CR001 $pp \to g_{KK}^{(1)} \to t \bar{t}$
KK-gluon resonance in $t-\bar{t}$ Status REVIEWED VERIFIED High Code: NO Priority High
PDG / equivalent values
| Observable | Value | Year | Experiment / source | Provenance |
|---|---|---|---|---|
| Excluded RS KK-gluon mass interval in pp $ \to g_{KK} \to $ t $\bar{t}$ | 0.5 < m(g_KK) < 5.5 TeV excluded 95% CL (95% CL mass exclusion interval upper edge; interpreted as lower bound above the excluded interval for this benchmark) | 2026 | CMS | source ↑ |
| Excluded RS KK-gluon mass interval in pp $ \to g_{KK} \to $ t $\bar{t}$ | 0.50 < m(g_KK) < 4.55 TeV excluded 95% CL (historical 95% CL mass exclusion interval upper edge) | 2019 | CMS | source ↑ |
| PDG Live S071KKG RS KK-gluon mass lower bound | m(g_KK) > 3.8 TeV 95% CL (review-table lower limit) | 2026 | ATLAS | source ↑ |
| Excluded RS KK-gluon masses in ATLAS 7 TeV lepton+jets search | m(g_KK) < 2.07 TeV excluded 95% credibility level (historical 95% credibility-level mass exclusion) | 2013 | ATLAS | source ↑ |
| Excluded RS KK-gluon masses in ATLAS boosted 7 TeV lepton+jets search | m(g_KK) < 1.5 TeV excluded 95% credibility level (historical 95% credibility-level mass exclusion) | 2012 | ATLAS | source ↑ |
Why this constrains the RS scan
The search constrains the physical first KK-gluon resonance mass in a specified
RS collider benchmark: production through the color-octet vector state,
template assumptions for its width and couplings, and a large branching
fraction to \(t\bar t\). This is the canonical collider signature of bulk RS
because the IR-localized top quark couples strongly to the KK gluon.
For the anarchic-flavor scan in this repository, the direct reach is not the
leading mass constraint. The methodology note's RUNA reference scan gives
\(\MKKmin(p50,\gsstar=3)=47.26\) TeV and
\(\MKKmin(p95,\gsstar=3)=127.13\) TeV from low-energy \(\Delta F=2\) flavor
constraints. A \(5.5\) TeV direct \(g_{\rm KK}\to t\bar t\) exclusion is
therefore mainly a cross-check for the anarchic pipeline and a useful handle on
non-anarchic, aligned, or otherwise collider-visible RS variants where the
flavor bound is weakened.
What's changed since the original paper
The collider history starts from the Lillie--Randall--Wang boosted-top
proposal, arXiv:2005.05138 brought the all-hadronic channel to the
\(139\,{\rm fb}^{-1}\) Run-2 scale, while ATLAS
hep-ph/0701166, which identified \(g_{\rm KK}\to t\bar t\)
as the characteristic bulk-RS LHC signal. Post-2010 searches improved by
raising the collision energy, adding luminosity, and extending top-tagging
across boosted decay topologies.
ATLAS arXiv:1207.2409 used \(2.05\,{\rm fb}^{-1}\) at 7 TeV and
excluded \(m_{g_{\rm KK}}<1.5\) TeV, establishing the boosted lepton-plus-jets
strategy. ATLAS arXiv:1305.2756 used the full 2011
\(4.7\,{\rm fb}^{-1}\) 7 TeV sample and pushed the broad RS KK-gluon exclusion
to \(m_{g_{\rm KK}}<2.07\) TeV. Early 13 TeV CMS work,
arXiv:1704.03366, combined boosted lepton-plus-jets and fully
hadronic channels and improved sensitivity above 2 TeV.
ATLAS arXiv:1804.10823 used \(36.1\,{\rm fb}^{-1}\) at 13 TeV in the
lepton-plus-jets channel; this is the ATLAS result behind the PDG Live
\(3.8\) TeV benchmark row. CMS arXiv:1810.05905 then combined the
dilepton, single-lepton, and all-hadronic \(t\bar t\) topologies in
\(35.9\,{\rm fb}^{-1}\), excluding \(0.50arXiv:2512.17856
updated one- and two-lepton final states with \(140\,{\rm fb}^{-1}\) and
explicit KK-gluon templates over a \(0.4\)--\(5.0\) TeV search range. CMS
arXiv:2603.23454 is the current full-Run-2 all-topology update and
sets the \(5.5\) TeV limit used here.Validity and model dependence
The limit is not a model-independent lower bound on every RS \(M_{\rm KK}\).
It assumes the signal model used by the experimental template: the KK-gluon
production rate, width, chiral couplings, and \(t\bar t\) branching fraction.
If the KK gluon has sizable decays to vector-like quarks, other BSM states, or
light-flavor channels, the \(t\bar t\) branching fraction and line shape change.
Very broad resonances, interference with SM \(t\bar t\), or altered light-quark
couplings also require reinterpretation rather than direct use of the quoted
mass edge.
For custodial RS, this entry constrains the KK gauge resonance sector. It does
not by itself constrain custodial fermion partners such as \(T_{5/3}\); those
require separate heavy-partner searches and branching assumptions.
Code coverage in this repo
NO for a direct-collider \(g_{\rm KK}\to t\bar t\) constraint. The
direct-search grep over
quarkConstraints/, qcd/,
flavorConstraints/, neutrinos/, yukawa/,
warpConfig/, solvers/, scanParams/, and
tests/ found no ttbar, top-pair-resonance, LHC, CheckMATE,
MadAnalysis5, or SModelS implementation.
There is adjacent low-energy KK-gluon infrastructure only:
quarkConstraints/couplings.py:1 defines mass-basis KK-gluon couplings,
quarkConstraints/deltaf2.py:1 describes a tree-level KK-gluon-inspired
\(\Delta F=2\) matching layer, and quarkConstraints/scan.py:359-380
computes \(M_{\rm KK}\) and evaluates flavor diagnostics. The modern matching
wrapper also states that it is not a full operator-complete EFT/RG package
(quarkConstraints/modern/matching.py:241-243). None of these files
implements a collider likelihood or filters scan points on direct LHC
resonance exclusions.Implementation difficulty
HIGH. A live constraint would need either the experimental likelihood
or an external reinterpretation chain such as CheckMATE, MadAnalysis5, SModelS,
or a dedicated recast using generated \(pp\to g_{\rm KK}\to t\bar t\) samples,
top-tagging efficiencies, mass-resolution effects, and width/interference
systematics. A simple mass cut would be acceptable only as a documented
benchmark overlay, not as a robust constraint on the general RS parameter
space.
Reason: Requires external collider-recast machinery or collaboration likelihoods, including signal generation, top-tagging efficiencies, acceptance, resolution, width and interference dependence, and benchmark-specific branching assumptions.
Key references
CMS2026\_TTbarResonance; HEPData2026\_CMSB2G25009;
PDGLive2026\_S071KKG; CMS2019\_TTbarResonance;
ATLAS2025\_TTbarResonance; ATLAS2020\_HadronicTTbar;
ATLAS2018\_LeptonJetsTTbar; ATLAS2013\_LeptonJetsTTbar;
ATLAS2012\_BoostedTTbar; CMS2017\_BoostedTTbar;
LillieRandallWang2007\_BulkRSKKGluon;
QuarkScanMethodology2026\_MKK.