Top Quark Width Research Articles

Erratum: Top quark width: Theoretical update

A critical assessment of the available calculations of the top quark width is presented. QCD corrections, the finite mass of the $b$ quark and the effect of the $W$ width are included as well as the electroweak corrections. The relative importance of these corrections is demonstrated for the realistic range of top masses. For the QCD corrected decay rate we use the formulae from \cite{JK1} and include the electroweak correction taken from \cite{DS}. Our results differ from those available in the literature because all the later calculations ignored the effect of W width discussed earlier in \cite{JK1}~. This leads to an effect comparable in size to the electroweak correction.

Supersymmetric QCD contributions to the top quark width.

Virtual contributions of squark-gluino coupling to the top quark decay width $\ensuremath{\Gamma}(t\ensuremath{\rightarrow}{W}^{+}b)$ and $\ensuremath{\Gamma}(t\ensuremath{\rightarrow}{H}^{+}b)$ are calculated to one-loop order in the minimal supersymmetric standard model. The corrections are found to reduce the top quark width. If the squarks and gluinos take their lowest allowed masses, the correction to $\ensuremath{\Gamma}(t\ensuremath{\rightarrow}{W}^{+}b)$ can reach the level of 1% and the correction to $\ensuremath{\Gamma}(t\ensuremath{\rightarrow}{H}^{+}b)$ is typically a few percent.

Single top quark production at LEP200

The single top quark production rate and its dependence on the mass of the top at the energies achievable at LEP200 are will be 190 (210) GeV, the discovery limit reaches m t ≈ 165 (180) GeV. Enough data for the top quark mass and width measurements will be collected if m t ⩽ 145 (165) GeV, and the measurement precision can be higher than at LHC.

Top quark width: Theoretical update.

A critical assessment of the available calculations of the top quark width is presented. QCD corrections, the finite mass of the $b$ quark, and the effect of the $W$ width are included as well as the electroweak corrections. The relative importance of these corrections is demonstrated for a realistic range of top quark masses. For the QCD corrected decay rate we use the formulas from Eilam et al. and include the electroweak correction taken from Fujii. Our results differ from those available in the literature because all the later calculations ignored the effect of the $W$ width discussed earlier by Eilam et al. This leads to an effect comparable in size to the electroweak correction.

Axial-vector-coupling contribution to toponium resonances.

We study the effect of [ital t] [bar t] Z axial-vector coupling to the [ital t[bar t]] pair production process near threshold at [ital e][sup +][ital e[minus]] colliders. [ital P]-wave resonance states produced via axial-vector coupling interfere with [ital S]-wave resonance states due to the large top-quark width. This interference gives rise to the forward-backward asymmetry below threshold which grows from 0 to [similar to]7% as [ital m][sub [ital t]] is increased from 100 to 200 GeV. Its [alpha][sub [ital s]] dependence is magnified simultaneously. The measurement of the forward-backward asymmetry may allow an efficient determination of [alpha][sub [ital s]] for a relatively heavy top quark.

Radiative corrections to the top quark width within two-Higgs-doublet models

The electroweak one-loop contributions to the top decay width Γ(t → W + b) are discussed in the extension of the standard model with two Higgs doublets. In the general two-Higgs-doublet model, the non-standard corrections due to the extra Higgs bosons can be significantly larger (10% and more) than in the minimal model, depending strongly on m t and on the mass of the neutral scalar boson with non-standard couplings. The Higgs sector of the minimal supersymmetric standard model, on the other hand, does not give rise to large extra corrections: only for large tan β and M H + ⋍ 100 GeV they reach the level of 1%, otherwise they are negligibly small.

Soft gluon radiation in [formula omitted

We present a detailed analysis of soft gluon radiation in e + e − → t t → bW + bW − . Regions of validity for the perturbative formulation are carefully defined and the “antenna pattern” decomposition of the radiation is used as a tool for finding the kinematical configurations of the final-state particles which are most sensitive to the top-quark width.

QCD corrections to t-->W++b.

The {ital O}({alpha}{sub {ital s}}) QCD corrections to the process {ital t}{r arrow}{ital W}{sup +}{ital b} are calculated in the standard model for a heavy top quark. For {ital m}{sub {ital W}}/{ital M}{sub {ital t}}{lt}0.8, the corrections reduce the partial width by 10% relative to the tree-level result. This reduction of the top-quark width enhances the signal for {ital t{bar t}} bound-state resonances near threshold in {ital e}{sup +}{ital e{minus}} collisions, studied recently by Strassler and Peskin.

Measuring the heavy top quark width in by soft gluon radiation

Abstract The deviation of the top quark width from the value predicted by the standard model might provide the first clue to the mechanism of electroweak symmetry breaking. In QCD perturbation theory the radiation pattern in e + e − →t t has been calculated. It is shown that by measuring the angular distribution of soft gluon bremsstrahlung one can probe the top quark width.