Strong QCD corrections to p-wave quarkonium decays

We have calculated one-loop QCD corrections to the annihilation widths of P-wave quarkonium states into hadrons and into two photons. Comparison with accurate experimental data may lead to a clear test of perturbative QCD if α_S turns out to be small enough for reasonable convergence.     

On the corrections of the wave function in weakly bound quarkonium

A non-relativistic quark-antiquark system with perturbative gluonic interactions (quarkonium) is considered, which allows a systematic expansion in the strong coupling constant α_s. In a non-abelian gauge theory, non-trivial corrections of the wave function already occur to O(α_s). We emphasize the existence of a renormalization, which is “natural” for such a system leaving only little freedom in the choice of the renormalization point Λ. The general corrections to O(α_s) including coulombic binding are presented. An explicit application to the lowest-order gluonic corrections of the leptonic decay of quarkonium is made. In this process the new term is sometimes much larger than the gluonic correction at the photon vertex and it varies greatly between different coulombic (S-wave) bound states.     

QCD corrections to electroweak annihilation decays of superheavy quarkonia

QCD corrections to all the allowed decays of superheavy groundstate quarkonia into electroweak gauge and Higgs bosons are presented. For quick estimates, approximations that reproduce the exact results within less than at worst one percent are also given.     

Strong radiative corrections to annihilations of quarkonia in QCD

The significance of the lowest-order QCD prediction for the annihilations of heavy quark-antiquark bound states is analyzed. The calculation of the leading strong radiative corrections to the hadronic versus electromagnetic annihilation rate ratio R of pseudoscalar quarkonium is presented. In terms of the coupling constant α_s, as defined in the minimal subtraction scheme, we find R = R⁽⁰⁾(1 + 22.14α_s/π). The physical significance of this result is discussed by comparing it with the calculation of the non-leading effects in α_s on the scaling violations in deep inelastic scattering. A bad convergence of the relative perturbative expansion is found, demanding for its safe application a value of the relevant momentum definitely higher than that of charmonium physics.     

Order alphas4 QCD corrections to Z and tau decays

Using recently developed methods for the evaluation of five-loop amplitudes in perturbative QCD, corrections of order alphas4 for the nonsinglet part of the cross section for electron-positron annihilation into hadrons and for the decay rates of the Z boson and the tau lepton into hadrons are evaluated. The new terms lead to a significant stabilization of the perturbative series, to a reduction of the theory uncertainly in the strong coupling constant alphas, as extracted from these measurements, and to a small shift of the central value, moving the two central values closer together. The agreement between two values of alphas measured at vastly different energies constitutes a striking test of asymptotic freedom. Combining the results from Z and tau decays we find alphas(MZ)=0.1198+/-0.0015 as one of the most precise and presently only result for the strong coupling constant in order alphas4.     

Thep - \bar p decays ofP-wave quarkonium and the helicity characteristics of massless QCD

We consider the exclusive \(p - \bar p\) decays of the quarkoniumP-states. Due to the helicity conservation of massless QCD the \(p - \bar p\) mode is forbidden in this limit for the¹ P ₁ and the³ P ₀ states. The angular distributions for the decays of the remaining states in the cascade \(^3 S\prime _1 \to \gamma ^3 P_J \to \gamma p\bar p\) are specific to QCD and can serve as a test of the theory. The same is true of the formation process \(p\bar p \to ^3 P_J \to ^3 S_1 \gamma \) . In lowest order QCD we obtain overall branching ratios for charmonium of the order of 10^?4.     

Supersymmetric signature in quarkonium decays

We calculate the heavy quarkonium decay widths for decays to scalar fermion-scalar antifermion pairs. In the light of the supersymmetric interpretation of the recently observed monojets, these decays could be observable in the forthcoming e⁺−e⁻ colliding beam machines. The scalar lepton-scalar antilepton pairs produced by toponium decays is comparable to those produced by direct photon exchanges. The decays of the scalar pair into an electron-positron (or muon-antimuon) pair (carrying about one-half of the total beam energy) together with the missing photinos will be a clean signature of supersymmetry.     

Light pseudoscalar and scalar particles in quarkonium radiative decays: Estimates from QCD sum rules

From QCD sum rules the model-independent estimates of widths of radiative decaysJ/ψ→Pγ,Sγ and ?→Pγ,Sγ are obtained with 0(α_S) accuracy, whereP (S) is a light pseudoscalar (scalar) particle of the axion (Higgs boson) type. Deviation of QCD predictions from the Wilczek nonrelativistic formula for these widths turned out to be inessential.     

Two-loop QCD corrections to the longitudinal structure function

We calculate the fourth-order corrections to the longitudinal Wilson coefficient in deep inelastic scattering (for the non-singlet case). We use off-mass-shell states to control collinear singularities. A table of numerical results is presented for different numbers of quark flavours, and from these results we obtain the total next-to-leading order contributions to the moments of the longitudinal structure function.     

A note on the QCD corrections to forward-backward asymmetries of heavy-quark jets inZ decays

The measurement of the forward-backward asymmetries of heavy quarks provides one of the most precise determinations of sin² _W inZ decays. We discuss in detail the one-loop QCD radiative corrections to these asymmetries. Results are given for single heavy-quark jet asymmetries and asymmetries of the thrust axis, as well as for heavy-quark two-jet final states.     

Higher order QCD corrections to the energy-energy correlation function

We calculate theO(α _s ² correction to the energy-energy correlation cross section using a Sterman-Weinberg type resolution criterion to account for higher-order/nonperturbative effects. We find that the energy-energy correlation function as well as the asymmetry is sensitive to the choice of resolution parameters.     

Small QCD corrections in inclusive 0−+ quarkonium decay for the bound-state renormalization scheme

A consistent field theoretic computation of the first-order correction to the total decay of a non-relativistic heavy quarkonium state must consider contributions from the annihilation amplitude, with a typical scale of the order of the quark mass m, and from the bound-state wave function, where the typical scale is of the order of the Bohr momentum α_sm. Therefore, not only the latter smaller scale is the one to be taken for the total decay rate, but also a quite specific renormalization, the “bound-state renormalization scheme”, must be used for a computation of the total inclusive decay rate of 0^?+→hadrons. Due to important cancellations between large individual contributions, the net result turns out to be small, encouraging the use of pure perturbative QCD in such systems.