Radiative corrections in heavy quarkonia

We investigate radiative corrections in heavy quarkonia and calculate relativistic corrections which are not taken into account in earlier papers. It appears that these terms cannot be neglected as compared to the usually calculated radiative corrections and lead to a considerable contribution to the level splittings.     

On the Lorentz nature of confinement in heavy—light quarkonia

The Lorentz nature of the effective interquark interaction in a heavy—light quarkonium is studied using the vacuum correlators method and the generalized Nambu—Jona-Lasinio potential quark model. An effective scalar interaction is demonstrated to appear self-consistently owing to chiral-symmetry breaking and to dominate for low-lying states in the bound-state spectrum. The relation between such an effective interquark interaction and the QCD string approach is discussed. On the contrary, the upper part of this spectrum is found to be governed by the spatial Lorentz vector interaction which leads to a degeneracy for the states with opposite parity—the so-called restoration of chiral symmetry for excited hadrons. The text was submitted by the author in English.     

Direct decays of heavy quarkonia

The branching ratios are evaluated of the ψ (3770) and (4S) decays into ππ, , ωπ⁰, ωη, ωη ′, π, η, η′, , . They arise due to the transition through the real intermediate states and , respectively. It is shown that some branching ratios exceed the three-gluon one by an order of magnitude. The rates of the decays ,

Full-size image

and are evaluated also. τ-C and B factories coul be good tools for studying all decays mentioned.     

Di-pion emission in heavy quarkonia decays

The dipion spectrum for the ϒ(nS) → ϒ(n′S) transition with n < 4 has the form dw/dq ∼ (phase space) |η − x|², with x = q ² − 4m _π² / (ΔM)² − 4m _π² < q ² ≡ M _ππ², and ΔM = M(nS) − M(n′S). The parameter η is calculated and the spectrum is shown to reproduce the experimental data for all three types of decays: 3 → 1, 2 → 1, and 3 → 2 with η ≈ 0.5, 0, and −3, respectively. The text was submitted by the author in English.     

On equal constituent quark masses in different heavy quarkonia potential models

An Azcarraga-Lukierski supersymmetric particle model, which is invariant with respect to theN=2 extended SuperPoincare group, is quantised by the method of Dirac brackets. The central charges, which satisfy the spin reducing conditions, are conjugate to additional bosonic coordinates in the superspace. The resulting superwavefunction doublet is in one-to-one correspondence with the superfield expansion of Sohnius describing the Fayet hypermultiplet.     

Hadronic decays of excited heavy quarkonia

We construct an effective Lagrangian for the hadronic decays of a heavy excited s-wave-spin-one quarkonium Ψ′ into a lower s-wave-spin-one state Ψ. We show that reasonable fits to the measured invariant mass spectra in the charmonium and bottomonium systems can be obtained within this framework. The mass dependence of the various terms in the Lagrangian is discussed on the basis of a quark model.     

On the possibility of detecting gluon condensation from the spectra of heavy quarkonia

We compute the effect of the gluon condensate on the spectra of heavy quarkonia, taking into account the condensate correlation length. We compare the results obtained for the hydrogen-like model with a more realistic model. The effects are shown to be very small both in bottomonium and toponium.     

Radiative decays and the nature of heavy quarkonia

We argue that the photon spectra in radiative decays of various heavy quarkonium states provide important information on their nature. If two of these states are in the strong coupling regime, we are able to produce a parameter-free model-independent formula, which holds at next-to-leading order and includes both direct and fragmentation contributions. When the formula is checked against recent CLEO data it favors Y(2S) and Y(3S) in the strong coupling regime and disfavors Y(1S) in it.     

Generating heavy quarkonia in a perturbative QCD cascade

We present an implementation of heavy quarkonium production within a perturbative QCD cascade based on the Color Dipole Cascade model. We consider the processes most relevant in the context of the ψ′ surplus at the Tevatron; g → ψ′ and c → ψ′ in the color-singlet model and g → ψ′ through the color-octet mechanism. Our implementation is, however, easily extendible to other quarkonia and other production mechanisms. Where comparison is possible we find good agreement with analytical calculations. We present some suggestions for measurements at the Tevatron that would be sensitive to the shape of the fragmentation functions. Our calculations indicate that such measurements could be used to test the color-octet mechanism solution to the ψ′ surplus at the Tevatron.     

Spectrum of heavy quarkonia in an instanton medium

The energy-level shift in heavy-quarkonium systems that is caused by fluctuations of vacuum gluon fields is estimated by simulating these fields by an instanton liquid. The use of the corresponding vacuum correlation function makes it possible to go beyond the dipole approximation. The width of energy levels with respect to decay to e ⁺ e ^? pairs is also given. It is shown that, both for bottomonium and for charmonium systems, an instanton medium can ensure a scale of shifts and widths of levels that is compatible with experimental data. In particular, it is indicated that a sizable logarithmic contribution at short distances is peculiar to the instanton vacuum.     

Comment on the hadronic decay of excited heavy quarkonia

We make comments on [1], and provide partial wave analysis to the decays of excited heavy S-wave quarkonia into the basic quarkonia state plus . It is revealed that there exist contributions of D-wave transition in , and by using the data-fitting results in [1]. A possible experimental method to measure the D-wave directly is discussed. Received: 14 May 1998 / Published online: 21 September 1998