Search for pair-produced vector-like top and bottom partners in events with large missing transverse momentum in pp collisions with the ATLAS detector

The ATLAS collaboration
Eur.Phys.J.C 83 (2023) 719, 2023.

Abstract
A search for pair-produced vector-like quarks using events with exactly one lepton ($e$ or $\mu$), at least four jets including at least one $b$-tagged jet, and large missing transverse momentum is presented. Data from proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb$^{-1}$, are analysed. Vector-like partners $T$ and $B$ of the top and bottom quarks are considered, as is a vector-like $X$ with charge +5/3, assuming their decay into a $W$, $Z$, or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section of $T$ and $B$ quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 TeV assuming mass-degenerate VLQs and branching ratios corresponding to the weak-isospin doublet model, and 1.47 TeV (1.46 TeV) for exclusive $T \rightarrow Zt$ ($B/X \rightarrow Wt$) decays. In addition, lower limits on the $T$ and $B$ quark masses are derived for all possible branching ratios.

  • $TT \rightarrow ZtZt$ cross-section limits

    Figure 7a

    10.17182/hepdata.137656.v1/t1

    Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $T\bar{T}$ and...

  • $BB \rightarrow WtWt$ cross-section limits

    Figure 7b

    10.17182/hepdata.137656.v1/t2

    Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $B\bar{B}$ and...

  • $TT$ cross-section limits for the singlet model

    Figure 7c

    10.17182/hepdata.137656.v1/t3

    Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $T\bar{T}$ in...

  • $BB$ cross-section limits for the singlet model

    Figure 7d

    10.17182/hepdata.137656.v1/t4

    Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $B\bar{B}$ in...

  • $TT$ cross-section limits for the doublet model

    Figure 7e

    10.17182/hepdata.137656.v1/t5

    Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production for $T\bar{T}$ in...

  • $QQ$ cross-section limits for the doublet model

    Figure 7f

    10.17182/hepdata.137656.v1/t6

    Expected and observed upper limits at 95% CL on the cross section of vector-like quark pair production, considereing both $T\bar{T}$...

  • Expected lower limits on the VLT mass

    Figure 8a

    10.17182/hepdata.137656.v1/t7

    Expected 95% CL lower limits on the vector-like top quark mass as a function of the branching ratios into $Wb$...

  • Observed lower limits on the VLT mass

    Figure 8b

    10.17182/hepdata.137656.v1/t8

    Observed 95% CL lower limits on the vector-like top quark mass as a function of the branching ratios into $Wb$...

  • Expected lower limits on the VLB mass

    Figure 8c

    10.17182/hepdata.137656.v1/t9

    Expected 95% CL lower limits on the vector-like bottom quark mass as a function of the branching ratios into $Hb$...

  • Observed lower limits on the VLB mass

    Figure 8d

    10.17182/hepdata.137656.v1/t10

    Observed 95% CL lower limits on the vector-like top quark mass as a function of the branching ratios into $Hb$...

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