Near-threshold <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis>-meson photoproduction on nuclei

On the basis of the first-collision model that relies on the nuclear spectral function and which includes incoherent processes involving charmonium production in proton–nucleon collisions, the photoproduction of J/ψ mesons on nuclei is considered at energies close to the threshold for their production on a nucleon. The absorption of final J/ψ mesons, their formation length, and the binding and Fermi motion of target nucleons are taken into account in this model along with the effect of the nuclear potential on these processes. The A dependences of the absolute and relative charmonium yields are calculated together with absolute and relative excitation functions under various assumptions on the magnitude of the cross section for J/ψN absorption, the J/ψ-meson formation length, and their inmedium modification. It is shown that, at energies above the threshold, these features are virtually independent of the formation length and the change in the J/ψ-meson mass in nuclear matter but are rather highly sensitive to the cross section for J/ψN interaction. The calculations performed in the present study can be used to determine the unknown cross section for J/ψ-meson absorption in nuclei from a comparison of their results with data expected from experiments in the Hall C of the CEBAF (USA) facility upgraded to the energy of 12 GeV. It is also shown that the absolute and relative excitation functions for J/ψ mesons in photon–nucleus reactions at subthreshold energies are sensitive to the change in the meson mass and, hence, carry information about the properties of charmonium in nuclear matter.     

<Emphasis Type="Italic">B</Emphasis>-meson decays into charmonium states in the ATLAS experiment

The paper presents several recent ATLAS results on the analyses of B-meson decays into charmonium states. These include the measurements of B⁺ mass and the fractions of J/ψ mesons produced in b-hadron decays in pp collisions at \(\sqrt s\) = 13 TeV in the center of mass system. The measured partial widths and polarizations in B _c ⁺ → J/ψD _s ^(*)+ decays and CP-violation parameters in B _s ⁰ → J/ψ? decays in pp collisions at 7 and 8 TeV in the center of mass system are also presented.     

Charmonium production in proton-proton collisions and in collisions of lead nuclei at CERN and comparison with Brookhaven data

A review of experimental data on charmoniumproduction that were obtained in fixed-target experiments at the SPS synchrotron and in proton-proton collisions and in collisions of lead nuclei in beams of the Large Hadron Collider (LHC) at CERN (Switzerland) is presented. A comparison with data obtained at the Brookhaven National Laboratory (USA) from experiments at the Relativistic Heavy Ion Collider (RHIC) is performed. Measurement of the suppression of J/ψ-meson production as a possible signal of the production of quark-gluon plasmawas proposed back in 1986 by T. Matsui and H. Satz. An anomalous suppression of J/ψ-meson production was discovered by the NA50 Collaboration at SPS (CERN) in central collisions of lead nuclei at the c.m. collision energy of 158 GeV per nucleon. Data obtained at the c.m. energy of 200 GeV per nucleon in the PHENIX experiment at RHIC indicate that, depending on multiplicity, the suppression of J/ψ-meson production at this energy approximately corresponds to the suppression of J/ψ-meson production in collisions of lead nuclei at the SPS accelerator. Theoretical models that take into account the regeneration of J/ψ mesons describe better RHIC experimental data. The measurement of charmonium production in proton-proton collisions and in collisions of lead nuclei in LHC beams revealed the importance of taking into account the regeneration process. At the LHC energies, it is also necessary to take into account the contribution of B-meson decays. Future measurements of charmonium production at the LHC to a higher statistical precision and over an extended energy region would be of importance for obtaining deeper insight into the mechanism of charmonium production and for studying the properties of matter at high energy density and temperature.     

Q1(1290) and Q2 (1400) decay rates and their SU(3) implications

We summarize and combine the known information on the decay rates of the strangeness-one axial vector mesons, Q₁ and Q₂. From this information and the rate for B→ωπ, we determine the Q_A?Q_B mixing angle and the S-wave, symmetric and antisymmetric octet couplings for vector-pseudoscalar decays of axial vector mesons. If we assume the D(1285) and the E(1420) belong to the J^PC=1⁺⁺ nonet, we find the A₁ to have a mass of ～1.47 GeV and a large (>0.3 GeV) width.     

Tevatron and LHC potential for observing <Emphasis Type="Italic">χ</Emphasis><Subscript>b</Subscript>

Results of recent studies that indicate that allowance for the relative motion of quarks in mesons leads to an increase in the cross sections for the process e ⁺ e ^? → J/ψη _c are confirmed. It is shown that the same effect also leads to an increase in the width of scalar and tensor mesons with respect to their decay to two vector mesons, so that the decays χ _b0,2 → 2J/ψ can be used to observe these mesons at the Tevatron collider and LHC.     

The puzzle of the D and D<Subscript>s</Subscript> mesons

We present a theoretical framework that accounts for the new D_J and D_sJ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional P-wave quark-antiquark states and four-quark components. The narrowest states are basically P-wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold. We study the electromagnetic decay widths as basic tools to scrutiny their nature.     

Charmonium production inB-decays

We calculate partial widths for the decay of theB-meson into all possible charmonium states and estimate the corresponding branching ratios.     

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.     

Decay constant ratios ƒ ηc/ƒ J/ψ and ƒ ηb/ƒ ψ

We calculate the decay constant ratios ? _ηc/? _J/ψ and ? _ηb/? _ψ. In the calculation we take into account the mock meson structures of the mesons, as well as the difference of the wave functions at origin of the vector and pseudoscalar mesons studied by Ahmady and Mendel. We find that the different spin structures of the mesons much affect the ratios. We incorporate our results in the prediction of the branching ratios of B → K η _c.     

Electromagnetic transition form factors of light vector mesons

The decays of narrow light vector mesons into pseudoscalar mesons and dileptons are calculated to leading order in a recently proposed scheme which treats pseudoscalar and vector mesons on equal footing. Since all required parameters have been determined by other reactions the presented approach gains predictive power for the considered processes. The decay of the ω-meson into pion and dimuon agrees reasonably well with the available experimental data concerning form factor, single-differential decay width and partial decay width. As well do the partial decay width of the ω-meson into a pion and a dielectron and of the ?-meson into an η-meson and a dielectron. The decay properties of the ω-meson into η-meson and dimuon or dielectron and of the ?-meson into η-meson and dimuon are predicted.     

The radial excitations of η−η′ mesons

The possibility of identification of a number of the recently discoveredJ ^PC=0^?+ isosinglet resonances (the ζ(1275), ι(1460) and others) as radial excitations of the η(549)- and η′(958)-mesons is investigated within the earlier developed phenomenological approach to analyse radial excitations of light mesons. The widths of the electromagnetic and strong decays of these mesons and the branching ratios of their production in the radiativeJ/ψ decay, as well as in the π^- p charge exchange reaction, are estimated. It is pointed out that the abundant production of the ι-meson in theJ/ψ-decays and the small width of the ι→2γ decay put forward repeatedly as an evidence for the glueball nature of this meson, can qualitatively be obtained in one of the considered schemes of the radial excitations of the η?η′-system.     

Hadronic production ofS- andP-wave states of\bar b-quarkonium-quarkonium

In the leadingO(α _s ⁴ ) order of the perturbative QCD, the hadronic production cross-sections ofS- andP-wave states ofB _c meson are calculated. The results for theS-wave levels are compared with the values given in other papers as well as in the model of thebquark fragmentation intoB _c . In the given order, the cross-sections of the hadronic production of theP-wave states are calculated for the first time. Their contribution into theB _c meson production is less than 10%. There is a strong difference between the predictions of the fragmentation model and the exact perturbative calculations. These differences are discussed in details for the differential distributions over various kinematical quantities.     

A string-breaking model of heavy meson decays

Within QCD, heavy quarkonia are viewed as a quark antiquark pair bound by a narrow chromoelectric flux tube. This flux can create light quark antiquark pairs accounting for the decay into mesons with heavy quantum numbers. This model is shown to be as consistent with current data on charmonium decays intoD-meson pairs and upsilon decay to \(B\bar B\) , as is the physically less appealing³ P ₀ model.     

Spin effects in two-body hadronic decays of the B c mesons

Spin effects in the weak two-body hadronic decays of the B _c and B _c ^* mesons into J/ψ and ρ(π) mesons are considered within the model of hard one-gluon exchange between quarks at high momentum transfers. It is shown that the polarization of the J/ψ meson in the decays of the B _c ^* meson differs substantially from that in the decays of the B _c ^* meson. The decay widths of the B _c ^* meson differ significantly from the widths of the B _c ^* meson.     

Meson-photon transition form factors and resonance cross-sections in e+e− collisions

Meson-photon-photon transition form factors for S-, P-, and D-wave states are calculated, the meson being treated as a non-relativistic heavy-quark-antiquark pair. The full dependence on both photon virtualities is included. Cross-section formulas for charge-conjugation even mesons with J^p = 0⁻, 0⁺, 1⁺, 2⁺, and 2⁻ in electron-positron collisions are presented and numerical results for LEP energies are given. In particular, we find two-photon event rates for χ_c1, η_c(2S), and η_b(1S) within reach of LEP.With minor modifications to incorporate SU(3)-flavour breaking we estimate rates for 18 light mesons as well, based on the observation that their two-photon decay widths agree remarkably well with measured data. Finally we point out that e⁺e⁻ cross sections for 1⁺ states do not vanish at low Q², the Landau-Yang suppression factors of the two-photon cross sections being compensated by the photon propagators.     

(η−η′−ι)-mixing,decay and production mechanisms

We present a phenomenological model for meson-glueball mixing and apply it to the mixing of the pseudoscalar mesons η and η′ with the ι(1440)-particle as the prime candidate for a 0^?+-glueball. Using the MIT bag model framework, our model incorporates, among other elements, configuration mixing effects due to virtually excited states, as well as mixing of quark and gluon components. We evaluate the portions of quark antiquark and two-gluon admixtures in η,η′ and ι. The results are used to study various decay and production processes involving these particles. In particular, we calculate the radiative and the 2γ-decay widths of the light mesons and make predictions for the widths of the ι in these channels. Furthermore, production mechanisms of the light mesons in electromagnetic and hadronicJ/ψ-decays are used to evaluate the branching ratios for the production of the ι in variousJ/ψ-transitions. Our results are generally in reasonable agreement with experimental data. Especially we predict a rather large width for the decay ι→ργ and a sizable production rate for the ι in the transitionJ/ψ→ωι.     

Double P-wave charmonium production in e + e − annihilation

On the basis of perturbative QCD and relativistic quark model we calculate relativistic and bound state corrections in the production processes of a pair of \(\mathcal{P}\) -wave charmonium states. Relativistic factors in the production amplitude are taken into account connected with the relative motion of heavy quarks and the transformation law of the bound-state wave function to the reference frame of the moving \(\mathcal{P}\) -wave mesons. Relativistic corrections to the quark bound-state wave functions in the rest frame are considered by means of the Breit-like potential. It turns out that the examined effects change essentially nonrelativistic results of the cross section for the reaction e ⁺ + e ^? → h _c + χ _c J at the center-of-mass energy √s = 10.6 GeV.     

The forgotten 1D2 level of charmonium

The standard “charmonium” picture predicts four C=+1 states (³P₀, ³P₁, ³P₂, 2 ¹S₀) between ψ and ψ′. If these are identified with the four experimentally observed levels, serious difficulties arise. We remark that a ,,forgotten” ¹D₂ level (J^PC=2^?) is likely to be around 3.5 GeV. It may be identified with χ(2.45) or χ(3.50), avoiding the above above difficulties. The 2 ¹S₀ level has then yet to be discovered.     

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.     

Estimating of CP-violation in <Emphasis Type="Italic">B</Emphasis><Superscript>0</Superscript>→ψ(2<Emphasis Type="Italic">S</Emphasis>)π<Superscript>0</Superscript> decay

I present estimates of CP-violating asymmetries in the non-leptonic charmonium two-body B⁰→ψ(2S)π⁰ decay and the same decays of B⁺→ψ(2S)π⁺ and B⁺→ψ(2S)K⁺ These estimates are based on QCD and improved QCD factorization approach making use of next-to-leading order (NLO) contributions. The CP-violating asymmetry for B⁰→ψ(2S)π⁰ decay is not available, according to the same calculations, it is expected if it can be measured in the future its value will be S_ψ(2S)π0(B⁰ → ψ(2S)π⁰)= 0.662 ± 0.197 and C_ψ(2S)π0(B⁰ → ψ(2S)π⁰)= 0.024 ± 0.007.