Johann H. Kuhn

Production and decay properties of ultra-heavy quarks☆

Abstract The widths of ultra-heavy quarks that can be decay into W, Z or Higgs bosons are discussed. If the lifetimes become much shorter than the typical strong interaction time scale Λ −1 QCD ∼ 10 −23 s, then open-flavor hadrons and quarkonium bound states cannot be formed any more. Consequences for the jet evolution are investigated. On the other hand, if such quarks can decay only through tiny mixing angles - as it could happen for sequential down-type quarks and for SU(2) singlet quarks in E 6 models - then these bound states do form. Production rates for quarkonia in e + e - annihilation and in hadronic collisions are estimated and their decay signatures are discussed.

QCD corrections to semileptonic decays of heavy quarks

Abstract A formula for the semileptonic decay rate of heavy quarks is derived which includes the first-order gluon corrections, the W-boson propagator effects and the non-zero mass of the quark produced in the decay process.

Lepton Spectra from Heavy Quark Decay

Abstract Analytic formulas are derived for the QCD corrections to the electron and neutrino spectra from the weak decay of a heavy up or down type quark. The effect of the W-propagator and of the mass of the quark in the final state are incorporated. As special case the limit of local four fermion interaction, relevant for charm and bottom decays, is considered and contrasted with earlier results in the literature.

Rare decays of the Z0

We study radiative and Higgs decay modes of the Z0 into hypothetical heavy quark bound states (onia). In general, we find that the rates for these decays are extremely small. However, in some cases, there is some enhancement if the onia are rather near in mass to the Z0. We examine the experimental prospects for detecting, by these means, spin-parity onium states which are otherwise difficult to reach or discovering Higgs mesons. We conclude, unfortunately, that these prospects are not very bright.

τ Decays to pions

Semileptonic τ decays to two and three pions are considered. Based on recent data for the pion form factor a new prediction for Γ(τ→vπ-0)/Γ(τ→veve) of 1.32±0.05 is derived. The chiral model-supplemented by vector dominance-is used to predict rate and differential distributions for the three pion mode in good agreement with present data. The parity violating asymmetry which has been predicted theoretically and observed experimentally is studied and found to be fairly insensitive towards the details of the model for the hadronic decays.

Electromagnetic annihilation of e+e− into quarkonium states with even charge conjugation

Abstract We calculate the production of narrow resonances with even charge conjugation 3 P J =1,2 in e + e − annihilation in the quarkonium and vectordominance models. We give unitarity bounds for Γ( 3 P J → e + e − ) in terms of Γ( 3 P J → γγ) and Γ( 3 P J → e + e − ) . The electromagnetic production dominates through the neutral current at low energies independent of details of the model. For masses above 10 GeV the situation is reversed.

Mass corrections to the Z decay rate

In this note radiative corrections to the total hadronic decay rate of the τ-lepton are studied employing perturbative QCD and the operator product expansion. We calculate quadratic quark mass corrections to the decay rate rationRτ to the order0(αs2m2) and find that they contribute appreciably to the Cabbibo supressed decay modes of the τ-lepton. We also discuss corrections of mass dimensionD=4, where we emphasize the need of a suitable choice of the renormalization scale of the quark and gluon condensates.

QCD corrections to the Z decay rate

Abstract Corrections to the Z decay rate are calculated in perturbative QCD. The axial vector current induced rate differs in order α s 2 from the rates induced by the vector current and the electromagnetic current respectively. The additional term is calculated analytically. It is shown that the dominant O( α s 3 ) correction is odentical with the correction for R = σ had / σ point at low energies and the (small) differences are estimated.

Lepton Spectra From Decays of Polarized Top Quarks

Abstract QCD corrections to the double differential lepton spectrum from the decay of a polarized top quark are calculated. It is shown that the factorization into energy-dependent and angular-dependent parts holds true also for the QCD corrected spectrum to a high degree of accuracy. A compact formula is given for the remaining small corrections.

QCD corrections to the axial part of the decay Z rate

Abstract As a consequence of the large splitting between top and bottom quark masses QCD corrections to the axial part of the Z decay rate into b quarks differ from those to the vector part in order α s 2 . Analytic results for these two-loop corrections are presented.