Abstract (data abstract)

A search for flavor-changing neutral-current couplings between a top quark, an up or charm quark and a $Z$ boson is presented, using proton-proton collision data at $\sqrt{s} = 13$ TeV collected by the ATLAS detector at the Large Hadron Collider. The analyzed dataset corresponds to an integrated luminosity of 139 fb$^{-1}$. The search targets both single-top-quark events produced as $gq\rightarrow tZ$ (with $q = u, c$) and top-quark-pair events, with one top quark decaying through the $t \rightarrow Zq$ channel. The analysis considers events with three leptons (electrons or muons), a $b$-tagged jet, possible additional jets, and missing transverse momentum. The data are found to be consistent with the background-only hypothesis and 95% confidence-level limits on the $t \rightarrow Zq$ branching ratios are set, assuming only tensor operators of the Standard Model effective field theory framework contribute to the $tZq$ vertices. These are $6.2 \times 10^{-5}$ ($13\times 10^{-5}$) for $t\rightarrow Zu$ ($t\rightarrow Zc$) for a left-handed $tZq$ coupling, and $6.6 \times 10^{-5}$ ($12\times 10^{-5}$) in the case of a right-handed coupling. These results are interpreted as 95% CL upper limits on the strength of corresponding couplings, yielding limits for $|C_{uW}^{(13)*}|$ and $|C_{uB}^{(13)*}|$ ($|C_{uW}^{(31)}|$ and $|C_{uB}^{(31)}|$) of 0.15 (0.16), and limits for $|C_{uW}^{(23)*}|$ and $|C_{uB}^{(23)*}|$ ($|C_{uW}^{(32)}|$ and $|C_{uB}^{(32)}|$) of 0.22 (0.21), assuming a new-physics energy scale $\Lambda_\text{NP}$ of 1 TeV.

Table 7

Data from Table 7 of paper

10.17182/hepdata.145074.v1/t1

Summary of the signal strength $\mu$ parameters obtained from the fits to extract LH and RH results for the FCNC...
Table 8

Data from Table 8 of paper

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Observed and expected 95% CL limits on the FCNC $t\rightarrow Zq$ branching ratios and the effective coupling strengths for different...
Figure 02a

Data from Figure 2a of paper

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Comparison between data and background prediction before the fit (Pre-Fit) for the mass of the SM top-quark candidate in SR1....
Figure 02b

Data from Figure 2b of paper

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Comparison between data and background prediction before the fit (Pre-Fit) for the mass of the FCNC top-quark candidate in SR1....
Figure 02c

Data from Figure 2c of paper

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Comparison between data and background prediction before the fit (Pre-Fit) for the mass of the SM top-quark candidate in SR2....
Figure 02d

Data from Figure 2d of paper

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Comparison between data and background prediction before the fit (Pre-Fit) for the transverse momentum of the Z boson candidate in...
Figure 03a

Data from Figure 3a of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...
Figure 03b

Data from Figure 3b of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...
Figure 03c

Data from Figure 3c of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...
Figure 03d

Data from Figure 3d of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...
Figure 04a

Data from Figure 4a of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZc LH coupling extraction. The...
Figure 04b

Data from Figure 4b of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZc LH coupling extraction. The...
Figure 04c

Data from Figure 4c of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZc LH coupling extraction. The...
Figure 04d

Data from Figure 4d of paper

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZc LH coupling extraction. The...
Auxiliary Figure 01a

Data from Auxiliary Figure 1a

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...
Auxiliary Figure 01b

Data from Auxiliary Figure 1b

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...
Auxiliary Figure 01c

Data from Auxiliary Figure 1c

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Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...
Auxiliary Figure 01d

Data from Auxiliary Figure 1d

10.17182/hepdata.145074.v1/t18

Comparison between data and background prediction after the fit to data (Post-Fit) for the FCNC tZu LH coupling extraction. The...

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Table 8

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Auxiliary Figure 01a

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