Production of P-wave charmonium states in two-particle decays of B c mesons

On the basis of the model of hard one-gluon exchange, the two-particle hadronic decays of B _c mesons into S-and P-wave charmonium states, B _c → X _cc π(ρ), are considered at high momentum transfers and in the nonrelativistic approximation. It is shown that the width with respect to B _c-meson decay into S-wave charmonium states is two times greater than the width with respect to B _c-meson decay into P-wave states and that the yield of J/ψ mesons in the cascade processes of B _c-meson decay via the formation and radiative decay of P-wave charmonium states is approximately 8% of the yield of directly produced J/ψ mesons.     

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.     

Charmonium sum rules andη c production in two-photon reactions

The coupling of the pseudoscalar charmonium stateη _c to two photons is calculated using the charmonium sum rules. The resulting value of the two-photon decay width is Λ=5.6 KeV (±10%). If the virtualness of one of the photons is increased from |k ₁ ² |=0 to |k ₁ ² |=1 GeV² the coupling decreases about 10%.     

Sum rules for the decays of the c-even charmonium states

Sum rules for the decays of the C-even charmonium levels (¹S₀, ³P₀, ³P₂, ¹D₂) are derived. These rules are based on the asymptotic freedom of the quantum chromodynamics at small distances and on the analyticity. They refer to the various vacuum amplitudes involving products of charmed quark currents: electromagnetic current as well as currents with quantum numbers J^PC=0^?+,0⁺⁺,2⁺⁺,2^?+. The contribution of the continuum to some of the sum rules is small, and they are saturated by the contribution of the lowest charmonium levels. In this way we predict the widths of the two-photon decays of the charmonium states and estimate their total hadronic widths.     

Masses of lowest lying heavy mesons in QCD

Using QCD sum rules for the polarization operator ∏^J(Q²) induced by all possible currents with J^PC=0^??, 1^??, 0⁺⁺, 1⁺⁺ and 2⁺⁺ we calculate the S- and P-states of charmonium. Power corrections due to the gluon condensate operator G^α_μνG^α_μν are included and shown to be very important. All known lowest lying charmonium states are reproduced extremely well and a firm prediction is made for the ¹P₁ state.     

QCD sum rules for heavy quark systems

In this paper we present in a detailed and coherent fashion our work on QCD sum rules for equal mass heavy quark meson states. We discuss the technical procedures used to calculate the perturbative and non-perturbative contributions to the vacuum polarization, which have been calculated for all currents up to and including spin 2⁺⁺. Using dispersion relations, sum rules are derived. Extensive applications are made to the lowest lying states of the charmonium and upsilon systems. The masses of the S- and P-wave charmonium levels are reproduced to a high degree of accuracy, and the mass of the ¹P₁ level is predicted at 3.51 GeV. For the upsilon system it only appears to be possible to predict the γ-η_b splitting which gives 60 MeV. Very accurate values are given for the current quark masses at p² = ?m_q²: m_c = 1.28 GeV and m_b = 4.25 GeV.     

Enhancement of heavy quarkonium production in hadron collisions at finite temperature

We estimate how the masses and wave functions of heavy quarkonium mesons change with temperature below the deconfining temperatureT _c . To do so we use simple, theoretically motivated parametrizations of the way the heavy quark potential and quark masses vary with temperature. The effect of these changes on the production of charmonium and bottonium in hadron-hadron collisions is estimated using a standard phenomenological model. We find, for example, that forT close toT _c enhancements by as much as a factor of 3 are possible for charmonium and bottonium highp _T production at SPS energies \(\sqrt s\) =20 GeV. Thep _T and energy dependence of this enhancement is non-trivial. We discuss the relevance of our results for the interpretation of recentJ/ψ data from heavy ion collisions.     

The ψ′-η′c hyperfine splitting

The hyperfine splitting of the radially excited states ψ′ and η′_c is studied within the framework of potential models. Some rigorous results are derived and some phenomenological approaches are commented on. The recent experimental result M(ψ′)?M(η′_c) = 93 MeV favours very short-range spin-spin forces and seems, on the other hand, difficult to accommodate if there is a sizeable effect of virtual D meson pairs on the charmonium mass spectrum.     

Charmonium States in QCD-Inspired Quark Potential Model Using Gaussian Expansion Method

We investigate the mass spectrum and electromagnetic processes of charmonium system with the nonperturbative treatment for the spin-dependent potentials, comparing the pure scalar and scalar-vector mixing linear confining potentials. It is revealed that the scalar-vector mixing confinement would be important for reproducing the mass spectrum and decay widths, and therein the vector component is predicted to be around 22?%. With the state wave functions obtained via the full-potential Hamiltonian, the long-standing discrepancy in M1 radiative transitions of J/ψ and ψ′ are alleviated. This work also provides an inspection and suggestion for the possible cc? states among the copious higher charmonium-like states. Particularly, the newly observed X(4160) and X(4350) are found in the charmonium family mass spectrum as M(2¹ D ₂)?= 4164.9 MeV and M(3³ P ₂)?= 4352.4 MeV, which strongly favor the J ^PC ?=?2^?+, 2⁺⁺ assignments respectively. The corresponding radiative transitions, leptonic and two-photon decay widths have been also predicted theoretically for the further experimental search.     

ηc as we know it

Various theoretical models for paracharmonium are critically reviewed. The main emphasis is put on the dispersion approach which has proved to be powerful enough to fix, say, the η _c mass,m _ηc =(3.00±0.02) GeV. A few original remarks concerning mainly the radiative transitions in charmonium are included. In particular, a new, simple, and reliable method for calculatingΓ(J/ψ→η _c γ) is described which makes no reference to potentials, overlap integrals, etc.     

Vacuum insertion and nonperturbative effects for exclusive nonleptonic decays of charmed mesons and kaons

We re-examine QCD sum rules forS-wave charmonium. Dimension 6, 8 contributions for both³ S ₁,¹ S ₀ waves are taken into account using the factorisation model and found to be reasonably small. A good fit to the data requires the confinement parameterφto be much bigger than the generally accepted value.     

Bound states of heavy quarks on the light plane

We investigate in detail the light plane formulation of bound state equations and of the interactions of bound states. This formalism is particularly well suited to discuss bound states of heavy quarks since these states can be well approximated as two particle states but yet there are significant relativistic corrections to the conventional nonrelativistic approach. Applications are made to electromagnetic decays of charmonium (ψ→e ⁺ e ^?, η _c →γγ, ψ′→η _c γ, etc.).     

Suppression of charmonium production in PbPb collisions at 158 GeV/c per nucleon and quark-gluon deconfinement

An anomalous suppression of the charmonium yield in central collisions was observed in studying charmonium production in collisions of Pb nuclei accelerated to a momentum of 158 GeV/c per nucleon with Pb target nuclei. It is shown that, in peripheral collisions, the ratio of the cross section for J/ψ production to the cross section for the Drell-Yan process decreases exponentially (as in the case of collisions of lighter nuclei) owing to the ordinary absorption of J/gy in nuclear matter. The observed threshold effect of the anomalous suppression of charmonium production agrees well with the predictions based on the assumption of Debye color screening in the formation of quark-gluon plasma.     

A study of the charmonium,upsilon and strangeonium systems

We study the charmonium, upsilon and strangeonium systems with a linear+Coulomb potential, in the high α _s regime. Our approach is based on the Bethe-Salpeter equation, in ladder approximation, and the most interesting conclusion of our work seems to be that it is not possible to fit these three families of mesons using the same set of values for the parameters defining the potential.     

Measurement of the 85Rb(γ, n)84mRb cross-section in the energy range 10-19 MeV with bremsstrahlung photons

We study the charmonium 2S states ??? and ??? _c , and the bottomonium 2S states ???? and ??? _b , using the light-front quark model and the 2S state wave function of harmonic oscillator as the approximation of the 2S quarkonium wave function. The decay constants, transition form factors and masses of these mesons are calculated and compared with experimental data. Predictions of quantities such as Br(???????? _c ) are made. The 2S wave function may help us learn more about the structure of these heavy quarkonia.     

Color screening and deconfinement for bound states of heavy quarks

We study the binding and deconfinement of heavy quarks in a thermal environment, using a non-relativistic confinement potential model with color screening. As a result, we obtain the dependence of the dissociation energies, the binding radii and the masses of heavy quark resonances (charmonium and bottonium states) on the color screening lengthr _D of the medium, and we determine for the different resonances those values ofr _D below which no more binding is possible. Finally, we consider the implication of our results on resonance suppression as signal for deconfinement.     

Hadronic collisions: A quarkonium factory

Hadronic collisions are quite efficient in producing new quark flavours due to the large gluon content of ordinary hadrons. In particular, one may expect sizable yields of heavy quark-antiquark bound states with various spin and orbital quantum numbers. Using perturbative QCD in combination with the nonrelativistic quarkonium model we present a fairly complete and detailed picture of charmonium and bottomonium production. We compare our results on inclusiveJ/ψ and γ distributions with high energypp data and make predictions onη _c and χ production.     

Penguins,trees and final state interactions in B decays in broken SU3

The availability of data on B_s decays to strange quasi-two-body final states, either with or without charmonium opens new possibilities for understanding different contributions of weak diagrams and in particular the relative contributions of tree and penguin diagrams. Corresponding B_d and B_s decays to charge conjugate final states are equal in the SU(3) symmetry limit and the dominant SU(3) breaking mechanism is given by ratios of CKM matrix elements. Final State Interactions effects should be small, because strong interactions conserve C and should tend to cancel in ratios between charge conjugate states. Particularly interesting implications of decays into final states containing η and η′ are discussed.     

Charmonium production in hadronic experiments at an energy of 70 GeV

The production of charmonium states in hadronic experiments is considered in the third order in the strong-coupling constant. It is shown that some significant difficulties that arise if such reactions are treated in the leading order can be overcome within this approach. In particular, the method applied here makes it possible to obtain transverse-momentum distributions of final-state charmonia. Also, the experimental observation of a χ _c1 meson, which cannot be produced in the lowest order in α _s , is then explained in a natural way.     

Hadrinoc production of χ c -nesons at LHC

Hadronic production of P-wave charmonium states χ _cJ in hadronic interaction is considered. Using the experimental results of CDF and LHCb collaborations, we show, that contributions of color singlet components are dominant. As for the color octet mechanism, then we show, that contributions from P-wave states can also be observed, while the contribution from S-wave is negligible. The best experimental observables that give information about relative importance of color-singlet and color-octet components are the ratios χ _c2/χ _c1 and χ _c 0/χ _c1.