Radiative transitions and the P wave levels in charmonium

A value of $\text{1}\text{2}$ or less for the ratio $\text{[E(2}{}^{\mathrm{++}}\text{) ? E(1}{}^{\mathrm{++}}\text{)]}\text{[E(1}{}^{\mathrm{++}}\text{) ? E(0}{}^{\mathrm{++}}\text{)]}$ of the P level splittings in approximate agreement with the assignment of the states at 3.41, 3.50 and 3.55 to the 0⁺⁺,and 2⁺⁺ P-wave levels, is obtained with a short-range Coulomb (Lorentz vector) potential together with a long-range linear (Lorentz scalar) confining potential. The radiative transition widths Γ(ψ′ → 3.41 + γ), Γ(ψ′ → 3.50 + γ), Γ(χ′ → 3.55 + γ) are significantly smaller than those obtained in previous (one-channel) charmonium calculations. The best results were obtained by allowing the Coulomb coupling constant α_s to have a momentum dependence suggested by asymptotic freedom formulae.     

On the decay of θ mesons in charmonium models

We derive a new formula for the decay rate of the ψ mesons by properly treating the dependence of lowest order electromagnetic annihilation on the quark-antiquark bound state wave function. Results are presented for currently used non-relativistic potentials models for charmonium. In all cases substantial corrections to previous estimates from commonly used formulas occur. Our results are of relevance also for hadronic decay via gluons in QCD and weak decay of pseudoscalar mesons.     

On ηc line shape in charmonium transitions

The line shapes to observe ηc in charmonium transitions, I.e.,ψ(2S), J/ψ→γηc, are investigated. The ηc line shapes in exclusive decays or by observing the inclusive photon spectrum are given. The sensitivities to measure the ηc resonance parameters are also evaluated. With more than two thousand ηc events observed, the precision of the ηc decay width measurement will be improved by better than 3%. However, the uncertainties associated with the ηc modified line shapes will dominate the systematic errors and this will prohibit precision mass and width measurements.     

Pseudoscalars in the charmonium model

We take the recently found charmonium state at 2.976 GeV to be the η _c and show that it can be included in a charmonium model with relativistic corrections which reproduces the s-wave spectrum, the leptonic widths Γ(V→e ⁺ e^?) and the p-wave splittings. The upsilon spectrum is discussed as are the effects of radial and pseudoscalar mixing.     

Exclusive processes of charmonium production and charmonium wave functions

Results obtained by studying the properties of the leading-twist wave functions for the S- and P-wave states of charmonia are presented. Wave-function models that can be used to calculate various processes involving the production of these mesons were constructed on the basis of these investigations. Calculations for some exclusive processes of charmonium production were performed within the models in question.     

Photoproduction of charmonium

Photoproduction of ortho and para charm-anticharm bound states is considered in the framework of the Cheng-Wu picture. Non-Abelian gauge gluons mediate the interaction between the c$\text{c}$-pair and the nucleon. The angular distributions of ψ_c and η_c are determined. The influence of multigluon exchanges and quark mass variation is studied.     

Scanning the quark-gluon plasma with charmonium

We suggest the variation of charmonium production rate with Feynman x(F) in heavy ion collisions as a novel and sensitive probe for the properties of the created matter. Final state interactions with the comoving matter create a minimum at x(F) = 0, which is especially deep and narrow if a quark-gluon plasma is formed. While a strong effect is predicted at SPS, at the RHIC energy it overlaps with the expected peak formed by shadowing effects and needs comparison with pA data. We predict a steep dependence on centrality and suggest that this new probe is complementary to the dependence on transverse energy, and is more sensitive to a scenario of final state interactions.     

Possible open channel effects in the charmonium spectrum

QCD sum rules are used to give absolute bounds for the semi leptonic decay widths of the heavy mesonsD ⁺ andF ⁺ into η and η′. This method, very stable and reliable in those cases where a heavy mass scale is involved, does not rely on any quark gluon picture of the above decays. While theF ⁺ decays may be important in relative value (if one relies on the present estimate of theF ⁺ lifetime), the small fraction (less than 1%) obtained in theD ⁺ case, where only the annihilation mechanism can be advocated, is in agreement with what one expects for a Cabibbo suppressed decay, and disfavors a special quantitative enhancement due to this particular mechanism.     

Testing factorization of charmonium production

Within the NRQCD factorization approach the production of heavy quarkonia can be calculated in perturbative QCD in terms of a few production-process-independent NRQCD matrix elements. We test the universality of these long-distance matrix elements by comparing their values as determined from charmonium production at , ep, and colliders, and in , , and B decays. Received: 27 April 1998 / Published online: 22 March 1999     

Momentum-dependent effects in the decays of charmonium and upsilon

Decay widths of quarkonia are determined in a calculation in which the momentum distribution resulting from the localization of the quarks is taken into account. The e⁺e⁻ decay modes of charmonium and upsilon are considered with the momentum-dependent corrections to the well-known van Royen-Weisskopf formula for leptonic widths. The momentum-dependent effects are found to be significant, and amount to approximately a 20% correction. The γη(1440) decay mode is also examined to investigate a decay involving a propagating quark in the bound state. Here the momentum-dependent corrections to the static approximation are very large and suppress the decay widths by well over a factor of 3. Therefore one must exercise caution in using a static approximation.     

Experimental review of charmonium spectroscopy

Charmonium spectroscopy is one of the best means of making precision study of QCD, the strong-interaction component of the Standard Model of particle physics. Recent progress in the study of charmonium, the need for additional precision data, and the opportunities that the new facilities offer, are discussed.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.38.Qk Quantum chromodynamics: Experimental tests - 12.39.Pn Potential models - 13.25.Gv Decays of , , and other quarkonia - 14.40.Gx Mesons with S = C = B = 0, GeV (including quarkonia)