CR002 $pp \to T_{5/3} \bar{T}_{5/3} \to W^+ t W^- \bar{t}$
Pair production of exotic-charge $T_{5/3}$ custodial top partner Status REVIEWED VERIFIED High Code: NO Priority Medium
PDG / equivalent values
| Observable | Value | Year | Experiment / source | Provenance |
|---|---|---|---|---|
| m(t'(5/3)) lower limit for pair-produced vector-like X/B $ \to $ Wt | > 1460 95% CL (lower_limit) | 2023 | ATLAS | source ↑ |
| strongest mass lower limit for mass-degenerate vector-like doublet benchmark | > 1590 95% CL (lower_limit) | 2023 | ATLAS | source ↑ |
| $m(X_5/3$) lower limit, right-handed coupling | > 1330 95% CL (lower_limit) | 2019 | CMS | source ↑ |
| $m(X_5/3$) lower limit, left-handed coupling | > 1300 95% CL (lower_limit) | 2019 | CMS | source ↑ |
| $m(T_5/3$) lower limit from pair production | > 1190 95% CL (lower_limit) | 2018 | ATLAS | source ↑ |
| $m(T_5/3$) lower limit when single production is included | > 1600 95% CL (lower_limit) | 2018 | ATLAS | source ↑ |
| $m(X_5/3$) lower limit, right-handed coupling | > 1020 95% CL (lower_limit) | 2017 | CMS | source ↑ |
| $m(X_5/3$) lower limit, left-handed coupling | > 990 95% CL (lower_limit) | 2017 | CMS | source ↑ |
| $m(X_5/3$) lower limit from same-sign dilepton search | > 800 95% CL (lower_limit) | 2014 | CMS | source ↑ |
Why this constrains the RS scan
CR002 is a direct LHC constraint on the custodial top-partner spectrum, not a
low-energy \(\Delta F=1\) or \(\Delta F=2\) observable. It is therefore most
useful as a cross-check on non-anarchic or compressed custodial-RS spectra in
which the lightest fermion partners can be much lighter than the KK gauge
scale. In an anarchic-flavor RS scan, the repo-local this repository quark methodology
already reports
\[
M_{KK}^{\min,p50}(\,g_\ast=3\,)=47.26~\mathrm{TeV},
\]
so a \(T_{5/3}\) direct-search reach near the \(1.5~\mathrm{TeV}\) scale is
not the leading constraint on the default anarchic-flavor ensemble.
The collider number constrains a physical custodial-partner mass under
specific LHC simplified-model assumptions. Mapping it onto \(M_{KK}\) needs a
model-dependent relation between the fermion-partner spectrum, top
compositeness, and the gauge KK scale; it should not be treated as a direct
cut on the same \(M_{KK}\) variable used by the quark-flavor scan.
What's changed since the original paper
The LHC program closely follows the Contino--Servant and Mrazek--Wulzer
same-sign-dilepton motivation:
- CMS arXiv:1312.2391 established the first LHC same-sign-dilepton charge-\(5/3\) limit, excluding masses below \(800~\mathrm{GeV}\) at \(\sqrt{s}=8~\mathrm{TeV}\) for exclusive \(tW\) decay.
- CMS arXiv:1705.10967 moved the search to \(\sqrt{s}=13~\mathrm{TeV}\) and combined same-sign dilepton with single-lepton final states, reaching \(1.02~\mathrm{TeV}\) and \(0.99~\mathrm{TeV}\) for the right- and left-handed coupling benchmarks.
- ATLAS arXiv:1807.11883 used same-charge leptons and \(b\)-jets to set the \(1.19~\mathrm{TeV}\) pair-production limit and to demonstrate the stronger but coupling-dependent single-production interpretation.
- CMS arXiv:1810.03188 increased the dataset to \(35.9~\mathrm{fb}^{-1}\) and produced the \(1.33~\mathrm{TeV}\) / \(1.30~\mathrm{TeV}\) CMS Run-2 limits.
- ATLAS arXiv:2212.05263 used the full Run-2 one-lepton plus missing-transverse-momentum search to provide the current PDG-leading \(1.46~\mathrm{TeV}\) exclusive \(B/X\to Wt\) limit.
Validity and model dependence
The pair-production cross section is QCD dominated, so the production rate is
less sensitive to the \(T_{5/3}Wt\) electroweak coupling than single
production. The acceptance and the quoted mass limit are nevertheless tied to
the assumed prompt decay pattern, top-partner width, branching fractions, and
event topology. If the \(T_{5/3}\) has sizable non-\(tW\) decays, cascade
decays into other custodial states, a broad width, or a compressed spectrum,
the simple PDG mass bound is not automatically applicable. The stronger
single-production reinterpretation is explicitly coupling dependent and should
be catalogued separately from the pair-production CR002 entry if it is ever
implemented.
Code coverage in this repo
NO. A collider-specific grep over
quarkConstraints/,
qcd/, flavorConstraints/, neutrinos/,
yukawa/, warpConfig/, solvers/,
scanParams/, and tests/ found no \(T_{5/3}\),
\(X_{5/3}\), VLQ, top-partner, collider, or LHC direct-search implementation.
The adjacent code is low-energy RS machinery: quarkConstraints/modern/scan.py:1230
maps \(\Lambda_{\mathrm{IR}}\) to \(M_{KK}\), quarkConstraints/modern/scan.py:1254
stores that scan-point \(M_{KK}\), quarkConstraints/couplings.py:103
defines mass-basis KK-gluon couplings, quarkConstraints/couplings.py:116
describes the enhanced 5D KK-gluon coupling, and
quarkConstraints/deltaf2.py:1 identifies the implemented exclusion
slice as a tree-level KK-gluon-inspired \(\Delta F=2\) benchmark. The
matching layer itself notes at quarkConstraints/modern/matching.py:240
that it is not a full operator-complete EFT/RG package.
Linked evidence (opens GitHub blob at flavor-catalog-website/2026q2):
Implementation difficulty
HIGH. A faithful implementation would need at least a recast pipeline:
event generation for \(T_{5/3}\bar T_{5/3}\), decay and branching-ratio
control, detector-level efficiencies or public likelihoods, and validation
against ATLAS/CMS exclusion tables. External reinterpretation tools such as
CheckMATE, MadAnalysis5, or SModelS would be more realistic than a
hand-written scan cut.
Reason: A faithful LHC direct-search constraint needs event generation, detector-level efficiencies or recast likelihoods, branching-ratio scans, and/or external reinterpretation tools such as CheckMATE, MadAnalysis5, SModelS, or collaboration likelihood material.
Key references
PDGEncoderQ009\_TPrime5Over3;
ATLAS2023\_VLQ\_MET;
CMS2019\_X53\_Run2;
ATLAS2018\_SameCharge\_BJets;
CMS2017\_X53\_13TeV;
CMS2014\_X53\_8TeV;
ContinoServant2008\_TopPartners;
MrazekWulzer2009\_TopPartners.