Search for pair-production of vector-like quarks in $pp$ collision events at $\sqrt{s}=13$ TeV with at least one leptonically decaying $Z$ boson and a third-generation quark with the ATLAS detector

ATLAS Collaboration

Preprint

PUBDB-2022-06839

Search for pair-production of vector-like quarks in $pp$ collision events at $\sqrt{s}=13$ TeV with at least one leptonically decaying $Z$ boson and a third-generation quark with the ATLAS detector

ATLAS Collaboration (Collaboration author)DESY*

2022

[10.3204/PUBDB-2022-06839]

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Please use a persistent id in citations: doi:10.3204/PUBDB-2022-06839

Report No.: CERN-EP-2021-207; arXiv:2210.15413

Abstract: A search for the pair-production of vector-like quarks optimized for decays into a $Z$ boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to 139 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV, collected in 2015-2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a $Z$ boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of $b$-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted $W$, $Z$, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners $T$ and $B$ of the top and bottom quarks, respectively. In the singlet model, the limits allow $m_T > 1.27$ TeV and $m_B > 1.20$ TeV. In the doublet model, allowed masses are $m_T > 1.46$ TeV and $m_B >1.32$ TeV. In the case of 100% branching ratio for $T\rightarrow Zt$ and 100% branching ratio for $B\rightarrow Zb$, the limits allow $m_T > 1.60$ TeV and $m_B > 1.42$ TeV, respectively.

Keyword(s): p p: scattering ; p p: colliding beams ; family: 3 ; Z0: transverse momentum ; transverse momentum: high ; quark: postulated particle ; quark: vector particle ; quark: pair production ; quark: decay modes ; Z0: leptonic decay ; jet: bottom ; bottom: particle identification ; top: particle identification ; jet: transverse momentum: high ; branching ratio ; final state: ((n)jet dilepton) ; final state: ((n)jet 3lepton) ; background ; ATLAS ; calibration ; sensitivity ; CERN LHC Coll ; Higgs particle ; singlet ; doublet ; quark: mass: lower limit ; neural network ; data analysis method ; experimental results ; quark --> Z0 top ; quark --> Z0 bottom ; 13000 GeV-cms

Note: 26 pages in total, 8 figures, 4 tables, submitted to PLB. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2018-58

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