Top Quark Physics

TL;DR

This work surveys top quark physics at future $e^+e^-$ colliders, focusing on decay properties and pair production near threshold. It derives precise predictions for the total width and energy/angular distributions of decay products, highlighting how leptons and neutrinos serve as probes of the $tbW$ vertex and top polarization. It then treats $t\bar t$ production near threshold with a Green-function approach to extract the top mass and strong coupling, while examining the influence of QCD potentials and possible Higgs effects. Overall, the study emphasizes polarization observables, lepton-energy spectra, and threshold scans as powerful tools for testing the Standard Model and constraining fundamental parameters.

Abstract

Top quark studies at future $e^+e^-$ colliders are considered. Two issues are discussed: {a --}Some results are presented on the decays of top quarks. Energy distributions of charged leptons and neutrinos in $t\to bW\to be^+ν$ and jets in $t\to bW\to b\bar du$ decays are sensitive to the structure of $tbW$ vertex. Distributions of charged leptons from top decays are particularly useful in polarization studies whereas neutrinos are sensitive to deviations from the Standard Model. {b --}Recent calculations are reviewed on the top quark pair production in $e^+e^-$ annihilation. The differential cross sections in the threshold region can lead to an accurate determination of the top quark mass and the interquark potential. The effects of the top-Higgs Yukawa coupling and some higher order QCD corrections are also under control.

Figures (10)

• Figure 1: Total cross sections for the reaction $e^+e^-\to e^-\bar{\nu} t\bar{b}(e^+\nu \bar{t} b)$ as the function of the top quark mass Boos.
• Figure 2: Distribution of $W$ energy for $m_t=$174 GeV without (dashed line) and with (solid line) QCD corrections
• Figure 3: Energy distributions a) ${\rm A_l}(x_\ell)$ of the charged lepton and b) ${\rm A}_\nu(x_\nu)$ of the neutrino for the standard model V-A coupling ($\kappa^2=0$) and an admixture of V+A current ($\kappa^2=$0.1) for $y=$0.25 and $\alpha_s=$0.11.
• Figure 4: Angular-energy distribution functions in the Standard Model ($\kappa^2=0$) and for the admixture of V+A current ($\kappa^2=$0.1): a) ${\rm B_l}(x_\ell)$ for the charged lepton and b) ${\rm B}_\nu(x_\nu)$ for the neutrino, $y$=0.25 and $\alpha_s$=0.11.
• Figure 5: Cross section for $t\bar{t}$ production in units of $\sigma_{point}$ including resonance and QCD enhancement and initial state radiation.