Searches for anomalous $tqZ$ couplings from the trilepton signal of $tZ$ associated production at the 14 TeV LHC

TL;DR

This paper explores the potential to detect anomalous top quark couplings to the Z boson at the 14 TeV LHC through specific trilepton signals, setting bounds on rare decay branching ratios.

Contribution

It provides new sensitivity estimates for FCNC top decays to uZ and cZ at the LHC, improving constraints with higher luminosity data.

Findings

Probes top FCNC decay branching ratios down to 1.3×10⁻⁴ for t→uZ at 100 fb⁻¹.

Achieves sensitivity to t→cZ branching ratios of 4.2×10⁻⁴ at 100 fb⁻¹.

Improves bounds to 2.2×10⁻⁵ for t→uZ at 3000 fb⁻¹.

Abstract

We investigate the observability of the top anomalous $tqZ$ couplings via the trilepton signatures at the Large Hadron Collider~(LHC) with the center-of-mass energy of 14 TeV. We focus on signals of the $tZ$ associated production with the decay mode $t\to W^{+}b\to b\ell^{+}\nu_{\ell}$, $Z\to \ell^{+}\ell^{-}$, and $t\bar{t}$ production with the decay mode $\bar{t}\to Z(\to \ell^{+}\ell^{-})\bar{q}$ and $t\to b\ell^{+}\nu_{\ell}$, where $\ell=e, \mu$ and $q$ reflects up and charm quarks. It is shown that at $3\sigma$ level, the FCNC top quark decay branching ratios can be probed at, respectively, about $Br(t\to uZ) \leq 1.3\times 10^{-4}$ and $Br(t\to cZ) \leq 4.2\times 10^{-4}$ with the integrated luminosity of 100 fb$^{-1}$, and probed down to $Br(t\to uZ) \leq 2.2\times 10^{-5}$ and $Br(t\to cZ) \leq 8\times 10^{-5}$ for the high-luminosity LHC with 3000 fb$^{-1}$.