Currently, the long-standing issue concerning the size of the gluonic content of the eta' and eta mesons remains unsettled. With this in mind we consider the central exclusive production (CEP) of eta', eta meson pairs in the perturbative regime, applying the Durham pQCD-based model of CEP and the `hard exclusive' formalism to evaluate the meson production subprocess. We calculate for the first time the relevant parton-level processes gg --> qqbar gg and gg --> gggg, where the final-state gg and qqbar pairs form a pseudoscalar flavour-singlet state. We observe that these amplitudes display some non-trivial and interesting theoretical properties, and we comment on how this can be understood in a MHV framework. Finally, we present a phenomenological study, and show that the cross sections for the CEP of eta', eta meson pairs are strongly sensitive to the size of the gluon content of these mesons. The observation of these processes could therefore provide important and novel insight into this problem.
We review the theory and phenomenology of the axial U(1) problem with emphasis on the role of gluonic degrees of freedom in eta and eta' production processes, especially the low-energy pN -> pN eta and pN -> pN eta' reactions.
Gluonic degrees of freedom play an important role in the masses of the eta and etaprime mesons. We discuss eta- and etaprime-nucleon and nucleus interactions where this glue may be manifest. Interesting processes being studied in experiments are etaprime production in proton-nucleon collisions close to threshold and possible eta-nucleus bound-states.
We review the theory and phenomenology of the axial U(1) problem with emphasis on the role of gluonic degrees of freedom in the low-energy pp -> pp eta and pp -> pp eta' reactions.
We present a calculation of the process B --> D eta' within a heavy-light chiral quark model. We assume that the eta' has a large gluonic component, and its coupling is described via the glue-glue-eta' effective vertex. The main contribution comes from the non-factorizable part of the effective weak Lagrangian at quark level. We find, within our model-dependent assumptions, a branching ratio Br(B --> D eta') = (1.7 -- 3.3) 10^(-4), somewhat below the experimental upper bound 9.4 10^(-4).
The inclusive and exclusive B decays into the eta' meson plus others are investigated in a model based on the QCD anomaly. The invariant mass distribution is discussed. The constraint of the effective coupling is obtained from the data of the exclusive decay modes. The branching ratio of J/psi -> eta'eta gamma is predicted to be as large as 5.4*10^{-5}, which can be tested in the forthcoming CLEO-c experiments.
The eta(1760) may be significantly produced in J/Psi radiative decay. We deduce from experimental data that its branching ratio to two gluons is bounded, 0.4 +- 0.3 < BR(eta(1760) -> gg) < 0.9 +- 0.3, consistent with gluonic admixture. Moreover, the expectation that there should be an isoscalar analogue of the gluonic (hybrid) meson candidate pi(1800) is argued to reinforce hybrid admixture in eta(1760). Two-gluon coupling of hybrids is estimated in a spectator model to be considerably larger than that of quarkonium. In addition, the two-photon coupling of eta(1760) is estimated to be 1.4 +- 0…
We present the results of recent work on the central exclusive production of meson pairs. We concentrate on the case of flavour-singlet pseudoscalar mesons eta, eta' and show that the central exclusive process, as modelled using a recent novel application of the 'hard exclusive' perturbative formalism, is potentially highly sensitive to the size of the gluon content of these states. We also discuss the exclusive production of meson pairs in the lower mass region, and present the first results of the new Dime Monte Carlo.
The observed inclusive decay of B-mesons into eta' + X is interpreted as the consequence of the gluonic decay of the b-quark into an s-quark. As a result of the QCD anomaly this decay proceeds partly as the decay b ---> s + eta', similar to b ---> s + J/psi. The hadronic recoiling system is found to have a relatively large mass. Analogously one expects a decay of the type b ---> s + sigma. The branching ratios for these decays are large (of the order of 10%). The results indicate that there is no room for an anomalously large chromomagnetic decay mode of the b-quark. Gluon jets are expected to…
We summarize what is known about the transverse spatial distribution of gluons in the nucleon and its x-dependence from exclusive J/psi photo/electroproduction in e-p fixed-target and collider experiments (HERA H1 and ZEUS). This information can be used to predict the impact parameter dependence of the cross section for certain hard QCD processes (dijet production) in pbar-p and p-p collisions at the Tevatron and LHC.
The $η$-$η^\prime$ pseudoscalar mixing angle and the gluonium content of the $η^\prime$ meson are deduced from an updated phenomenological analysis of $J/ψ$ decays into a vector and a pseudoscalar meson. The values for the mixing angle and the gluonic content of the $η^\prime$ wave function are $ϕ_P=(44.5\pm 4.3)^\circ$ and $Z^2_{η^\prime}=0.28\pm 0.21$, respectively.
The formalism for treating the leading-twist contributions of the two-gluon Fock components occurring in hard exclusive processes that involve eta and eta' mesons is reviewed. The calculation of the eta, eta'--photon transition form factor in next-to-leading order in alpha_s, as well as, the analysis of the g* g* eta' vertex and the electro- and photoproduction of eta, eta' mesons are presented. Applications of this formalism to other relevant quantities such as glueballs are also discussed.
I briefly review the formalism for treating the leading-twist two-gluon states appearing in processes which involve eta and eta' mesons. The constraints on the size of the lowest order Gegenbauer coefficients of the two-gluon distribution amplitude are obtained from the fit to the eta and eta' transition form factor data. The results are applied to chi -> eta eta (eta' eta') decays and deeply virtual electroproduction of eta and eta' mesons.
Gluonic degrees of freedom induce a contact term in the effective chiral Lagrangian description of the low-energy pp -> pp eta' reaction. The strength of this contact term is, in part, related to the amount of spin carried by polarised gluons in a polarised proton.
We propose a mechanism which can explain the large BR(B-> X_s eta')~ 10^(-3) observed by CLEO. In this mechanism, eta' is produced by the fusion of two gluons, one from QCD penguin b->sg and the other one emitted by the light quark inside the B meson. The inclusive decay rate which is calculated via using the factorization assumption, can easily account for the observed branching ratio. We also estimate the exclusive branching ratio BR(B->K eta')=7.0X10^(-5) which is in good agreement with the experimental data and present our prediction for K* mode BR(B->K* eta')=3.4X10^(-5).
We report on some interesting recent theoretical and experimental advances on J^PC exotics and hybrid mesons. These are the decay selection rules governing J^PC exotic decay, the experimental evidence for a J^PC = 1^-+ exotic in eta pi and rho pi, and the production of charmonium hybrids at forthcoming B-factories.
We discuss exclusive central production of Higgs boson, quark-antiquark and digluon dijets. Several differential distributions are shown and disussed. Irreducible leading-order $b \bar b $ background to Higgs production is calculated in several kinematical variables. The signal-to-background ratio is shown and several improvements are suggested by imposing cuts on $b$ ($\bar b$) transverse momenta and rapidities. \
Relying on the collinear factorization approach, we demonstrate that H1 and ZEUS measurements of exclusive light vector meson and photon electroproduction cross sections can be simultaneously described for photon virtualities of $Q >2 GeV$. Our findings reveal that quark exchanges are important in this small $x_{Bj}$ region and that in leading order approximation the gluonic skewness ratio is much smaller than one.
We examine, as a correction to the central exclusive Higgs boson production in $pp$ collisions at the LHC, the rescattering of gluonic ladders off the proton. As usual, at the lowest order the hard part of this process can be described as a fusion of two hard gluonic ladders. We calculate corrections to this hard amplitude which are due to rescattering of these ladders. These corrections, which contain high mass diffractive excitations of the proton, have not yet been taken into account by the usual soft survival probabilities. We find that the correction due to the exchange of a single hard r…
We discuss the recent observation of f_0(980) in charmless B-decays and in gluon jets which hints toward a gluonic coupling of this meson similar to eta'. Further predictions on B-decays into scalar particles are presented. Charmless B decays also show a broad K Kbar (and possibly pi pi) S-wave enhancement which we relate to the 0^{++} glueball. These gluonic mesons represent a sizable fraction of the theoretically derived decay rate for b -> sg.
We investigate the exclusive production of the pseudoscalar mesons pi0, eta, eta', K+ and of the vector mesons omega, phi in a microscopic gluon-exchange or instanton model. We describe the baryons as covariant quark - scalar diquark systems with harmonic confinement, thus taking into account center-of-mass corrections and Lorentz contraction in different frames. The excitation of intermediate baryon resonances is accounted by colorless 2-gluon (soft Pomeron) exchange. We find that our model accounts for the systematics of the high precision data on exclusive meson production from various mode…
Probing the $\bar ss$ content of the $η$ and $η'$ mesons and considering mixing between these states as well as gluonic contributions, the form factors responsible for semileptonic $D_s \to (η, η') l ν$ transitions are calculated via light cone QCD sum rules. Corresponding branching fractions and their ratio for different mixing angles are also obtained. Our results are in a good consistency with experimental data as well as predictions of other nonperturbative approaches.
Given a resonance of known mass, width, and J^{PC}, we can determine its gluonic branching fraction, b(R->gg), from data on its production in radiative vector quarkonium decay, V -> gamma+R. For most resonances b(R->gg) is found to be O(10%), consistent with being q-qbar states, but we find that both pseudoscalars observed in the 1440 MeV region have b(R->gg) ~ 1/2 - 1, and b(f_0^{++}->gg) ~ 1/2. As data improves, b(R->gg) should be a useful discriminator between q-qbar and gluonic states and may permit quantitative determination of the extent to which a particular resonance is a mixture of gl…
We calculate the exclusive cross sections for e^+ e^- annihilation into two charmonium states through a virtual photon. Purely electromagnetic contributions are surprisingly large, changing the cross sections by as much as 21%. The predicted cross section for J/psi + eta_c is about an order of magnitude smaller than a recent measurement by the BELLE Collaboration, although part of the discrepancy can be attributed to large relativistic corrections. The cross sections for S-wave + P-wave, P-wave + P-wave, and S-wave + D-wave charmonium states are also calculated. It may be possible to discover …
We present the results of a recent novel application of the `hard exclusive' perturbative formalism to the process gg --> MMbar at large angles, where M (Mbar) is a light meson (anti-meson). As well as discussing the important theoretical features of the relevant leading-order gg --> qqbar(gg) qqbar(gg) 6-parton amplitudes, we also comment on their phenomenological implications. In particular, we consider the central exclusive production of meson pairs at comparatively large transverse momentum k_t, which is expected to proceed via this mechanism. We show that this leads to various non-trivial…
We compute the cross section for exclusive production of a photon associated with a heavy quarkonium H of charge-conjugation parity C=+1 from e+ e- annihilation into a virtual photon at the center-of-momentum energy root-s=10.58 GeV. The NRQCD factorization formulas for the differential and total cross sections are obtained at leading order in the strong coupling and in the relative velocity of the heavy quark in the quarkonium rest frame. The predicted cross sections for the S-wave spin-singlet cases are about 80 fb and 50 fb for H = eta_c and eta_c(2S), respectively. Among P-wave spin-triple…
We discuss exclusive central production of Higgs boson, quark-antiquark and digluon dijets. Some differential distributions are shown and disussed. Irreducible leading-order $b \bar b $ background to Higgs production is calculated. The signal-to-background ratio is shown and improvements are suggested by imposing cuts on $b$ ($\bar b$) transverse momenta and rapidities. We disuss also gluonic dijet production. Here we use rather reggeon-reggeon-gluon vertices. We discuss briefly also a new mechanism of emission of gluons from different $t$-channel gluons (reggeons). The latter contribution tur…
Updated CLEO results are presented for branching ratios and four-momentum transfer q^2 dependence of exclusive charmless semileptonic B decays, where the final state hadron is either a pi, rho, omega, eta or eta'. These results have comparable accuracies with those of other experiments. We address the issue of flavor singlet couplings by limiting Gamma(B+ -> eta' l+ nu)/Γ(B+ -> eta l+ nu)> 2.5 at 90 % CL}. We also extract a value of |V_{ub}|= (4.3 +/- 0.4 +/-0.2^{+0.6}_{-0.4})x10^{-3} in one particular unquenched lattice QCD model using pi l+nu data above q^2 of 16 GeV^2.
We review the current theoretical situation with regard to the anomalously large cross section for exclusive J/psi + eta_c production in e^+ e^- annihilation, as measured by BELLE Collaboration.
Within the nonrelativistic QCD (NRQCD) factorization framework, we calculate the exclusive decay process η_b \to J/ψJ/ψto next-to-leading order in the strong coupling constant, while at leading order in charm quark relative velocity. It is found that this new contribution to the amplitude is comparable in magnitude with the previously calculated relativistic correction piece, but differs by a phase about 90^\circ. Including this new contribution will increase the previous prediction to B(η_b \to J/ψJ/ψ) substantially, thus brightening the discovery potential of this clean hadronic decay channe…
Hadronic decay modes $D^0\to(\bar K^0, \bar K^{*0})η,η'$ and $(D^+,D_s^+)\to(π^+,ρ^+)η,η'$ are studied in the generalized factorization approach. Form factors for $(D,D_s^+)\to(η,η')$ transitions are carefully evaluated by taking into account the wave function normalization of the eta and eta'. The predicted branching ratios are generally in agreement with experiment except for $D^0\to\bar K^0η', D^+\toπ^+η$ and $D_s^+\toρ^+η'$; the calculated decay rates for the first two decay modes are too small by an order of magnitude. We show that the weak decays $D^0\to K^-π^+$ and $D^+\to K^+\bar K^0$ …
A phenomenological analysis of radiative $V\to Pγ$ and $P\to Vγ$ decays is performed with the purpose of determining the gluonic content of the $η$ and $η^\prime$ wave functions. Our results show that within our model there is no evidence for a gluonium contribution in the $η$, $Z_η^2=0.00\pm 0.12$, or the $η^\prime$, $Z_{η^\prime}^2=0.04\pm 0.09$. In terms of a mixing angle description this corresponds to $ϕ_P=(41.4\pm 1.3)^\circ$ and $|ϕ_{η^\prime G}|=(12\pm 13)^\circ$. In addition, the $η$-$η^\prime$ mixing angle is found to be $ϕ_P=(41.5\pm 1.2)^\circ$ if we don't allow for a gluonium comp…
We evaluate differential distributions for exclusive scalar $f_0(1500)$ meson (glueball candidate) production. Both QCD diffractive, pion-pion meson exchange current (MEC) components as well as double-diffractive mechanism with intermediate pionic loop are calculated. The pion-pion component, which can be reliably calculated, dominates close to the threshold while the diffractive component may take over only for larger energies. At the moment only upper limit for the QCD-diffractive component can be obtained. The diffractive component is calculated based on the Khoze-Martin-Ryskin approach pro…
We explore consequences of the existence of gluonic hot spots inside the proton for coherent and incoherent exclusive vector meson production cross sections in deep inelastic scattering. By working in the dilute limit of the Color Glass Condensate framework to compute the cross sections for Gaussian hot spots of fluctuating color charges and employing a non-relativistic vector meson wave function, we are able to perform large parts of the calculation analytically. We find that the coherent cross section is sensitive to both the size of the target and the structure of the probe. The incoherent …
The $η$-$η^\prime$ pseudoscalar mixing angle and the gluonium content of the $η^\prime$ meson are deduced from an updated phenomenological analysis of $J/ψ$ decays into a vector and a pseudoscalar meson. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be $ϕ_P=(40.7\pm 2.3)^\circ$. In presence of gluonium, the values for the mixing angle and the gluonic content of the $η^\prime$ wave function are $ϕ_P=(44.6\pm 4.4)^\circ$ and $Z^2_{η^\prime}=0.29^{+0.18}_{-0.26}$, respectively. The newly reported values of $B(J/ψ\toρπ)$ by the BABAR and BES Collabora…
As a test of the color-singlet mechanism of the nonrelativistic QCD (NRQCD) factorization approach, we consider the exclusive two-quarkonium productions in electron-positron annihilation e+ e- -> eta_c + gamma and e+ e- -> J/psi + J/psi at B factories. The cross sections are computed to the next-to-leading order in alpha_s and are resummed to all orders in half the relative velocity v of the charm quark in each meson rest frame. The available theoretical prediction of the cross section for e+ e- -> J/psi + eta_c at the same level of theoretical accuracies is consistent with the available exper…
The study of the properties of pion pairs emitted in pp Central Production Experiments (CEP) shows that a) scalar and tensor mesons production dominates at increasing energies and that 2++ production is suppressed by selecting events with low four momentum transfer square -t at both proton vertices and b) pion+pion- decays of the f0(1370) meson are directly observable as an isolated peak over a vanishing background between 1.1 and 1.6 GeV in measurements at high energies and low -t. Together with the measurements of the decay branching ratios of the f0(1370) into sigma sigma, rho rho, pion pio…
We analyze B -> K H_c (where H_c = eta_c, J/psi, chi_{cJ(J=0,1)}) decays estimating nonfactorizable contributions from the light-cone sum rules (LCSR). Nonfactorizable contributions are sizable for B -> K J/psi and particularly for B -> K chi_{c1} decay. For the B decays into a (pseudo)scalar charmonia we find small nonfactorizable contributions which cannot accommodate relatively large branching ratios obtained by measurements. This specially concerns the puzzling B -> K chi_{c0} decay.
We discuss the theoretical expectations and phenomenological evidence for the lightest glueballs and the members of the meson nonet with quantum numbers J^PC=0^{++}. We reconsider the recent evidence for candidate states with masses below ~1700 MeV, but include also the results from earlier phase-shift analyses. Arguments are presented to classify the scalars f_0(980) and f_0(1500) as members of the 0^{++} nonet, with a mixing rather similar to that of the pseudoscalars eta' and eta. The S-wave states called f_0(400-1200) and f_0(1370) are considered as different signals from a single broad re…
We present an analysis of twist-2, leading order QCD amplitudes for hard exclusive leptoproduction of mesons in terms of double/nonforward parton distribution functions. After reviewing some general features of nonforward nucleon matrix elements of twist-2 QCD string operators, we propose a phenomenological model for quark and gluon nonforward distribution functions. The corresponding QCD evolution equations are solved in the leading logarithmic approximation for flavor nonsinglet distributions. We derive explicit expressions for hard exclusive pi^0, eta, and neutral vector meson production am…
Using soft-collinear effective theory we describe at leading order in 1/m_b all the semi-inclusive hadronic B -> XM decays near the endpoint, where an energetic light meson M recoils against an inclusive jet X. We also include the decays involving eta, eta' mesons that receive additional contributions from gluonic operators. The predicted branching ratios and CP asymmetries depend on fewer hadronic parameters than the corresponding two-body B decays. This makes semi-inclusive hadronic B -> XM decays a powerful probe of the potential nonperturbative nature of charming penguins as well as a usef…
Theory and phenomenology of the eta_c photo- and electroproduction is developed from the point of view of probing the odderon singularity in QCD which corresponds to the three gluon exchange mechanism. This mechanism leads to the cross-sections which are independent of W^2 for the exchange of three non-interacting gluons or exhibit increase with increasing W^2 (or 1/x) for the odderon intercept above unity. The η_c electroproduction in the three gluon exchange mechanism is shown to be entirely controlled by the transversely polarised virtual photons. The magnitude of the eta_c photoproduction …
The $eta_L(1410)$ component of the $η(1440)$ pseudoscalar has strong affinity for glue. But its mass is incompatible with lattice simulations that predict a much higher value for the $0^{-+}$ glueball. As a consequence it has been suggested that $η_L(1410)$ could signal physics beyond the Standard Model. Here we argue that if glueballs are closed gluonic fluxtubes then $η_L(1410)$ is a prime candidate for the $0^{-+}$ glueball. Furthermore, in the absence of parity violating terms its mass should be degenerate with that of the $0^{++}$ glueball. We also suggest that the decay properties of suc…
In this short note we examine the exclusive three-body B --> Lambdabar p eta' decay using a simple pole model involving a scalar intermediate resonance state. Our aim is to test the recently formulated hypothesis that charmless baryonic B decays could occur mainly in association with eta' or gamma.
We consider central exclusive production of $gg$ dijets in proton-proton (proton-antiproton) collisions at LHC and Tevatron for different intermediate and final gluon polarisations. The amplitude for the process is derived within the $k_\perp$-factorization approach (with both the standard QCD and the Lipatov's effective three-gluon verticies) and is considered in various kinematical asymptotia, in particular, in the important limit of high-$p_\perp$ jets. Compared to earlier works we include emissions of gluons from different gluonic $t$-channel lines as well as emission of quark-antiquark di…
Exclusive hadronic B-meson decays into two-body final states consisting of a light pseudoscalar or vector meson along with an eta or eta' meson are of great phenomenological interest. Their theoretical analysis involves decay mechanisms that are unique to flavor-singlet states, such as their coupling to gluons or their ``intrinsic charm'' content. These issues are studied systematically in the context of QCD factorization and the heavy-quark expansion. Theory can account for the experimental data on the B->K^{(*)} eta^{(')} branching fractions, albeit within large uncertainties.
For hadronic two-body decays of charmed mesons involving $η$ or $η'$, resonance-induced final-state interactions (FSI) that mimic the W-exchange or the W-annihilation topology can play an essential role. In particular, the decays $D^0\to\bar K^0η'$ and $D^+\toπ^+η$, which are largely suppressed in the absence of FSI, are enhanced dramatically by resonant FSI. It is stressed that the effect of resonant FSI is negligible for $ρ^+(η,η')$ final states because of the mismatch of the G parity of $ρ^+(η,η')$ and the J=0, I=1 meson resonance. We argue that a possible gluon-mediated process in which tw…
The $η$-$η^\prime$ pseudoscalar mixing angle and the gluonium content of the $η^\prime$ meson are deduced from an updated phenomenological analysis of $V\to Pγ$ and $J/ψ\to VP$ decays. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be $ϕ_P=(41.5\pm 1.2)^\circ$ from $V\to Pγ$ and $ϕ_P=(40.5\pm 2.4)^\circ$ from $J/ψ\to VP$. In presence of gluonium, the values for the mixing angle and the gluonic content of the $η^\prime$ wave function are $ϕ_P=(41.4\pm 1.3)^\circ$ and $Z^2_{η^\prime}=0.04\pm 0.09$ from $V\to Pγ$ and $ϕ_P=(44.5\pm 4.3)^\circ$ and $Z^2…
We show how exclusive vector meson production off light ions can be used to probe the spatial distribution of small-$x$ gluons in the deuteron and $^3$He wave functions. In particular, we demonstrate how short range repulsive nucleon-nucleon interactions affect the predicted coherent $J/Ψ$ production spectra. Fluctuations of the nucleon substructure are shown to have a significant effect on the incoherent cross section above $|t|\gtrsim 0.2\,\mathrm{GeV}^2$. By explicitly performing the JIMWLK evolution, we predict the $x$-dependence of coherent and incoherent cross sections in the EIC energy …
Exclusive pseudoscalar meson production in ep scattering at high energies is a direct probe for a possible "odderon" exchange in soft hadronic processes. Using a simple phenomenological ansatz for the odderon, we demonstrate how it can be separated from the contribution due to photon-photon fusion, and the relevant parameters be measured. Total cross sections and differential distributions are presented for pi0, eta, eta', and eta_c production. Results are given from both a full calculation and one using the equivalent photon approximation. The accuracy of the latter is discussed.
The composition of the eta and eta' mesons has long been a source of discussion and is of current interest with new experimental results appearing. We investigate what can be learnt from a number of different processes: V to P gamma and P to V gamma (V and P are light vector and pseudoscalar mesons respectively), P to gamma gamma, J/psi,psi' to P gamma, J/psi,psi' to P V, and chi_{c0,2} to PP. These constrain the eta-eta' mixing angle to a consistent value, phi approx 42 degrees; we find that the c cbar components are lesssim 5% in amplitude. We also find that, while the data hint at a small g…
We propose a new variable, R_j, in order to identify exclusive double-diffractive high E_T dijet production. The variable R_j is calculated using the transverse energy E_T and pseudorapidity of the jet with the largest E_T. For a purely exclusive event the value of R_j -> 1, if we were to neglect hadronisaton and the detector resolution effects. To illustrate the expected R_j-distribution we also compute exclusive three-jet production; and, moreover, include jet smearing effects. By studying the predictions as a function of the size of the rapidity interval, delta(eta), which allows for additi…
We investigate two exclusive processes, e+ e- -> eta_c + gamma and e+ e- -> J/psi + J/psi, at the center-of-momentum energy sqrt{s}=10.58 GeV within the framework of the nonrelativistic QCD factorization approach. A class of relativistic corrections is resummed to all orders in the heavy-quark velocity v and the corrections are large negative. We further improve the prediction by including available QCD next-to-leading-order corrections and the interference between the QCD and relativistic corrections. The prediction for sigma[e+ e- -> eta_c + gamma] is about 50 fb. In the case of e+ e- -> J/p…
We calculate the cross section for the exclusive production of J^{PC}=0^{++} glueballs G_0 in association with the J/psi in e^+e^- annihilation using the pQCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative Upsilon decay. The cross section for e^+e^- -> J/psi+ G_0 at sqrt{s}=10.6 GeV is similar to exclusive charmonium-pair production e^+e^- -> J/psi+h for h=eta_c and chi_{c0}, and is larger by a factor 2 than that for h=eta_{c}(2S). As the subprocesses gamma^* -> (c c-bar) (c c-bar) and gamma^…
Central exclusive production (CEP) processes in high-energy proton -- (anti)proton collisions offer a very promising framework within which to study both novel aspects of QCD and new physics signals. Among the many interesting processes that can be studied in this way, those involving the production of heavy (c,b) quarkonia and gamma gamma states have sufficiently well understood theoretical properties and sufficiently large cross sections that they can serve as `standard candle' processes with which we can benchmark predictions for new physics CEP at the CERN Large Hadron Collider. Motivated …
Mapping states with explicit gluonic degrees of freedom in the light sector is a challenge, and has led to controversies in the past. In particular, the experiments have reported two different hybrid candidates with spin-exotic signature, pi1(1400) and pi1(1600), which couple separately to eta pi and eta' pi. This picture is not compatible with recent Lattice QCD estimates for hybrid states, nor with most phenomenological models. We consider the recent partial wave analysis of the eta(') pi system by the COMPASS collaboration. We fit the extracted intensities and phases with a coupled-channel …
