the overlaid ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal, assuming the SM cross section from Ref. [27]. The lower panels show the ratios of the observed event yield to the total background prediction. Bins without a data point have no observed events.
png pdf	Figure 2-a: Distributions in ${N_\text {jets}}$ and ${N_\text {b}}$ in ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{W}}$ (upper) and ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{Z}}$ (lower) control regions, before fitting to data. The hatched area represents the uncertainty in the SM background prediction, while the solid line represents the overlaid ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal, assuming the SM cross section from Ref. [27]. The lower panels show the ratios of the observed event yield to the total background prediction. Bins without a data point have no observed events.
png pdf	Figure 2-b: Distributions in ${N_\text {jets}}$ and ${N_\text {b}}$ in ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{W}}$ (upper) and ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{Z}}$ (lower) control regions, before fitting to data. The hatched area represents the uncertainty in the SM background prediction, while the solid line represents the overlaid ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal, assuming the SM cross section from Ref. [27]. The lower panels show the ratios of the observed event yield to the total background prediction. Bins without a data point have no observed events.
png pdf	Figure 2-c: Distributions in ${N_\text {jets}}$ and ${N_\text {b}}$ in ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{W}}$ (upper) and ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{Z}}$ (lower) control regions, before fitting to data. The hatched area represents the uncertainty in the SM background prediction, while the solid line represents the overlaid ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal, assuming the SM cross section from Ref. [27]. The lower panels show the ratios of the observed event yield to the total background prediction. Bins without a data point have no observed events.
png pdf	Figure 2-d: Distributions in ${N_\text {jets}}$ and ${N_\text {b}}$ in ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{W}}$ (upper) and ${{\mathrm{t} \mathrm{\bar{t}}} \mathrm{Z}}$ (lower) control regions, before fitting to data. The hatched area represents the uncertainty in the SM background prediction, while the solid line represents the overlaid ${{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}}$ signal, assuming the SM cross section from Ref. [27]. The lower panels show the ratios of the observed event yield to the total background prediction. Bins without a data point have no observed events.
png pdf	Figure 3: Observed yields in the control and signal regions for the cut-based (left) and BDT (right) analyses, compared to the post-fit predictions for signal and background processes. The hatched areas represent the total post-fit uncertainties in the signal and background predictions. The lower panels show the ratios of the observed event yield and the total prediction of signal and background.
png pdf	Figure 3-a: Observed yields in the control and signal regions for the cut-based (left) and BDT (right) analyses, compared to the post-fit predictions for signal and background processes. The hatched areas represent the total post-fit uncertainties in the signal and background predictions. The lower panels show the ratios of the observed event yield and the total prediction of signal and background.
png pdf	Figure 3-b: Observed yields in the control and signal regions for the cut-based (left) and BDT (right) analyses, compared to the post-fit predictions for signal and background processes. The hatched areas represent the total post-fit uncertainties in the signal and background predictions. The lower panels show the ratios of the observed event yield and the total prediction of signal and background.
png pdf	Figure 4: The predicted SM value of ${\sigma ({\mathrm{p}} {\mathrm{p}} \rightarrow {{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}})}$ [2], calculated at LO and scaled to the 12.0 $^{+2.2}_{-2.5}$ fb cross section obtained in Ref. [1], as a function of $\|y_{\rm {t}}/y_{\rm {t}}^{\rm {SM}}\|$ (dashed line), compared with the observed value of ${\sigma ({\mathrm{p}} {\mathrm{p}} \rightarrow {{\mathrm{t} \mathrm{\bar{t}}} {\mathrm{t} \mathrm{\bar{t}}}})}$ (solid line), and with the observed 95% CL upper limit (hatched line).
png pdf	Figure 5: Cross section limits, as a function of boson mass, for heavy scalar (left) and pseudoscalar (right) bosons, produced in association with one or two top quarks. The bosons subsequently decay to top quark pairs. The theoretical cross sections are shown with solid red lines.
png pdf	Figure 5-a: Cross section limits, as a function of boson mass, for heavy scalar (left) and pseudoscalar (right) bosons, produced in association with one or two top quarks. The bosons subsequently decay to top quark pairs. The theoretical cross sections are shown with solid red lines.
png pdf	Figure 5-b: Cross section limits, as a function of boson mass, for heavy scalar (left) and pseudoscalar (right) bosons, produced in association with one or two top quarks. The bosons subsequently decay to top quark pairs. The theoretical cross sections are shown with solid red lines.

Tables
png pdf	Table 1: Definition of the 14 SRs and two CRs, CRW and CRZ, for the full Run2 cut-based analysis.
png pdf	Table 2: Summary of the sources of uncertainty and their effect on signal and background yields. The first group lists experimental and theoretical uncertainties in simulated signal and background processes. The second group lists normalization uncertainties in the estimated backgrounds. Uncertainties marked with a $\dagger$ in the first column are treated as fully correlated across the three years.
png pdf	Table 3: The post-fit background, signal, and total yields with their total uncertainties and the observed number of events in the control and signal regions in data for the cut-based analysis.
png pdf	Table 4: The post-fit background, signal, and total yields with their total uncertainties and the observed number of events in the control and signal regions in data for the BDT analysis.

Summary

The standard model (SM) production of

${\mathrm{t\bar{t}}\mathrm{t\bar{t}}}$ has been studied using data from

$\sqrt{s} =$ 13 TeV proton-proton collisions collected with the CMS detector during Run 2 of the LHC (2016-2018), corresponding to an integrated luminosity of 137 fb

$^{-1}$ . The final state with two same-sign leptons or at least three leptons is analyzed with two strategies, the first relying on a cut-based categorization in lepton and jet multiplicity and jet flavor, the second taking advantage of a multivariate approach to distinguish the

${\mathrm{t\bar{t}}\mathrm{t\bar{t}}}$ from its many backgrounds. The multivariate strategy yields an observed (expected) significance of 2.6 (2.7) standard deviations relative to the background-only hypothesis, and a measured value for the

${\mathrm{t\bar{t}}\mathrm{t\bar{t}}}$ cross section of 12.6

$^{+5.8}_{-5.2}$ fb, in agreement with the standard model prediction of 12.0

$^{+2.2}_{-2.5}$ fb [1]. The cut-based strategy yields an observed (expected) significance of 1.7 (2.5) standard deviations relative to the background-only hypothesis, and a measured value for the

${\mathrm{t\bar{t}}\mathrm{t\bar{t}}}$ cross section of 9.4

$^{+6.2}_{-5.6}$ fb, in agreement with the BDT result. The results of the BDT analysis are also used to constrain the top quark Yukawa coupling with respect to its SM value, based on the

$|y_{\rm{t}}|$ dependence of

${\sigma({\mathrm{p}}{\mathrm{p}}\rightarrow{\mathrm{t\bar{t}}\mathrm{t\bar{t}}} )}$ calculated at leading order in Ref. [2], resulting in a 95% confidence level limit of

$|y_{\rm{t}}/y_{\rm{t}}^{\rm{SM}}| <$ 1.7. Additionally, in Type II two-Higgs-double models, the analysis provides exclusions in the mass ranges of 350-470 GeV and 350-550 GeV for heavy scalar and pseudoscalar bosons, respectively.

References
1	R. Frederix, D. Pagani, and M. Zaro	Large NLO corrections in $t\bar{t}W^{\pm}$ and $t\bar{t}t\bar{t}$ hadroproduction from supposedly subleading EW contributions	JHEP 02 (2018) 031	1711.02116
2	Q.-H. Cao, S.-L. Chen, and Y. Liu	Probing Higgs width and top quark Yukawa coupling from ${\rm t\bar{t}H}$ and ${\rm t\bar{t}t\bar{t}}$ productions	PRD 95 (2017) 053004	1602.01934
3	Q.-H. Cao et al.	Limiting Top-Higgs Interaction and Higgs-Boson Width from Multi-Top Productions		1901.04567
4	D. Dicus, A. Stange, and S. Willenbrock	Higgs decay to top quarks at hadron colliders	PLB 333 (1994) 126	hep-ph/9404359
5	N. Craig et al.	The hunt for the rest of the Higgs bosons	JHEP 06 (2015) 137	1504.04630
6	N. Craig et al.	Heavy Higgs bosons at low $\tan \beta$ : from the LHC to 100 TeV	JHEP 01 (2017) 018	1605.08744
7	E. Alvarez et al.	Four Tops for LHC	NPB915 (2017) 19--43	1611.05032
8	N. P. Hartland et al.	A Monte Carlo global analysis of the Standard Model Effective Field Theory: the top quark sector		1901.05965
9	P. Ramond	Dual theory for free fermions	PRD 3 (1971) 2415
10	Y. A. Gol'fand and E. P. Likhtman	Extension of the algebra of Poincar $\'e$ group generators and violation of P invariance	JEPTL 13 (1971)323
11	A. Neveu and J. H. Schwarz	Factorizable dual model of pions	NPB 31 (1971) 86
12	D. V. Volkov and V. P. Akulov	Possible universal neutrino interaction	JEPTL 16 (1972)438
13	J. Wess and B. Zumino	A lagrangian model invariant under supergauge transformations	PLB 49 (1974) 52
14	J. Wess and B. Zumino	Supergauge transformations in four-dimensions	NPB 70 (1974) 39
15	P. Fayet	Supergauge invariant extension of the Higgs mechanism and a model for the electron and its neutrino	NPB 90 (1975) 104
16	H. P. Nilles	Supersymmetry, supergravity and particle physics	PR 110 (1984) 1
17	S. P. Martin	A supersymmetry primer	in Perspectives on Supersymmetry II, G. L. Kane, ed., p. 1 World Scientific, 2010 Adv. Ser. Direct. High Energy Phys., vol. 21
18	G. R. Farrar and P. Fayet	Phenomenology of the production, decay, and detection of new hadronic states associated with supersymmetry	PLB 76 (1978) 575
19	T. Plehn and T. M. P. Tait	Seeking sgluons	JPG 36 (2009) 075001	0810.3919
20	S. Calvet, B. Fuks, P. Gris, and L. Valery	Searching for sgluons in multitop events at a center-of-mass energy of 8 TeV	JHEP 04 (2013) 043	1212.3360
21	Particle Data Group, C. Patrignani et al.	Review of Particle Physics	CPC 40 (2016) 100001
22	CMS Collaboration	Search for standard model production of four top quarks in proton-proton collisions at $\sqrt{s} =$ 13 TeV	PLB 772 (2017) 336	CMS-TOP-16-016 1702.06164
23	ATLAS Collaboration	Search for new phenomena in events with same-charge leptons and $b$ -jets in $pp$ collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector	JHEP 12 (2018) 039	1807.11883
24	ATLAS Collaboration	Search for four-top-quark production in the single-lepton and opposite-sign dilepton final states in pp collisions at $\sqrt{s} =$ 13 TeV with the ATLAS detector	Submitted to: PR(2018)	1811.02305
25	CMS Collaboration	Search for physics beyond the standard model in events with two leptons of same sign, missing transverse momentum, and jets in proton-proton collisions at $\sqrt{s}=$ 13 TeV	EPJC 77 (2017) 578	CMS-SUS-16-035 1704.07323
26	CMS Collaboration	Search for standard model production of four top quarks with same-sign and multilepton final states in proton-proton collisions at $\sqrt{s} =$ 13 TeV	EPJC78 (2018), no. 2, 140	CMS-TOP-17-009 1710.10614
27	J. Alwall et al.	The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations	JHEP 07 (2014) 079	1405.0301
28	T. Melia, P. Nason, R. Rontsch, and G. Zanderighi	W $^+$ W $^-$ , WZ and ZZ production in the POWHEG BOX	JHEP 11 (2011) 078	1107.5051
29	P. Nason and G. Zanderighi	$\mathrm{W}^+ \mathrm{W}^-$ , $\mathrm{W} \mathrm{Z}$ and $\mathrm{Z} \mathrm{Z}$ production in the POWHEG BOX V2	EPJC 74 (2014) 2702	1311.1365
30	D. de Florian et al.	Handbook of LHC Higgs cross sections: 4. deciphering the nature of the Higgs sector	CERN-2017-002-M	1610.07922
31	P. S. Bhupal Dev and A. Pilaftsis	Maximally Symmetric Two Higgs Doublet Model with Natural Standard Model Alignment	JHEP 12 (2014) 024	1408.3405
32	NNPDF Collaboration	Parton distributions for the LHC Run II	JHEP 04 (2015) 040	1410.8849
33	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC77 (2017), no. 10, 663	1706.00428
34	T. Sjostrand, S. Mrenna, and P. Z. Skands	A brief introduction to PYTHIA 8.1	CPC 178 (2008) 852	0710.3820
35	J. Alwall et al.	Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions	EPJC 53 (2008) 473	0706.2569
36	R. Frederix and S. Frixione	Merging meets matching in MC@NLO	JHEP 12 (2012) 061	1209.6215
37	GEANT4 Collaboration	$GEANT4\$ --- $\$ a simulation toolkit	NIMA 506 (2003) 250
38	CMS Collaboration	Measurements of $t\bar{t}$ 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	PLB776 (2018) 355--378	CMS-TOP-16-010 1705.10141
39	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
40	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
41	CMS Collaboration	Particle-flow reconstruction and global event description with the cms detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
42	CMS Collaboration	Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $\sqrt{s} =$ 8 TeV	JINST 10 (2015) P06005	CMS-EGM-13-001 1502.02701
43	CMS Collaboration	Performance of CMS muon reconstruction in pp collision events at $\sqrt{s}=$ 7 TeV	JINST 7 (2012) P10002	CMS-MUO-10-004 1206.4071
44	M. Cacciari, G. P. Salam, and G. Soyez	The anti- $k_t$ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
45	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
46	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
47	CMS Collaboration	Jet algorithms performance in 13 TeV data	CMS-PAS-JME-16-003	CMS-PAS-JME-16-003
48	CMS Collaboration	Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV	JINST 13 (2018), no. 05, P05011	CMS-BTV-16-002 1712.07158
49	CMS Collaboration	Performance of missing transverse momentum in pp collisions at sqrt(s)=13 TeV using the CMS detector	CMS-PAS-JME-17-001	CMS-PAS-JME-17-001
50	CMS Collaboration	Search for new physics in same-sign dilepton events in proton-proton collisions at $\sqrt{s} =$ 13 TeV	EPJC 76 (2016) 439	CMS-SUS-15-008 1605.03171
51	CMS Collaboration	CMS Technical Design Report for the Pixel Detector Upgrade	CDS
52	CMS Collaboration	CMS luminosity measurements for the 2016 data taking period	CMS-PAS-LUM-17-001	CMS-PAS-LUM-17-001
53	CMS Collaboration	Measurement of the inelastic proton-proton cross section at $\sqrt{s}=$ 13 TeV	JHEP 07 (2018) 161	CMS-FSQ-15-005 1802.02613
54	CMS Collaboration	Observation of $\mathrm{t\overline{t}}$ H production	PRL 120 (2018), no. 23, 231801	CMS-HIG-17-035 1804.02610
55	ATLAS and CMS Collaborations	Procedure for the LHC Higgs boson search combination in summer 2011	ATL-PHYS-PUB-2011-011, CMS NOTE-2011/005
56	ATLAS Collaboration	Measurement of the $t\bar{t}Z$ and $t\bar{t}W$ cross sections in proton-proton collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector		1901.03584
57	CMS Collaboration	Measurement of the cross section for top quark pair production in association with a W or Z boson in proton-proton collisions at $\sqrt{s} =$ 13 TeV	JHEP 08 (2018) 011	CMS-TOP-17-005 1711.02547
58	ATLAS Collaboration	Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector	PLB784 (2018) 173--191	1806.00425
59	CMS Collaboration	Precise determination of the mass of the Higgs boson and tests of compatibility of its couplings with the standard model predictions using proton collisions at 7 and 8 TeV	EPJC 75 (2015) 212	CMS-HIG-14-009 1412.8662
60	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
61	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
62	A. L. Read	Presentation of search results: the $CL_s$ technique	in Durham IPPP Workshop: Advanced Statistical Techniques in Particle Physics, p. 2693 Durham, UK, March, 2002 JPG 28 (2002) 2693