CMS-PAS-B2G-23-010

CMS-PAS-B2G-23-010
Search for heavy resonances decaying to a top quark-antiquark pair in dilepton + jets final states
CMS Collaboration
2025-11-04

Abstract: A search for a heavy resonance decaying into a top quark and antiquark pair is performed using proton-proton collisions at $ \sqrt{s}= $ 13 TeV. The search uses the dataset collected with the CMS detector during Run 2, corresponding to total integrated luminosity of 138 fb$^{-1}$. The analysis considers final states where both top quarks decay leptonically. Events are selected by requiring two charged leptons, missing transverse momentum and jet activity. Jets containing b-hadrons are required in order to reduce the background from standard model processes. The analysis is optimized for events where the top quarks are Lorentz-boosted resulting in collimated decay products. To achieve improved sensitivity for the signal detection, kinematic variables carrying information about large momentum transfer are examined for local excesses above the background expectation. No significant deviations from the standard model predictions are found. Exclusion limits are set on the production cross section times branching ratio for hypothetical Z' boson, Kaluza-Klein gluon, and dark matter mediator particle Z'$_{\mathrm{DM}} $ that decay into top quark pairs.
Links: CDS record (PDF) ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distributions of $ \Delta R_{\text{sum}} $ in $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (bottom) events before the fit to data. The contributions from two representative signal hypotheses are shown, each normalized to a cross section of 10 pb.
png pdf	Figure 1-a: Distributions of $ \Delta R_{\text{sum}} $ in $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (bottom) events before the fit to data. The contributions from two representative signal hypotheses are shown, each normalized to a cross section of 10 pb.
png pdf	Figure 1-b: Distributions of $ \Delta R_{\text{sum}} $ in $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (bottom) events before the fit to data. The contributions from two representative signal hypotheses are shown, each normalized to a cross section of 10 pb.
png pdf	Figure 1-c: Distributions of $ \Delta R_{\text{sum}} $ in $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (bottom) events before the fit to data. The contributions from two representative signal hypotheses are shown, each normalized to a cross section of 10 pb.
png pdf	Figure 2: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the background-enriched CR for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. Background uncertainty bands are also shown.
png pdf	Figure 2-a: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the background-enriched CR for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. Background uncertainty bands are also shown.
png pdf	Figure 2-b: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the background-enriched CR for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. Background uncertainty bands are also shown.
png pdf	Figure 2-c: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the background-enriched CR for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. Background uncertainty bands are also shown.
png pdf	Figure 3: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the resolved signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 3-a: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the resolved signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 3-b: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the resolved signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 3-c: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the resolved signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 4: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the boosted signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 4-a: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the boosted signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 4-b: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the boosted signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 4-c: Post-fit distributions of $ S_{\mathrm{T}} $ variable in the boosted signal region for $ \mu\mu $ (upper left), $ \mathrm{e}\mu $ (upper right), and $ \mathrm{e}\mathrm{e} $ (lower) events. The expected contributions from a 2 TeV narrow-width Z' boson and a 4.5 TeV $ g_{\mathrm{KK}} $ resonance are overlaid, together with the background uncertainty bands.
png pdf	Figure 5: Observed and expected limits on cross section times $ \mathrm{t} \overline{\mathrm{t}} $ branching fraction at 95% CL for each of the five signal hypotheses considered in this analysis. Bands at 1 and 2 standard deviations are also shown for expected limits.
png pdf	Figure 5-a: Observed and expected limits on cross section times $ \mathrm{t} \overline{\mathrm{t}} $ branching fraction at 95% CL for each of the five signal hypotheses considered in this analysis. Bands at 1 and 2 standard deviations are also shown for expected limits.
png pdf	Figure 5-b: Observed and expected limits on cross section times $ \mathrm{t} \overline{\mathrm{t}} $ branching fraction at 95% CL for each of the five signal hypotheses considered in this analysis. Bands at 1 and 2 standard deviations are also shown for expected limits.
png pdf	Figure 5-c: Observed and expected limits on cross section times $ \mathrm{t} \overline{\mathrm{t}} $ branching fraction at 95% CL for each of the five signal hypotheses considered in this analysis. Bands at 1 and 2 standard deviations are also shown for expected limits.
png pdf	Figure 5-d: Observed and expected limits on cross section times $ \mathrm{t} \overline{\mathrm{t}} $ branching fraction at 95% CL for each of the five signal hypotheses considered in this analysis. Bands at 1 and 2 standard deviations are also shown for expected limits.
png pdf	Figure 5-e: Observed and expected limits on cross section times $ \mathrm{t} \overline{\mathrm{t}} $ branching fraction at 95% CL for each of the five signal hypotheses considered in this analysis. Bands at 1 and 2 standard deviations are also shown for expected limits.

Summary

A search for a generic massive top quark-antiquark resonance has been presented using data collected by the CMS experiment during 2016-2018 at $ \sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The analysis targets $ \mathrm{t} \overline{\mathrm{t}} $ resonances in the dileptonic decay channel, where the top quarks are highly boosted and their decay products are often collimated. The observed data are consistent with the background-only hypothesis, and no evidence for a massive $ \mathrm{t} \overline{\mathrm{t}} $ resonance is found. Upper limits at 95% confidence level are set on the production cross section of spin-1 resonances decaying to $ \mathrm{t} \overline{\mathrm{t}} $ pairs, for a range of decay widths. A topcolor Z' boson with relative widths of 1, 10, and 30% is excluded in the mass ranges 1.0-2.0, 1.0-4.7, and 1.0-5.7 TeV, respectively. The Kaluza-Klein excitation of the gluon in the Randall-Sundrum scenario ($ g_{\mathrm{KK}} $) is excluded in the mass range 1.0-3.5 TeV. The dark matter mediator Z'$_{\mathrm{DM}} $, predicted in simplified DM models, is excluded in the mass range 1.0-1.5 TeV, marking the first Z'$_{\mathrm{DM}} $ search in the dileptonic $ \mathrm{t} \overline{\mathrm{t}} $ channel in CMS. Compared with previous results at $ \sqrt{s} = $ 8 and 13 TeV, these limits provide the most stringent constraints to date in this channel. They extend the observed (expected) Z' exclusions to 2.0 (2.3), 4.7 (4.2), and 5.7 (5.0) TeV for 1%, 10%, and 30% widths, respectively, the $ g_{\mathrm{KK}} $ exclusion to 3.5 (3.1) TeV, and the Z'$_{\mathrm{DM}} $ exclusion to 1.5 (2) TeV, offering complementary coverage to the lepton-plus-jets and all-hadronic final states.

References
1	J. L. Rosner	Prominent decay modes of a leptophobic Z'	PLB 387 (1996) 113	hep-ph/9607207
2	K. R. Lynch et al.	Finding Z-prime bosons coupled preferentially to the third family at LEP and the Tevatron	PRD 63 (2001) 035006	hep-ph/0007286
3	M. S. Carena et al.	Z$ ^\prime $ gauge bosons at the Tevatron	PRD 70 (2004) 093009	hep-ph/0408098
4	C. T. Hill	Topcolor: Top quark condensation in a gauge extension of the standard model	PLB 266 (1991) 419
5	R. M. Harris and S. Jain	Cross Sections for Leptophobic Topcolor Z' decaying to top-antitop	EPJC 72 (2012) 2072
6	C. T. Hill and S. J. Parke	Top production: Sensitivity to new physics	PRD 49 (1994) 4454	hep-ph/9312324
7	C. T. Hill	Topcolor assisted technicolor	PLB 345 (1995) 483	hep-ph/9411426
8	P. H. Frampton and S. L. Glashow	Chiral color: An alternative to the standard model	PLB 190 (1987) 157
9	D. Choudhury et al.	Top production at the Tevatron/LHC and nonstandard, strongly interacting spin one particles	Update in 0810.3635 PLB 657 (2007) 69	0705.1499
10	D. Dicus, A. Stange, and S. Willenbrock	Higgs decay to top quarks at hadron colliders	PLB 333 (1994) 126	hep-ph/9404359
11	K. Agashe et al.	LHC Signals from Warped Extra Dimensions	PRD 77 (2008) 015003	hep-ph/0612015
12	H. Davoudiasl, J. L. Hewett, and T. G. Rizzo	Phenomenology of the randall-sundrum gauge hierarchy model	PRL 84 (2000) 2080
13	L. Randall and R. Sundrum	Large mass hierarchy from a small extra dimension	PRL 83 (1999) 3370
14	A. Albert et al.	Recommendations of the LHC Dark Matter Working Group: Comparing LHC searches for heavy mediators of dark matter production in visible and invisible decay channels	link
15	D. Abercrombie et al.	Dark Matter benchmark models for early LHC Run-2 Searches: Report of the ATLAS/CMS Dark Matter Forum	Physics of the Dark Universe 27 (2020) 100371
16	ATLAS Collaboration	Search for heavy particles decaying into top-quark-pairs using lepton-plus-jets events in proton-proton collisions at $ \sqrt{s} = $ 13 TeV with the ATLAS detector	EPJC 78 (2018) 565	1804.10823
17	CMS Collaboration	Search for resonant $ {\mathrm{t}\overline{\mathrm{t}}} $ production in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	JHEP 19 (2019) 031	1810.05905
18	ATLAS Collaboration	Search for $ t\overline{t} $ resonances in fully hadronic final states in $ pp $ collisions at $ \sqrt{s} = $ 13 TeV with the ATLAS detector	JHEP 10 (2020) 061	2005.05138
19	R. M. Harris and S. Jain	Cross Sections for Leptophobic Topcolor Z' Decaying to Top-Antitop	EPJC 72 (2012) 2072	1112.4928
20	S. Ask et al.	Identifying the colour of TeV-scale resonances	JHEP 2012 (2012)
21	B. Lillie, L. Randall, and L.-T. Wang	The bulk RS KK-gluon at the LHC	JHEP 2007 (2007) 074--074
22	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004
23	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
24	CMS Collaboration	Performance of the CMS Level-1 trigger in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	JINST 15 (2020) P10017	CMS-TRG-17-001 2006.10165
25	A. Hayrapetyan, A. Tumasyan, W. Adam et al.	Performance of the cms high-level trigger during lhc run 2	JINST 19 (2024) P11021
26	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
27	CMS Collaboration	Description and performance of track and primary-vertex reconstruction with the CMS tracker	JINST 9 (2014) P10009	CMS-TRK-11-001 1405.6569
28	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ k_{\mathrm{T}} $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
29	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
30	CMS Collaboration	Performance of the CMS muon detector and muon reconstruction with proton--proton collisions at $ \sqrt{s}= $ 13 TeV	JINST 13 (2018) P06015	CMS-MUO-16-001 1804.04528
31	CMS Collaboration	Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC	JINST 16 (2021) P05014	CMS-EGM-17-001 2012.06888
32	M. Cacciari, G. P. Salam, and G. Soyez	The catchment area of jets	JHEP 04 (2008) 005	0802.1188
33	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV	JINST 12 (2017) P02014	CMS-JME-13-004 1607.03663
34	CMS Collaboration	Pileup mitigation at CMS in 13 TeV data	JINST 15 (2020) P09018	CMS-JME-18-001 2003.00503
35	CMS Collaboration	Identification of heavy-flavour jets with the cms detector in pp collisions at 13 TeV	Journal of Instrumentation, 2018 link
36	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 2014 (2014) 79
37	T. Sjostrand et al.	An introduction to PYTHIA 8.2	Computer Physics Communications 191 (2015) 159--177
38	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
39	M. L. Mangano, M. Moretti, F. Piccinini, and M. Treccani	Matching matrix elements and shower evolution for top-quark production in hadronic collisions	JHEP 01 (2007) 013	hep-ph/0611129
40	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663
41	CMS Collaboration	Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements	The European Physical Journal C 4, 2020 link
42	GEANT4 Collaboration	GEANT4---a simulation toolkit	NIM A 506 (2003) 250
43	A. Hayrapetyan, A. Tumasyan, W. Adam et al.	The cms statistical analysis and combination tool: Combine	Computing and Software for Big Science 8 (2024)
44	CMS Collaboration	Precision luminosity measurement in proton-proton collisions at $ \sqrt{s}= $ 13 TeV in 2015 and 2016 at CMS	EPJC 81 (2021) 800	CMS-LUM-17-003 2104.01927
45	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $ \sqrt{s}= $ 13 TeV	CMS Physics Analysis Summary, 2018 CMS-PAS-LUM-17-004	CMS-PAS-LUM-17-004
46	CMS Collaboration	CMS luminosity measurement for the 2018 data-taking period at $ \sqrt{s}= $ 13 TeV	CMS Physics Analysis Summary, 2019 CMS-PAS-LUM-18-002	CMS-PAS-LUM-18-002
47	CMS Collaboration	Measurement of the inelastic proton-proton cross section at $ \sqrt{s} = $ 13 TeV	JHEP 2018 (2018) 161	CMS-FSQ-15-005 1802.02613
48	CMS Collaboration	Measurement of differential cross sections for top quark pair production using the lepton+jets final state in proton-proton collisions at 13 TeV	PRD 95 (2017) 092001	CMS-TOP-16-008 1610.04191
49	J. Butterworth et al.	PDF4LHC recommendations for LHC run II	JPG 43 (2016) 023001	1510.03865
50	W. Eadie et al.	Statistical Methods in Experimental Physics	vol. 6, North Holland, --80, 1971 Amsterdam 7 (1971) 9
51	F. James	Statistical Methods in Experimental Physics	2nd ed., World Scientific, --87, 2006 Singapore 8 (2006) 3
52	T. Junk	Confidence level computation for combining searches with small statistics	NIM A 434 (1999) 435	hep-ex/9902006
53	A. L. Read	Presentation of search results: The $ \text{CL}_\text{s} $ technique	JPG 28 (2002) 2693
54	ATLAS and CMS Collaborations, and the LHC Higgs Combination Group	Procedure for the LHC Higgs boson search combination in Summer 2011	Technical Report CMS-NOTE-2011-005, ATL-PHYS-PUB-2011-11, 2011
55	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727