R. Rückl

1/n Expansion for Exclusive and Inclusive Charm Decays

We systematically apply the 1/N expansion (N being the number of colours) to exclusive and inclusive charm decays and develop a diagrammatic language in which the leading contributions can be clearly identified and calculated. Keeping only the leading terms in 1/N makes the usual approach compatible with the data on exclusive decays and gives τ(D+)/τ(D0) ≈ 02 and BSL(D0) ≈ 10%. 0382 1537 V 3 We also show that the recent analysis of exclusive charm decays of Bauer and Stech can be justified to a certain extent in this approach. The possible non-leading effects are briefly discussed.

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.

D-meson lifetimes and decays

Abstract We discuss the theoretical implications of having the D + lifetime be much greater than that of the D 0 . A consistent phenomenology of D-decay obtains if one assumes sextet dominance and strong color clustering.

Perturbative QCD correction to the B → π transition form factor

Abstract We report on the perturbative O ( α s ) correction to the light-cone QCD sum rule for the B → π transition form factor f + . The correction to the product f B f + in leading twist approximation is found to be about 30%, that is similar in magnitude to the corresponding O ( α s ) correction in the two-point sum rule for f B . The resulting cancellation of large QCD corrections in f + eliminates one important uncertainty in the sum-rule prediction for this form factor.

Quarkonium sum rules: A critical reappraisal

Abstract We reanalyze the ITEP charmonium sum rules incorporating experimental errors and allowing for variations in input parameters. The necessity of a gluon condensate term is apparent for the ratio sum rules, but the presence or absence of this term cannot be established using the moment sum rules. Plausibility arguments are given for trusting the results of the ratio sum rules and the advantages of mass-independent double ratio sum rules are stressed. Sum rules for the bottomonium system are also analyzed and the results are shown to be consistent with what is obtained in the charmonium sector.

Energy flow and energy correlations in deep inelastic scattering

Abstract We study two examples of infrared-safe quantities in deep inelastic scattering: the flow of energy in a given angular range and the energy-energy angular pattern. We derive expressions for these quantities in perturbative QCD, to order αs, and show explicitly their infrared safety. Our formulas for the angular energy flow and the energy-energy angular pattern depend only on well-defined QCD factors and on the deep inelastic structure functions. To gauge whether or not these perturbative QCD results are applicable to present day data, we estimate in a simple model the effects of hadronization and primordial parton transverse momentum. In general these non-perturbative effects mask the resulting QCD pattern at present energies, but vanish more rapidly at higher energies than the QCD effects. However, we point out two examples where it may be possible to test the perturbative QCD predictions with available data. One of them involves studying the x-dependence of the azimuthal asymmetry of the energy flow. The other involves studying the angular width of the energy-energy correlation function.

Muoproduction of J/ψ and the photon-gluon scattering process: γvg→J/ψg

Abstract Recent data on muoproduction of J/ψ reported by the European Muon Collaboration are used to examine the perturbative QCD subprocess γ v g→J/ ψ g as a possible production mechanism. We find that for sufficiently inelastic J/ψs this process can account for the observed rates and distributions. We argue, however, that in total only about 10 to 20% of the observed J/ψ yield is due to this source.

Effects of QCD on the Cabibbo patterns in B-meson decays

Abstract The Cabibbo patterns for B-meson decays in the Kobayashi-Maskawa model are altered once QCD corrections are included. We estimate these QCD effects and discuss possible experimental signatures.

Direct lepton production by soft virtual bremsstrahlung

Abstract Internal conversion of soft virtual bremsstrahlung, calculated in an essentially model independent infrared limit, yields numerous low mass-low energy lepton pairs. The resulting single lepton spectra rise sharply towards p T = 0 for large angles θ cm and towards x = 0 for θ cm = 0°. The ratio e π for p T ⩽ 400 MeV/ c exhibits roughly the experimentally observed properties.

Dimensional regularization techniques and their uses in calculating infrared safe weak decay processes

Abstract The calculation of corrections to total weak decay rates, although expected to be free of infrared and mass singularities, is rendered difficult by the appearance of precisely these singularities at intermediate stages in the calculation. We demonstrate the effectiveness of using dimensional regularization techniques for handling these problems. As a specific non-trivial example, we study gluonic corrections to the decay of a heavy quark, of mass M, into light quarks of masses mi. Neglecting terms of order (mi/M)2, we find, to first order in αs, for the total decay rate Γ = G 2 M 5 64π 3 {1− 2α s 3π (π 2 − 31 4 )} .