CMS-PAS-TOP-16-016

CMS-PAS-TOP-16-016
Search for standard model production of four top quarks in proton-proton collisions at 13 TeV
CMS Collaboration
August 2016

Abstract: A search for standard model four top quark production, combining the single lepton and dilepton channels, is presented. The analysis utilises the data recorded by the CMS experiment at $\sqrt{s} =$ 13 TeV in 2015, which corresponds to an integrated luminosity of 2.6 fb $^{-1}$ . A boosted decision tree algorithm is used to select signal and suppress background events. Upper limits on four top quark production of $10.2 \times \sigma_{t\overline{t}t\overline{t}}^{SM}$ observed and $10.8^{+6.7}_{-3.8} \times \sigma_{t\overline{t}t\overline{t}}^{SM}$ expected are calculated at the 95% confidence level.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 772 (2017) 336. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The dominant diagram for ${\mathrm {t}\overline {\mathrm {t}}} {\mathrm {t}\overline {\mathrm {t}}}$ production in the SM at leading order.
png pdf	Figure 2-a: The ${\textrm {BDT}_{\textrm {trijet1}}}$ discriminant for data and simulation in the dilepton channel for the $\mu \mu$ (a), $\mu$ e (b) and ee (c) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 2-b: The ${\textrm {BDT}_{\textrm {trijet1}}}$ discriminant for data and simulation in the dilepton channel for the $\mu \mu$ (a), $\mu$ e (b) and ee (c) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 2-c: The ${\textrm {BDT}_{\textrm {trijet1}}}$ discriminant for data and simulation in the dilepton channel for the $\mu \mu$ (a), $\mu$ e (b) and ee (c) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 3-a: The ${\textrm {BDT}_{\textrm {trijet2}}}$ discriminant for data and simulation in the single lepton channel for the $\mu$ +jets (a) and e+jets (b) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 3-b: The ${\textrm {BDT}_{\textrm {trijet2}}}$ discriminant for data and simulation in the single lepton channel for the $\mu$ +jets (a) and e+jets (b) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 4-a: The $N {_{\textrm {j}}}$ distributions for data and simulation in the single lepton channel for the $\mu$ +jets (a), e+jets (b), the dilepton channel for the $\mu \mu$ (c), $\mu$ e (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 4-b: The $N {_{\textrm {j}}}$ distributions for data and simulation in the single lepton channel for the $\mu$ +jets (a), e+jets (b), the dilepton channel for the $\mu \mu$ (c), $\mu$ e (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 4-c: The $N {_{\textrm {j}}}$ distributions for data and simulation in the single lepton channel for the $\mu$ +jets (a), e+jets (b), the dilepton channel for the $\mu \mu$ (c), $\mu$ e (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 4-d: The $N {_{\textrm {j}}}$ distributions for data and simulation in the single lepton channel for the $\mu$ +jets (a), e+jets (b), the dilepton channel for the $\mu \mu$ (c), $\mu$ e (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 4-e: The $N {_{\textrm {j}}}$ distributions for data and simulation in the single lepton channel for the $\mu$ +jets (a), e+jets (b), the dilepton channel for the $\mu \mu$ (c), $\mu$ e (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 5-a: The $S$ distributions for data and simulation in the dilepton channel for the $\mu \mu$ (a), $\mu$ e (b) and ee (bottom) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 5-b: The $S$ distributions for data and simulation in the dilepton channel for the $\mu \mu$ (a), $\mu$ e (b) and ee (bottom) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 5-c: The $S$ distributions for data and simulation in the dilepton channel for the $\mu \mu$ (a), $\mu$ e (b) and ee (bottom) final states with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 6-a: The $T$ distributions for data and simulation in the single lepton channel for the $\mu$ +jets (a) and e+jets (b) final states are shown with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 6-b: The $T$ distributions for data and simulation in the single lepton channel for the $\mu$ +jets (a) and e+jets (b) final states are shown with the dominant systematic uncertainty shown in hatched bands and the ${\mathrm {t}\overline {\mathrm {t}}}$ +X sample representing the sum of ${\mathrm {t}\overline {\mathrm {t}}}$ , ${\mathrm {t}\overline {\mathrm {t}}}$ +Z, ${\mathrm {t}\overline {\mathrm {t}}}$ +W, and ${\mathrm {t}\overline {\mathrm {t}}}$ +H production.
png pdf	Figure 7-a: Dilepton BDT output discriminator summed across lepton species channels for 4-5 jets (upper left), 6-7 jets (upper right), and $\geq$ 8 jets (bottom).
png pdf	Figure 7-b: Dilepton BDT output discriminator summed across lepton species channels for 4-5 jets (upper left), 6-7 jets (upper right), and $\geq$ 8 jets (bottom).
png pdf	Figure 7-c: Dilepton BDT output discriminator summed across lepton species channels for 4-5 jets (upper left), 6-7 jets (upper right), and $\geq$ 8 jets (bottom).
png pdf	Figure 8-a: BDT output distributions in the $\mu$ +jets channel (a) and e+jets channel (b) for the $\geq 9 N {_{\textrm {j}}}$ and $3 N {_{\textrm {tags}}^{\textrm {M}}}$ category.
png pdf	Figure 8-b: BDT output distributions in the $\mu$ +jets channel (a) and e+jets channel (b) for the $\geq 9 N {_{\textrm {j}}}$ and $3 N {_{\textrm {tags}}^{\textrm {M}}}$ category.
png pdf	Figure 9-a: BDT output distributions in the $\mu$ jets channel (a) and e+jets channel (b) for the $\geq 9 N {_{\textrm {j}}}$ and $\geq 4 N {_{\textrm {tags}}^{\textrm {M}}}$ category.
png pdf	Figure 9-b: BDT output distributions in the $\mu$ jets channel (a) and e+jets channel (b) for the $\geq 9 N {_{\textrm {j}}}$ and $\geq 4 N {_{\textrm {tags}}^{\textrm {M}}}$ category.
png pdf	Figure 10: Expected and observed upper limits on ${\sigma _{ {\mathrm {t}\overline {\mathrm {t}}} {\mathrm {t}\overline {\mathrm {t}}} }^{SM}}$ for the single lepton, dilepton, and combined analysis in multiples of ${\sigma _{ {\mathrm {t}\overline {\mathrm {t}}} {\mathrm {t}\overline {\mathrm {t}}} }^{SM}}$ .

Tables
png pdf	Table 1: Expected and observed 95% CL upper limits on the standard model four top quark production as a multiple of ${\sigma _{ {\mathrm {t}\overline {\mathrm {t}}} {\mathrm {t}\overline {\mathrm {t}}} }^{SM}}$ . The values quoted on the expected limits are the 1 $\sigma$ uncertainties.

Summary

A search for events containing four top quarks has been performed using 2.6 fb

$^{-1}$ of data recorded by the CMS experiment at

$\sqrt{s} =$ 13 TeV. The analysis focuses on a combination of the single lepton channel in the

$\mu$ +jets and e+jets final states and dilepton channel in the

$\mu \mu$ ,

$\mu$ e, and ee final states. The analysis is comprised of three stages. Firstly, a baseline selection is defined for each final state that is used to broadly select signal events while suppressing backgrounds. Secondly, an event classification scheme based on a BDT algorithm is defined, further enhancing sensitivity to four top quark production. The BDT algorithm exploits the differences in event activity, event topology, b content and t content to discriminate between signal and background. Thirdly, upper limits on four top quark production of

$10.2 \times {\sigma_{{t}\overline{{t}}} {{t}\overline{{t}}} }^{SM}$ observed and

$10.8^{+6.7}_{-3.8} \times \sigma^{SM}_{{{t}\overline{{t}}} {{t}\overline{{t}}} }$ expected are calculated at the 95% CL.

References
1	ATLAS, CDF, CMS, D0 Collaboration	First combination of Tevatron and LHC measurements of the top-quark mass		1403.4427
2	G. Cacciapaglia et al.	Composite scalars at the LHC: the Higgs, the Sextet and the Octet	JHEP 11 (2015) 201	1507.02283
3	C. Arina et al.	A comprehensive approach to dark matter studies: exploration of simplified top-philic models		1605.09242
4	M. Toharia and J. D. Wells	Gluino decays with heavier scalar superpartners	JHEP 02 (2006) 015	hep-ph/0503175
5	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
6	Q.-H. Cao, S.-L. Chen, and Y. Liu	Probing Higgs Width and Top Quark Yukawa Coupling from $\textrm{t}\bar{\textrm{t}}\textrm{H}$ and $\textrm{t}\bar{\textrm{t}}\textrm{t}\bar{\textrm{t}}$ Productions		1602.01934
7	O. Ducu, L. Heurtier, and J. Maurer	LHC signatures of a Z' mediator between dark matter and the SU(3) sector	JHEP 03 (2016) 006	1509.05615
8	G. Bevilacqua and M. Worek	Constraining BSM Physics at the LHC: Four top final states with NLO accuracy in perturbative QCD	JHEP 07 (2012) 111	1206.3064
9	CMS Collaboration	Search for standard model production of four top quarks in the lepton + jets channel in pp collisions at $\sqrt{s}$ = 8 TeV	JHEP 11 (2014) 154
10	ATLAS Collaboration	Search for supersymmetry at $\sqrt{s}$ =8 TeV in final states with jets and two same-sign leptons or three leptons with the ATLAS detector	JHEP 06 (2014) 035	1404.2500
11	CMS Collaboration	Search for new physics in same-sign dilepton events in proton-proton collisions at $\sqrt{s}$ = 13 TeV		CMS-SUS-15-008 1605.03171
12	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
13	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
14	J. Alwall et al.	MadGraph 5 : Going Beyond	JHEP 06 (2011) 128	1106.0522
15	P. Nason	A New method for combining NLO QCD with shower Monte Carlo algorithms	JHEP 11 (2004) 040	hep-ph/0409146
16	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with Parton Shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
17	S. Alioli, P. Nason, C. Oleari, and E. Re	A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX	JHEP 06 (2010) 043	1002.2581
18	S. Alioli, S.-O. Moch, and P. Uwer	Hadronic top-quark pair-production with one jet and parton showering	JHEP 1 (2012) 137
19	CMS Collaboration	Measurement of $\mathrm {t}\overline{\mathrm {t}}$ production with additional jet activity, including $\mathrm {b}$ quark jets, in the dilepton decay channel using pp collisions at $\sqrt{s} = 8\,\text {TeV}$	EPJC 76 (2016) 379	CMS-TOP-12-041 1510.03072
20	CMS Collaboration	Measurement of the differential cross section for $\mathrm{t \bar t}$ production in the dilepton final state at $\sqrt{s}=13 \mathrm{TeV}$	CMS-PAS-TOP-16-011	CMS-PAS-TOP-16-011
21	E. Re	Single-top Wt-channel production matched with parton showers using the POWHEG method	EPJC 71 (2011) 1547	1009.2450
22	T. Sj\"ostrand, S. Mrenna, and P. Skands	PYTHIA 6.4 physics and manual	JHEP 05 (2006) 026
23	T. Sj\"ostrand, S. Mrenna, and P. Skands	A brief introduction to PYTHIA 8.1	Computer Physics Communications 178 (2008) 852
24	NNPDF Collaboration	Unbiased global determination of parton distributions and their uncertainties at NNLO and at LO	Nucl. Phys. B 855 (2012) 153	1107.2652
25	GEANT4 Collaboration	GEANT4: A Simulation toolkit	NIMA 506 (2003) 250
26	CMS Collaboration	Particle-flow event reconstruction in CMS and performance for jets, taus, and $E_{\mathrm{T}}^{\text{miss}}$	CDS
27	CMS Collaboration	Commissioning of the particle-flow event reconstruction with the first LHC collisions recorded in the CMS detector	CDS
28	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
29	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
30	M. Cacciari, G. P. Salam, and G. Soyez	The anti- $k_t$ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
31	M. Cacciari, G. P. Salam, and G. Soyez	FastJet User Manual	EPJC 72 (2012) 1896	1111.6097
32	CMS Collaboration	Determination of jet energy calibration and transverse momentum resolution in CMS	JINST 6 (2011) P11002	CMS-JME-10-011 1107.4277
33	CMS Collaboration	Identification of b quark jets at the CMS Experiment in the LHC Run 2	CMS-PAS-BTV-15-001	CMS-PAS-BTV-15-001
34	L. Breiman, J. Friedman, R. A. Olshen, and C. J. Stone		Chapman and Hall/CRC
35	H. J. Friedman	Recent Advances in Predictive (Machine) Learning	Journal of Classification 23 (2006) 175
36	A. Hocker et al.	TMVA - Toolkit for Multivariate Data Analysis	PoS ACAT (2007) 040	physics/0703039
37	J. D. Bjorken and S. J. Brodsky	Statistical Model for electron-Positron Annihilation Into Hadrons	PRD 1 (1970) 1416
38	CMS Collaboration	CMS Luminosity Measurement for the 2015 Data Taking Period	CMS-PAS-LUM-15-001	CMS-PAS-LUM-15-001
39	M. Czakon, P. Fiedler, and A. Mitov	Total Top-Quark Pair-Production Cross Section at Hadron Colliders Through $O(\alpha^4_S)$	PRL 110 (2013) 252004	1303.6254
40	CMS Collaboration	Measurement of the cross section ratio $\textrm{t}\bar{\textrm{t}}\textrm{b}\bar{\textrm{b}}/\textrm{t}\bar{\textrm{t}}\textrm{j}\textrm{j}$ using dilepton final states in pp collisions at 13 TeV
41	L. Moneta et al.	The RooStats Project	PoS ACAT2010 (2010) 057	1009.1003
42	ATLAS, CMS, LHC Higgs Combination Group Collaboration	Procedure for the LHC Higgs boson search combination in Summer 2011	CMS-NOTE-2011-005
43	R. Barlow and C. Beeston	Fitting using finite Monte Carlo samples	Computer Physics Communications 77 (1993) 219