T. Teubner

Angular distributions of massive quarks and leptons close to threshold

Abstract Predictions for the angular distribution of massive quarks and leptons are presented, including QCD and QED corrections. Recent results for the fermionic part of the two-loop corrections to the electromagnetic form factors are combined with the BLM scale fixing prescription. Two distinctly different scales arise as arguments of αs(μ2) near threshold: the relative momentum of the quarks governing the soft gluon exchange responsible for the Coulomb potential, and a large momentum scale approximately equal to twice the quark mass for the corrections induced by transverse gluons. Numerical predictions for charmed, bottom, and top quarks are given. One obtains a direct determination of αV(Q2), the coupling in the heavy quark potential, which can be compared with lattice gauge theory predictions. The corresponding QED results for τ pair production allow for a measurement of the magnetic moment of the τ and could be tested at a future τ-charm factory.

Polarization in top quark pair production near threshold

Abstract The polarization dependent momentum distributions of top quarks and their decay products are calculated for t t production at future e + e − colliders with polarized beams. The Green function formalism is applied to this reaction near energy threshold. The Lippmann-Schwinger equations for the S -wave and P -wave Green functions are solved numerically for the QCD chromostatic potential given by the two-loop formula at large momentum transfers and Richardson ansatz at intermediate and small ones. It is demonstrated that for the longitudinally polarized electron beam an optimally polarized sample of top quarks can be produced.

Massive quark production in electron positron annihilation to order \(\alpha_s^2\)

Abstract. Recent analytical and numerical results for the three-loop polarization function allow to present a phenomenological analysis of the cross section for massive quark production in electron positron annihilation to order

Radiation of heavy quarks

\alpha_s^2

Momentum distributions int\(\bar t\) production and decay near threshold

. Numerical predictions based on fixed order perturbation theory are presented for charm and bottom production above 5 and 11.5 GeV, respectively. The contribution from these energy regions to

Hadron radiation in leptonic Z decays

\alpha(M_Z^2)

Polarization in top pair production and decay near threshold

, the running QED coupling constant at scale

QCD Potential and ttbar Threshold Cross Section --- Status Report ---

M_Z

Comment on the Average Momentum of Top Quarks in the Threshold Region

, are given. The dominant terms close to threshold, i.e. in an expansion for small quark velocity

Momentum distributions in production and decay near threshold

\beta