Probing tqZ anomalous couplings in the trilepton signal at the HL-LHC, HE-LHC and FCC-hh

Abstract

We investigate the prospects for discovering the Flavour Changing Neutral Current (FCNC) $tqZ$ couplings via two production processes yielding trilepton signals: top quark pair production $pp\to t\bar{t}$ with one top decaying to the $Z$ boson and one light jet and the anomalous single top plus $Z$ boson production process $pp\to tZ$. We study these channels at various successors of the Large Hadron Collider~(LHC), i.e., the approved High-Luminosity LHC (HL-LHC) as well as the proposed High-Energy LHC~(HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh). We perform a full simulation for the signals and the relevant Standard Model (SM) backgrounds and obtain limits on the Branching Ratios (BRs) of $t\to qZ(q=u,c)$, eventually yielding a trilepton final state through the decay modes $t\to b{W}^{+}\to b{\ell }^{+}{\nu }_{\ell }$ and $Z\to {\ell }^{+}{\ell }^{-}$. The upper limits on these FCNC BRs at 95\% Confidence Level (CL) are obtained at the HL-LHC with $\sqrt{s}=14$ TeV and 3 ab${}^{-1}$, at the HE-LHC with $\sqrt{s}=27$ TeV and 15 ab${}^{-1}$ as well as at the FCC-hh with $\sqrt{s}=100$ TeV and 30 ab${}^{-1}$.

21 pages, 6 figures, 8 tables, to appear in Chinese Physics C

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• Top-philic heavy resonances in four-top final states and their EFT interpretation
• Rare and exclusive few-body decays of the Higgs, Z, W bosons, and the top quark
• New flavor physics in di- and tri-lepton events from single-top at the LHC and beyond
• Two-proton emission systematics
• Soft-gluon corrections for $tqZ$ production
• NLO QCD and EW corrections to off-shell $\mathrm{tZj}$ production at the LHC
• $CP$ violation in the $HZZ$ vertex and left-right asymmetries
• Explaining the $b\to s{\ell }^{+}{\ell }^{-}$ anomalies in $Z^{\prime }$ scenarios with top-FCNC couplings
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• Semi-microscopic theory of two proton emission
• Searching for top-philic heavy resonances in boosted four-top final states