# ${{\boldsymbol t}^{\,'}}$(2/3)-quark/hadron mass limits in ${{\boldsymbol p}}{{\overline{\boldsymbol p}}}$ and ${{\boldsymbol p}}{{\boldsymbol p}}$ collisions INSPIRE search

VALUE (GeV) CL% DOCUMENT ID TECN  COMMENT
$\bf{> 1280}$ 95 1
 2019 AQ
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit t}}$ ) = 1
$>1370$ 95 2
 2019 BW
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit h}}{{\mathit t}}$ ) = 1
$>980$ 95 3
 2018 CE
ATLS ${}\geq{}2{{\mathit \ell}}$ + $\not E_T$ + ${}\geq{}1{{\mathit b}}$j
$> 1010$ 95 4
 2018 CL
ATLS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit h}}{{\mathit t}}$ ) = 1
$> 1030$ 95 5, 6
 2018 CP
ATLS 2,3${{\mathit \ell}}$, singlet model
$> 1210$ 95 5, 7
 2018 CP
ATLS 2,3${{\mathit \ell}}$, doublet model
$\bf{> 1310}$ 95 8, 9
 2018 CR
ATLS singlet ${{\mathit t}^{\,'}}$. ATLAS combination
$\bf{> 1370}$ 95 8, 10
 2018 CR
ATLS ${{\mathit t}^{\,'}}$ in a weak isospin doublet (${{\mathit t}^{\,'}},{{\mathit b}^{\,'}}$). ATLAS combination.
$> 1140$ 95 11
 2018 BM
CMS ${{\mathit W}}{{\mathit b}}$ , ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit h}}{{\mathit t}}$ modes
$> 845$ 95 12
 2018 Q
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit q}}$ ) = 1 (${{\mathit q}}={{\mathit d}},{{\mathit s}}$)
$\bf{> 1295}$ 95 13
 2018 W
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) = 1
$>1160$ 95 14
 2017 L
ATLS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit t}}$ ) = 1
$>860$ 95 15
 2017 AU
CMS
$> 770$ 95 16
 2015 AR
ATLS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) = 1
$> 590$ 95 17
 2015 BY
ATLS ${{\mathit W}}{{\mathit b}}$ , ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit h}}{{\mathit t}}$ modes
$> 745$ 95 18
 2015 AI
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit h}}{{\mathit t}}$ ) = 1
$> 735$ 95 19
 2014 AZ
ATLS B( ${{\mathit b}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit t}}$ ) = 1
$> 700$ 95 20
 2014 A
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) = 1
$> 706$ 95 20
 2014 A
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit t}}$ ) = 1
$> 782$ 95 20
 2014 A
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit h}}{{\mathit t}}$ ) = 1
$> 350$ 95 21
 2012 BC
ATLS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit q}}$ )=1 (${{\mathit q}}={{\mathit d}},{{\mathit s}},{{\mathit b}}$)
$> 420$ 95 22
 2012 C
ATLS ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit X}}{{\mathit t}}$ (${\mathit m}_{{{\mathit X}}}<$ 140 GeV)
$> 685$ 95 23
 2012 BH
CMS ${\mathit m}_{{{\mathit b}^{\,'}}}$ = ${\mathit m}_{{{\mathit t}^{\,'}}}$
$> 557$ 95 24
 2012 P
CMS ${{\mathit t}^{\,'}}$ ${{\overline{\mathit t}}^{\,'}}$ $\rightarrow$ ${{\mathit W}^{+}}{{\mathit b}}{{\mathit W}^{-}}{{\overline{\mathit b}}}$ $\rightarrow$ ${{\mathit b}}{{\mathit \ell}^{+}}{{\mathit \nu}}{{\overline{\mathit b}}}{{\mathit \ell}^{-}}{{\overline{\mathit \nu}}}$
• • • We do not use the following data for averages, fits, limits, etc. • • •
$> 656$ 95 25
 2013 F
ATLS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) = 1
$> 625$ 95 26
 2013 I
CMS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit t}}$ ) = 1
$> 404$ 95 27
 2012 AR
ATLS B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) = 1
$> 570$ 95 28
 2012 BC
CMS ${{\mathit t}^{\,'}}$ ${{\overline{\mathit t}}^{\,'}}$ $\rightarrow$ ${{\mathit W}^{+}}{{\mathit b}}{{\mathit W}^{-}}{{\overline{\mathit b}}}$
$> 400$ 95 29
 2011 AH
CDF ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit X}}{{\mathit t}}$ (${\mathit m}_{{{\mathit X}}}<$ 70 GeV)
$> 358$ 95 30
 2011 AL
CDF ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$
$> 340$ 95 30
 2011 AL
CDF ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit q}}$ (${{\mathit q}}={{\mathit d}},{{\mathit s}},{{\mathit b}}$)
$> 360$ 95 31
 2011 O
CDF ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit X}}{{\mathit t}}$ (${\mathit m}_{{{\mathit X}}}<$ 100 GeV)
$> 285$ 95 32
 2011 Q
D0 ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit q}}$ (${{\mathit q}}={{\mathit d}},{{\mathit s}},{{\mathit b}}$)
$> 256$ 95 33, 34
 2008 H
CDF ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit q}}$
1  SIRUNYAN 2019AQ based on 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. Pair production of vector-like ${{\mathit t}^{\,'}}$ is seached for with one ${{\mathit t}^{\,'}}$ decaying into ${{\mathit Z}}{{\mathit t}}$ and the other ${{\mathit t}^{\,'}}$ decaying into ${{\mathit W}}{{\mathit b}}$ , ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit h}}{{\mathit t}}$ . Events with an opposite-sign lepton pair consistent with coming from ${{\mathit Z}}$ and jets are used. Mass limits are obtained for a variety of branching ratios of ${{\mathit t}^{\,'}}$.
2  SIRUNYAN 2019BW based on 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. The limit is for the pair-produced vector-like ${{\mathit t}^{\,'}}$ using all-hadronic final state. The analysis is made for the ${{\mathit W}}{{\mathit b}}$ , ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit h}}{{\mathit t}}$ modes and mass limits are obtained for a variety of branching ratios.
3  AABOUD 2018CE based on 36.1 fb${}^{-1}$ of proton-proton data taken at $\sqrt {s }$ = 13 TeV. Events including a same-sign lepton pair are used. The limit is for a singlet model, assuming the branching ratios of ${{\mathit t}^{\,'}}$ into ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit W}}{{\mathit b}}$ and ${{\mathit H}}{{\mathit t}}$ as predicted by the model.
4  AABOUD 2018CL based on 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. The limit is for the pair-produced vector-like ${{\mathit t}^{\,'}}$ using all-hadronic final state. The analysis is also made for the ${{\mathit W}}{{\mathit b}}$ , ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit h}}{{\mathit t}}$ modes and mass limits are obtained for a variety of branching ratios.
5  AABOUD 2018CP based on 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. Pair and single production of vector-like ${{\mathit t}^{\,'}}$ are seached for with at least one ${{\mathit t}^{\,'}}$ decaying into ${{\mathit Z}}{{\mathit t}}$ . In the case of B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit Z}}{{\mathit t}}$ ) = 1, the limit is ${\mathit m}_{{{\mathit t}^{\,'}}}$ $>$ 1340 GeV.
6  The limit is for the singlet model, assuming that the branching ratios into ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit W}}{{\mathit b}}$ , and ${{\mathit H}}{{\mathit t}}$ add up to one.
7  The limit is for the doublet model, assuming that the branching ratios into ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit W}}{{\mathit b}}$ , and ${{\mathit H}}{{\mathit t}}$ add up to one.
8  AABOUD 2018CR based on 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. A combination of searches for the pair-produced vector-like ${{\mathit t}^{\,'}}$ in various decay channels ( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ , ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit h}}{{\mathit t}}$ ). Also a model-independent limit is obtained as ${\mathit m}_{{{\mathit t}^{\,'}}}$ $>$ 1.31 TeV, assuming that the branching ratios into ${{\mathit Z}}{{\mathit t}}$ , ${{\mathit W}}{{\mathit b}}$ and ${{\mathit h}}{{\mathit t}}$ add up to one.
9  The limit is for the singlet ${{\mathit t}^{\,'}}$.
10  The limit is for ${{\mathit t}^{\,'}}$ in a weak isospin doublet (${{\mathit t}^{\,'}},{{\mathit b}^{\,'}}$) and $\vert {{\mathit V}}_{{{\mathit t}^{\,'}}{{\mathit b}}}\vert$ ${}\ll$ $\vert {{\mathit V}}_{{{\mathit t}}{{\mathit b}^{\,'}}}\vert$.
11  SIRUNYAN 2018BM based on 35.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. The limit is for the pair-produced vector-like ${{\mathit t}^{\,'}}$. Three channels (single lepton, same-charge 2 leptons, or at least 3 leptons) are considered for various branching fraction combinations. Assuming B( ${{\mathit t}}{{\mathit H}}$ ) = 1, the limit is 1270 GeV and for B( ${{\mathit t}}{{\mathit Z}}$ ) = 1 it is 1300 GeV.
12  SIRUNYAN 2018Q based on 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 8 TeV. The limit is for the pair-produced vector-like ${{\mathit t}^{\,'}}$ that couple only to light quarks. Constraints for other decay channels ( ${{\mathit Z}}{{\mathit q}}$ and ${{\mathit H}}{{\mathit q}}$ ) are also given in the paper.
13  SIRUNYAN 2018W based on 35.8 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. The limit is for the vector-like ${{\mathit t}^{\,'}}$ pair-produced by strong interaction using lepton-plus-jets mode and assuming that B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) is 100%. Generally the measurement sets upper limits on the product of the production cross section and branching faction to ${{\mathit W}}{{\mathit b}}$ for any new pair-produced heavy quark decaying to this channel as a narrow resonance.
14  AABOUD 2017L based on 36.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. No signal is found in the search for heavy quark pair production that decay into ${{\mathit Z}}{{\mathit t}}$ followed by ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit \nu}}$ in the events with one lepton, large $\not E_T$, and ${}\geq{}$4 jets. The lower mass limit 0.87 (1.05) TeV is obtained for the singlet (doublet) model with other possible decay modes.
15  SIRUNYAN 2017AU based on 2.3-2.6 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 13 TeV. Limit on pair-produced singlet vector-like ${{\mathit t}^{\,'}}$ using one lepton and several jets. The mass bound is given for a ${{\mathit t}^{\,'}}$ transforming as a singlet under the electroweak symmetry group, assumed to decay through ${{\mathit W}}$, ${{\mathit Z}}$ or Higgs boson (which decays to jets) and to a third generation quark. For a doublet, the limit is $>$830 GeV. Other limits are also given in the paper.
16  AAD 2015AR based on 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 8 TeV. Used lepton-plus-jets final state. See Fig. 20 for mass limits in the plane of B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit H}}{{\mathit t}}$ ) vs. B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) from a combination of ${{\mathit t}^{\,'}}$ ${{\overline{\mathit t}}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}{+}$ ${{\mathit X}}$ and ${{\mathit t}^{\,'}}$ ${{\overline{\mathit t}}^{\,'}}$ $\rightarrow$ ${{\mathit H}}{{\mathit t}}{+}$ ${{\mathit X}}$ searches. Any branching ratio scenario is excluded for mass below 715 GeV.
17  AAD 2015BY based on 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 8 TeV. Limit on pair-produced vector-like ${{\mathit t}^{\,'}}$ assuming the branching fractions to ${{\mathit W}}$, ${{\mathit Z}}$, and ${{\mathit h}}$ modes of the singlet model. Used events containing ${}\geq{}2{{\mathit \ell}}$ + $\not E_T$ + ${}\geq{}$2j (${}\geq{}$1 ${{\mathit b}}$) and including a same-sign lepton pair.
18  KHACHATRYAN 2015AI based on 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 8 TeV. The search exploits all-hadronic final states by tagging boosted Higgs boson using jet substructure and ${{\mathit b}}$-tagging.
19  Based on 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 8 TeV. No significant excess over SM expectation is found in the search for pair production or single production of ${{\mathit t}^{\,'}}$ in the events with dilepton from a high $p_T$ ${{\mathit Z}}$ and additional jets (${}\geq{}$ 1 ${{\mathit b}}$-tag). If instead of B( ${{\mathit b}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit t}}$ ) = 1 an electroweak singlet with B( ${{\mathit b}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit t}}$ ) $\sim{}$ 0.45 is assumed, the limit reduces to 685 GeV.
20  Based on 19.5 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 8TeV. The ${{\mathit t}^{\,'}}$ quark is pair produced and is assumed to decay into three different final states of , , and . The search is carried out using events with at least one isolated lepton.
21  Based on 1.04 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. No signal is found for the search of heavy quark pair production that decay into ${{\mathit W}}$ and a quark in the events with dileptons, large $\not E_T$, and ${}\geq{}$2 jets.
22  Based on 1.04 fb${}^{-1}$ of data in ${{\mathit p}}{{\mathit p}}$ collisions at 7 TeV. AAD 2012C looked for ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production followed by ${{\mathit t}^{\,'}}$ decaying into a top quark and ${{\mathit X}}$, an invisible particle, in a final state with an isolated high-P$_{T}$ lepton, four or more jets, and a large missing transverse energy. No excess over the SM ${{\mathit t}}{{\overline{\mathit t}}}$ production gives the upper limit on ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production cross section as a function of ${\mathit m}_{{{\mathit t}^{\,'}}}$ and ${\mathit m}_{{{\mathit X}}}$. The result is obtained for B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit t}}$ ) = 1.
23  Based on 5 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. CHATRCHYAN 2012BH searched for QCD and EW production of single and pair of degenerate 4'th generation quarks that decay to ${{\mathit W}}{{\mathit b}}$ or ${{\mathit W}}{{\mathit t}}$ . Absence of signal in events with one lepton, same-sign dileptons or tri-leptons gives the bound. With a mass difference of 25 GeV/c${}^{2}$ between ${\mathit m}_{{{\mathit t}^{\,'}}}$ and ${\mathit m}_{{{\mathit b}^{\,'}}}$, the corresponding limit shifts by about $\pm20$ GeV/c${}^{2}$.
24  Based on 5.0 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. CHATRCHYAN 2012P looked for ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production events with two isolated high $p_T$ leptons, large $\not E_T$, and 2 high $p_T$ jets with ${{\mathit b}}$-tag. The absence of signal above the SM background gives the limit for B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) = 1.
25  Based on 4.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. No signal is found for the search of heavy quark pair production that decay into ${{\mathit W}}$ and a ${{\mathit b}}$ quark in the events with a high $p_T$ isolated lepton, large $\not E_T$ and at least 3 jets (${}\geq{}$ 1 ${{\mathit b}}$-tag). Vector-like quark of charge 2/3 with 400 $<$ ${\mathit m}_{{{\mathit t}^{\,'}}}$ $<$ 550 GeV and B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) $>$ 0.63 is excluded at 95$\%$ CL.
26  Based on 5.0 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. CHATRCHYAN 2013I looked for events with one isolated electron or muon, large $\not E_T$, and at least four jets with large transverse momenta, where one jet is likely to originate from the decay of a bottom quark.
27  Based on 1.04 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. No signal is found in the search for pair produced heavy quarks that decay into ${{\mathit W}}$ boson and a ${{\mathit b}}$ quark in the events with a high $p_T$ isolated lepton, large $\not E_T$ and at least 3 jets (${}\geq{}$1 ${{\mathit b}}$-tag).
28  Based on 5.0 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. CHATRCHYAN 2012BC looked for ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production events with a single isolated high $p_T$ lepton, large $\not E_T$ and at least 4 high $p_T$ jets with a ${{\mathit b}}$-tag. The absence of signal above the SM background gives the limit for B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit W}}{{\mathit b}}$ ) = 1.
29  Based on 5.7 fb${}^{-1}$ of data in ${{\mathit p}}{{\overline{\mathit p}}}$ collisions at 1.96 TeV. AALTONEN 2011AH looked for ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production followed by ${{\mathit t}^{\,'}}$ decaying into a top quark and ${{\mathit X}}$, an invisible particle, in the all hadronic decay mode of ${{\mathit t}}{{\overline{\mathit t}}}$ . No excess over the SM ${{\mathit t}}{{\overline{\mathit t}}}$ production gives the upper limit on ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production cross section as a function of ${\mathit m}_{{{\mathit t}^{\,'}}}$ and ${\mathit m}_{{{\mathit X}}}$. The result is obtained for B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit X}}{{\mathit t}}$ ) = 1.
30  Based on 5.6 fb${}^{-1}$ of data in ppbar collisions at 1.96 TeV. AALTONEN 2011AL looked for ${{\mathit \ell}}$ + ${}\geq{}$4j events and set upper limits on ${\mathit \sigma (}$ ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}{)}$ as functions of ${\mathit m}_{{{\mathit t}^{\,'}}}$.
31  Based on 4.8 fb${}^{-1}$ of data in ${{\mathit p}}{{\overline{\mathit p}}}$ collisions at 1.96 TeV. AALTONEN 2011O looked for ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production signal when ${{\mathit t}^{\,'}}$ decays into a top quark and ${{\mathit X}}$, an invisible particle, in ${{\mathit \ell}}$ + $\not E_T$ + jets channel. No excess over the SM ${{\mathit t}}{{\overline{\mathit t}}}$ production gives the upper limit on ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}$ production cross section as a function of ${\mathit m}_{{{\mathit t}^{\,'}}}$ and ${\mathit m}_{{{\mathit X}}}$. The result is obtained for B( ${{\mathit t}^{\,'}}$ $\rightarrow$ ${{\mathit X}}{{\mathit t}}$ ) = 1.
32  Based on 5.3 fb${}^{-1}$ of data in ${{\mathit p}}{{\overline{\mathit p}}}$ collisions at 1.96 TeV. ABAZOV 2011Q looked for ${{\mathit \ell}}$ + $\not E_T$ + ${}\geq{}$4j events and set upper limits on ${\mathit \sigma (}$ ${{\mathit t}^{\,'}}{{\overline{\mathit t}}^{\,'}}{)}$ as functions of ${\mathit m}_{{{\mathit t}^{\,'}}}$.
33  Searches for pair production of a new heavy top-like quark ${{\mathit t}^{\,'}}$ decaying to a ${{\mathit W}}$ boson and another quark by fitting the observed spectrum of total transverse energy and reconstructed ${{\mathit t}^{\,'}}$ mass in the lepton + jets events.
34  HUANG 2008 reexamined the ${{\mathit t}^{\,'}}$ mass lower bound of 256 GeV obtained in AALTONEN 2008H that assumes B( ${{\mathit b}^{\,'}}$ $\rightarrow$ ${{\mathit q}}{{\mathit Z}}$ ) = 1 for ${{\mathit q}}$ = ${{\mathit u}}$, ${{\mathit c}}$ which does not hold when ${\mathit m}_{{{\mathit b}^{\,'}}}<{\mathit m}_{{{\mathit t}^{\,'}}}−{\mathit m}_{{{\mathit W}}}$ or the mixing sin$^2(\theta _{ {{\mathit b}} {{\mathit t}^{\,'}} })$ is so tiny that the decay occurs outside of the vertex detector. Fig. 1 gives that lower bound on ${\mathit m}_{{{\mathit t}^{\,'}}}$ in the plane of sin$^2(\theta _{ {{\mathit b}} {{\mathit t}^{\,'}} })$ and ${\mathit m}_{{{\mathit b}^{\,'}}}$.
References:
 SIRUNYAN 2019AQ
EPJ C79 364 Search for vector-like quarks in events with two oppositely charged leptons and jets in proton-proton collisions at $\sqrt{s} =$ 13 TeV
 SIRUNYAN 2019BW
PR D100 072001 Search for pair production of vectorlike quarks in the fully hadronic final state
 AABOUD 2018CR
PRL 121 211801 Combination of the searches for pair-produced vector-like partners of the third-generation quarks at $\sqrt{s} =$ 13 TeV with the ATLAS detector
 AABOUD 2018CL
PR D98 092005 Search for pair production of heavy vector-like quarks decaying into hadronic final states in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector
 AABOUD 2018CE
JHEP 1812 039 Search for new phenomena in events with same-charge leptons and $b$-jets in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector
 AABOUD 2018CP
PR D98 112010 Search for pair- and single-production of vector-like quarks in final states with at least one $Z$ boson decaying into a pair of electrons or muons in $pp$ collision data collected with the ATLAS detector at $\sqrt{s} = 13$ TeV
 SIRUNYAN 2018W
PL B779 82 Search for pair production of vector-like quarks in the bW$\overline{\mathrm{b}}$W channel from proton-proton collisions at $\sqrt{s} =$ 13 TeV
 SIRUNYAN 2018BM
JHEP 1808 177 Search for vector-like T and B quark pairs in final states with leptons at $\sqrt{s} =$ 13 TeV
 SIRUNYAN 2018Q
PR D97 072008 Search for vectorlike light-flavor quark partners in proton-proton collisions at $\sqrt s$ =8??TeV
 AABOUD 2017L
JHEP 1708 052 Search for Pair Production of Vector-Like Top Quarks in Events with One Lepton, Jets, and Missing Transverse Momentum in $\sqrt {s }$ = 13 TeV ${{\mathit p}}{{\mathit p}}$ Collisions with the ATLAS Detector
 SIRUNYAN 2017AU
JHEP 1711 085 Search for Pair Production of Vector-Like and Quarks in Single-Lepton Final States using Boosted Jet Substructure in Proton-Proton Collisions at $\sqrt {s }$ = 13 TeV
JHEP 1510 150 Analysis of Events with ${\mathit {\mathit b}}$-Jets and a Pair of Leptons of the Same Charge in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV with the ATLAS Detector
JHEP 1508 105 Search for Production of Vector-Like Quark Pairs and of Four Top Quarks in the Lepton-plus-Jets Final State in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV with the ATLAS Detector
 KHACHATRYAN 2015AI
JHEP 1506 080 Search for Vector-Like Quarks Decaying to Top Quarks and Higgs Bosons in the All-Hadronic Channel using Jet Substructure
JHEP 1411 104 Search for Pair and Single Production of New Heavy Quarks that Decay to a ${{\mathit Z}}$ Boson and a Third-Generation Quark in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV with the ATLAS Detector
 CHATRCHYAN 2014A
PL B729 149 Inclusive Search for a Vector-Like t Quark with Charge ${2\over 3}$ in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV
PL B718 1284 Search for Pair Production of Heavy Top-Like Quarks Decaying to a High-$p_T$ ${{\mathit W}}$ Boson and a ${\mathit {\mathit b}}$ Quark in the Lepton Plus Jets Final State at $\sqrt {s }$ = 7 TeV with the ATLAS Detector
 CHATRCHYAN 2013I
JHEP 1301 154 Search for Heavy Quarks Decaying into a Top Quark and a ${{\mathit W}}$ or ${{\mathit Z}}$ Boson using Lepton + Jets Events in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 7 TeV
PRL 108 261802 Search for Pair Production of a Heavy Up-Type Quark Decaying to a ${{\mathit W}}$ Boson and a ${\mathit {\mathit b}}$ Quark in the lepton+jets Channel with the ATLAS Detector
PRL 108 041805 Search for New Phenomena in ${\mathit {\mathit t}}{\mathit {\overline{\mathit t}}}$ Events with Large Missing Transverse Momentum in Proton$−$Proton Collisions at $\sqrt {s }$ = 7$~$TeV with the ATLAS Detector
PR D86 012007 Search for Pair-Produced Heavy Quarks Decaying to ${{\mathit W}}{\mathit {\mathit q}}$ in the Two-Lepton Channel at $\sqrt {s }$ = 7 TeV with the ATLAS Detector
 CHATRCHYAN 2012P
PL B716 103 Search for Heavy, Top-Like Quark Pair Production in the Dilepton Final State in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 7 TeV
 CHATRCHYAN 2012BH
PR D86 112003 Combined Search for the Quarks of a Sequential Fourth Generation
 CHATRCHYAN 2012BC
PL B718 307 Search for Pair Produced Fourth-Generation Up-Type Quarks in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 7 TeV with a Lepton in the Final State
 AALTONEN 2011AH
PRL 107 191803 Search for New ${{\mathit T}^{\,'}}$ Particles in Final States with Large Jet Multiplicities and Missing Transverse Energy in ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions at $\sqrt {s }$ = 1.96 TeV
 AALTONEN 2011AL
PRL 107 261801 Search for a Heavy Toplike Quark in ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions at $\sqrt {s }$ = 1.96 TeV
 AALTONEN 2011O
PRL 106 191801 Search for Production of Heavy Particles Decaying to Top Quarks and Invisible Particles in ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions at $\sqrt {s }$ = 1.96 TeV
 ABAZOV 2011Q
PRL 107 082001 Search for a Fourth Generation Quark in ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions at = 1.96 TeV
 AALTONEN 2008H
PRL 100 161803 Search for Heavy Toplike Quarks using Lepton Plus Jets Events in 1.96 TeV ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions