Catalog · Collider RS · CR014

CR014 $pp \to t \bar{t} t \bar{t}$

Standard-Model and BSM four-top-quark production

Status REVIEWED VERIFIED High Code: NO Priority Low

PDG / equivalent values

Observable	Value	Year	Experiment / source	Provenance
Top-philic vector mediator mass excluded in pp $ \to $ ttbar Zprime, Zprime $ \to $ ttbar, four-top two-lepton search, $\Gamma/m$ = 50%	m(Zprime) excluded up to 850 GeV (observed) 95% CL (mass_excluded_up_to)	2026	CMS	source ↑
$\sigma(pp \to $ t $\bar{t}$ t $\bar{t}$), ATLAS multilepton observation, sqrt(s)=13 TeV	$22.5^{+6.6}_{-5.5} fb$	2023	ATLAS	source ↑
$\sigma(pp \to $ t $\bar{t}$ t $\bar{t}$), CMS same-sign/multilepton observation, sqrt(s)=13 TeV	$17.7^{+4.4}_{-4.0} fb$	2023	CMS	source ↑
$\sigma(pp \to $ ttbar Zprime or t Zprime associated production, Zprime $ \to $ ttbar) times branching ratio in ATLAS top-philic simplified models	observed 95% CL upper-limit range 21-119 fb 95% CL (upper_limit_range)	2024	ATLAS	source ↑

Why this constrains the RS scan

Four-top production is relevant to custodial or composite RS because the top quark is typically the most IR-localized Standard-Model fermion. A KK gluon, composite vector, or heavy top partner can couple preferentially to tops and produce $t\bar t t\bar t$ through associated production $pp\to t\bar t X$, $X\to t\bar t$, through off-shell exchange, or through the low-energy four-top contact operators used in EFT reinterpretations. The observable therefore probes the same top-compositeness sector that direct $t\bar t$ resonance and vector-like-quark searches probe, but it does so in a more model-dependent topology. The RS scan is already dominated by low-energy quark flavor. The methodology note reports the corrected RS-anarchy median bound $M_{\rm KK}^{\min}(p50,g_s^\star=3)=47.26\,\mathrm{TeV}$. That scale is far above the present four-top resonance reach, which is sub-TeV for the broad top-philic vector benchmark in CMS-B2G-25-005 and at the few-TeV level only as a model-dependent cross-section search. Consequently CR014 is a PRIMARY collider-RS cross-check and a useful handle on aligned, custodial, or non-anarchic spectra, but it is not the leading bound for the anarchic low-energy flavor scan.

What's changed since the original paper

CMS opened the published LHC search history with the 8 TeV lepton-plus-jets analysis in arXiv:1409.7339. The importance of that result is historical: it established the multivariate strategy for a final state with a very small SM rate and large $t\bar t+$jets backgrounds. The first 13 TeV CMS searches, arXiv:1702.06164 and arXiv:1710.10614, moved the program into Run 2 and separated the lepton-plus-jets/opposite-sign dilepton and same-sign/multilepton handles. The multilepton analysis also began using four-top data to constrain the top-Higgs Yukawa coupling, making the connection to top compositeness explicit. ATLAS arXiv:1811.02305 added a 13 TeV single-lepton and opposite-sign dilepton search and combined it with earlier ATLAS multilepton inputs; CMS arXiv:1908.06463 then used the full 2016--2018 multilepton data set and added BSM scalar, pseudoscalar, and EFT interpretations. The Run-2 evidence and observation stage came from ATLAS arXiv:2106.11683, CMS arXiv:2303.03864, ATLAS arXiv:2303.15061, and CMS arXiv:2305.13439. The key changes were full Run-2 luminosity, improved heavy-flavor and lepton object identification, more powerful multivariate or graph-neural-network classifiers, and combinations across complementary final states. The direct resonance branch is now represented by ATLAS arXiv:2304.01678 and CMS-B2G-25-005/arXiv:2604.14058. These move beyond an inclusive signal-strength measurement into explicit top-philic resonance searches, but the exclusions are still benchmark dependent.

Validity and model dependence

The inclusive $t\bar t t\bar t$ cross section is a robust experimental observable, but it becomes an RS constraint only after specifying a BSM interpretation. A broad vector mediator, a scalar or pseudoscalar, a KK gluon, and a fermionic top partner can produce similar event counts but different kinematics, interference patterns, and acceptances. EFT translations are valid only when the mediator is sufficiently heavier than the resolved event scale; for lighter or broad resonances a simplified-model or full-model simulation is needed. The current top-philic resonance limits assume exclusive or dominant couplings to top quarks, specified widths, and specific production modes. A custodial-RS spectrum with several nearby resonances, non-saturated branching ratio $\mathrm{BR}(X\to t\bar t)$, additional decays to top partners, or altered top-tagging acceptance cannot be read off from the quoted mass number without a dedicated reinterpretation.

Code coverage in this repo

NO. The required CR014 grep found no implementation of four-top, top-philic-resonance, or direct collider-search constraints in quarkConstraints/, qcd/, flavorConstraints/, neutrinos/, yukawa/, warpConfig/, solvers/, scanParams/, or tests/. The exact query rg -n "CR014|four.?top|4.?top|tttt|top.?philic" ... returned no matches. A separate collider-term query found only an unrelated CMS/RunDec alpha-s test comment in tests/test\_alpha\_s.py:89. Adjacent evidence confirms that the scan computes low-energy KK-gluon flavor constraints, not collider limits. quarkConstraints/couplings.py:96 defines compute\_quark\_kk\_gluon\_couplings; quarkConstraints/deltaf2.py:449 defines evaluate\_delta\_f2\_constraints; and quarkConstraints/scan.py:377 through quarkConstraints/scan.py:441 threads those $\Delta F=2$ ratios into the quark-scan pass/fail row. No analogous module consumes LHC cross sections, resonance mass limits, or experimental likelihoods.

Implementation difficulty

HIGH. A faithful live constraint would require a model-to-collider chain: RS spectrum generation, production and decay simulation, detector-level acceptance, and a likelihood or recast for the ATLAS/CMS analyses. A simple ``$M_{\rm KK}>850\,\mathrm{GeV}$'' filter would be misleading because the CMS number is a broad top-philic vector benchmark, not a generic KK-gluon or custodial-partner exclusion. Practical implementation should use an external reinterpretation tool such as CheckMATE, MadAnalysis5, SModelS where applicable, or a preserved HEPData/analysis likelihood.

Reason: Requires collider reinterpretation, event simulation, detector acceptance, and likelihood/recast infrastructure; a direct use of the CMS 850 GeV benchmark as a generic RS M_KK bound would be incorrect.

Key references

PDG2025\_TopFourTop; ATLAS2023\_FourTopObservation; CMS2023\_FourTopObservation; CMSB2G25005\_PublicResult; CMS2026\_FourTopResonance; ATLASTopPhilic2024; CaoChenLiu2016; DeBlasEberhardtKrause2018; BanelliEtAl2021\_FourTopOperators; DarmeFuksMaltoni2021\_TopPhilic; QuarkScanMethodology2026.

display m(Zprime) excluded up to 850 GeV (observed)

AMBIGUOUS

Match 1 of 2 snapshot line 82

L79: 
L80: 
L81:  Abstract:
L82:  A search for a heavy resonance in four top quark events is presented, and interpreted in models featuring a new vector, scalar, or pseudoscalar boson which interacts exclusively with top quarks. Proton-proton collision data at centre-of-mass energies of 13.0 TeV and 13.6 TeV are analysed, corresponding to integrated luminosities of 138 fb$ ^{-1} $ and 35 fb$ ^{-1} $, respectively. Events with two leptons (electrons or muons) and jets are selected. The mass of the heavy resonance is reconstructed from a pair of jets that are formed using a variable-radius jet clustering algorithm. A machine learning approach is used to identify if these jets originate from top quarks that decay fully hadronically. The dominant background from misidentified jets is estimated from data as a function of the invariant dijet mass. Upper limits are set on the resonance production cross section for resonance masses between 500 GeV and 4 TeV and relative widths ranging from 4 to 50%. Resonances with 50% relative width are excluded at 95% confidence level up to masses of 850 GeV, with an expected exclusion limit of 1000 GeV.
L83: 
L84: 
L85:

Match 2 of 2 snapshot line 726

L723: 
L724: 
L725: 
L726:  A search for a heavy resonance is presented, examining models where a new boson interacts exclusively with top quarks, resulting in events comprising four top quarks. Two proton-proton collision data sets are analysed corresponding to 138 fb$ ^{-1} $ and 35 fb$ ^{-1} $ for centre-of-mass energies of 13 and 13.6 TeV, respectively. The mass of the new boson is reconstructed from a pair of variable-radius jets with a boosted decision tree used for identification of hadronically decaying top quarks. The additional top quarks are assumed to decay each into a b quark, a lepton (electron or muon), and a neutrino, resulting in a signature with two leptons, two b quark jets, and two large-radius jets. Contributions from background processes are estimated using a data-driven approach. Exclusion limits on the production cross section are determined for boson masses between 500 GeV and 4 TeV and relative decay widths ranging between 4 and 50% of the mediator mass. The analysis is sensitive to scalar, pseudoscalar, or vector bosons decaying to $ \mathrm{t} \overline{\mathrm{t}} $, and further interpretations are provided in the context of extended Higgs sectors and models with axion-like particles. For the 50% width hypothesis, vector mediators with masses up to 850 GeV are excluded (1000 GeV expected). The largest deviation from the background hypothesis for the vector scenario has a local significance of 2.2 standard deviations, with similar results for the scalar and pseudoscalar mediators. The obtained upper limits are the first results from the CMS collaboration for this signature that incorporates a proton-proton collision data set at 13.6 TeV and the first dedicated search of this type in the two-lepton channel.
L727: 
L728: 
L729:

display observed 95% CL upper-limit range 21-119 fb

RESOLVED

Match snapshot line 16

L13:     <updated>2024-04-16T09:58:42Z</updated>
L14:     <link href="https://arxiv.org/abs/2304.01678v2" rel="alternate" type="text/html"/>
L15:     <link href="https://arxiv.org/pdf/2304.01678v2" rel="related" type="application/pdf" title="pdf"/>
L16:     <summary>A search for the associated production of a heavy resonance with a top-quark or a top-antitop-quark pair, and decaying into a $t\bar{t}$ pair is presented. The search uses the data recorded by the ATLAS detector in $pp$ collisions at $\sqrt{s}= 13$ TeV at the Large Hadron Collider during the years 2015-2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. Events containing exactly one electron or muon are selected. The two hadronically decaying top quarks from the resonance decay are reconstructed using jets clustered with a large radius parameter of $R=1$. The invariant mass spectrum of the two top quark candidates is used to search for a resonance signal in the range of 1.0 TeV to 3.2 TeV. The presence of a signal is examined using an approach with minimal model dependence followed by a model-dependent interpretation. No significant excess is observed over the background expectation. Upper limits on the production cross section times branching ratio at 95% confidence level are provided for a heavy $Z^\prime$ boson based on a simplified model, for $Z^\prime$ mass between 1.0 TeV and 3.0 TeV. The observed (expected) limits range from 21 (14) fb to 119 (86) fb depending on the choice of model parameters.</summary>
L17:     <category term="hep-ex" scheme="http://arxiv.org/schemas/atom"/>
L18:     <published>2023-04-04T10:07:13Z</published>
L19:     <arxiv:comment>47 pages in total, author list starting page 30, 9 figures, 1 table. All figures including auxiliary figures will be available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2022-14/</arxiv:comment>