CR003 $pp \to T \bar{T} \to tZ/tH/bW + X$
Pair production of custodial charge-2/3 top partner T (T') Status REVIEWED VERIFIED High Code: NO Priority Medium
PDG / equivalent values
| Observable | Value | Year | Experiment / source | Provenance |
|---|---|---|---|---|
| Pair-produced vector-like charge-2/3 T mass lower limit, B(T $ \to $ Wb) = 1 | m_T > 1.70 TeV 95% CL (lower_mass_exclusion) | 2024 | ATLAS | source ↑ |
| Pair-produced vector-like charge-2/3 T mass lower limit, isospin-singlet branching pattern | $m_T > 1.36 TeV for B(T \to Wb:Ht:Zt) = 1/2:1/4:1/4$ 95% CL (lower_mass_exclusion) | 2024 | ATLAS | source ↑ |
| Pair-produced vector-like charge-2/3 T mass lower limit, B(T $ \to $ Zt) = 1 | m_T > 1.60 TeV 95% CL (lower_mass_exclusion) | 2023 | ATLAS | source ↑ |
| Pair-produced vector-like charge-2/3 T mass lower limit, B(T $ \to $ Ht) = 1 | m_T > 1.50 TeV 95% CL (lower_mass_exclusion) | 2023 | CMS | source ↑ |
| Pair-produced vector-like charge-2/3 T mass lower limit for all Wb/Zt/Ht decay mixtures to third-generation quarks | m_T > 1.48 TeV for all decays to third-generation quarks 95% CL (lower_mass_exclusion) | 2023 | CMS | source ↑ |
Why this constrains the RS scan
CR003 constrains the physical mass of a charge-\(2/3\) custodial fermion
partner, not the KK-gluon mass or the flavor-anarchy matching scale by itself.
For QCD pair production the production rate is comparatively model-independent,
but the acceptance and mass limit depend on the assumed branching fractions
among \(Wb\), \(Zt\), and \(Ht\). A custodial-RS model can map the lightest
top-partner mass and branching ratios to the 5D fermion representation, IR
localization, and electroweak embedding; absent that map, the LHC number is a
direct-search cross-check rather than a universal RS-flavor bound.
The current low-energy quark-flavor scan already quotes
\(M_{KK}^{\min}(p50,g_\ast=3)=47.26~\mathrm{TeV}\) in
docs/quark\_scan\_methodology\_note.tex. The \(T\)-partner direct
limits above sit in the \(1.36\)--\(1.70~\mathrm{TeV}\) range, so they do not
compete with the anarchic-flavor \(M_{KK}\) envelope. Their value is instead
to test non-anarchic corners, spectra with light custodial fermions, or models
where collider partners are not tied tightly to the flavor-setting KK scale.What's changed since the original paper
The Contino--Servant top-partner paper set the custodial-partner collider
motivation before LHC data. The LHC search history then moved from early
same-sign and lepton+jets top-partner searches to full-Run-2
branching-fraction scans. ATLAS arXiv:1707.03347 established a 13 TeV
lepton+jets \(Wb\)-targeted search with boosted \(W\) reconstruction. ATLAS
arXiv:1803.09678 and arXiv:1808.01771 broadened the coverage to \(Ht\),
\(Zt\), multi-\(b\), and all-hadronic final states. ATLAS arXiv:2210.15413
used the full Run-2 \(Z\)-lepton channel and gives the strongest pure-\(Zt\)
row in the PDG table. CMS arXiv:2209.07327 combined single-lepton,
same-sign dilepton, and multilepton channels and gives the robust
all-decay-mixture exclusion. ATLAS arXiv:2401.17165 is the current
PDG-leading pure-\(Wb\) and singlet \(Wb:Ht:Zt\) source.
Validity and model dependence
These limits assume prompt pair production of narrow vector-like quarks and
specific decay-mode hypotheses. The common simplified-model assumption is
that \({\cal B}(T\to Wb)+{\cal B}(T\to Zt)+{\cal B}(T\to Ht)=1\). Exotic
decays, sizable widths, altered electroweak couplings, long-lived partners, or
compressed spectra can invalidate a direct reading of the quoted mass limits.
Single-production searches can reach higher masses for chosen couplings, but
they are not the CR003 observable because the assigned process is pair
production.
Code coverage in this repo
NO. Targeted greps across
quarkConstraints/, qcd/,
flavorConstraints/, neutrinos/, yukawa/,
warpConfig/, solvers/, scanParams/, and
tests/ found no implementation of VLQ \(T\)-pair collider limits,
ATLAS/CMS direct-search likelihoods, HEPData exclusion contours, or a
top-partner mass filter. Adjacent evidence is limited to KK-scale and
flavor-filter plumbing: quarkConstraints/modern/scan.py:1230
constructs M\_KK for scan points, quarkConstraints/modern/scan.py:1492
builds failing-system lists from flavor ratios, quarkConstraints/modern/scan.py:1503
restricts those systems to \(\epsilon_K,K,B_d,B_s,D^0\), and
quarkConstraints/modern/evaluation.py:643 starts the \(M_{KK}\)
resolution used for KK-gluon matching. The current quark scope is summarized
as MFV fitting at quarkConstraints/README.md:34, KK-scale conventions
at quarkConstraints/README.md:36, and a \(\Delta F=2\) exclusion
slice at quarkConstraints/README.md:38; none of those lines is a
collider top-partner filter.Implementation difficulty
HIGH. A faithful live constraint needs either a simplified
acceptance map over \({\cal B}(Wb),{\cal B}(Zt),{\cal B}(Ht)\) or an external
reinterpretation workflow such as CheckMATE, MadAnalysis5, SModelS, or a
collaboration likelihood/HEPData grid. It also needs an RS spectrum model
that predicts the lightest custodial \(T\) mass, width, and branching
fractions. The current code has neither collider-event machinery nor a
top-partner spectrum/decay module.
Reason: A faithful CR003 implementation needs collider reinterpretation data or an external tool chain plus an RS top-partner spectrum, width, and branching-ratio calculation. The repo currently has low-energy flavor filters and KK-gluon matching, not event-level acceptance or VLQ exclusion contours.
Key references
PDGLive2026\_Q009TPP\_TprimePair;
ATLAS2024\_VLQPairWb\_Run2;
ATLAS2023\_VLQPairZt\_Run2;
CMS2023\_VLQPairLeptonic\_Run2;
ATLAS2017\_VLQPairWb\_13TeV;
ATLAS2018\_VLQPairMultiB;
ATLAS2018\_VLQPairHadronic;
ContinoServant2008\_TopPartners;
QuarkScanMethodology2026\_MKKEnvelope.