Omegaprimes and glueballs

An analysis is presented of ρπ and ωππ systems ine ⁺ e ^? annihilation. Definite evidence is obtained for two ω′ states at masses of 1.39 and 1.59 GeV. Incorporating these states in an analysis of the corresponding channels in diffractive photoproduction indicates the presence of a new process in isoscalar diffractive photoproduction which is not present in the isovector case. The possible relationship to the anomalous ratio of the rates of ψ′ andJ/ψ decay to ρπ is raised: both point to the presence of one or moreJ ^pc =1^?? glueball states between 2 and 3 GeV.     

Diffractive photoproduction of the ϱ-meson

?^o photoproduction is analyzed in the framework of the Regge pole model, considering only pomeron exchange and assuming coservation of the photon helicity in the s-channel for small momentum transfer (∣t∣ < 0.3 (GeV/c)²). The main features of ?^o photoproduction are well described.     

Diffractive large transferred momentum photoproduction of vector mesons

The large t behavior of the helicity amplitudes of diffractive photoproduction is estimated relying on models of the photon and meson light-cone wave functions and on the double-logarithmic approximation to the exchanged gluon interaction. The role of large-size color dipole contributions to the photon-meson transition impact factor is discussed.Received: 17 November 2003, Revised: 10 March 2004, Published online: 23 June 2004A. Ivanov: Corresponding author.     

Diffractive dijet cross sections in photoproduction at HERA

Differential dijet cross sections have been measured with the ZEUS detector for photoproduction events in which the hadronic final state containing the jets is separated with respect to the outgoing proton direction by a large rapidity gap. The cross section has been measured as a function of the fraction of the photon () and pomeron () momentum participating in the production of the dijet system. The observed dependence shows evidence for the presence of a resolved- as well as a direct-photon component. The measured cross section increases as increases indicating that there is a sizeable contribution to dijet production from those events in which a large fraction of the pomeron momentum participates in the hard scattering. These cross sections and the ZEUS measurements of the diffractive structure function can be described by calculations based on parton densities in the pomeron which evolve according to the QCD evolution equations and include a substantial hard momentum component of gluons in the pomeron. Received: 20 April 1998 / Published online: 2 July 1998     

Diffractive photoproduction of charm at the HERA ep collider

For various kinematical domains, the cross section for the diffractive photoproduction of D* mesons at the HERA ep collider is calculated within a model based on perturbation theory. The results obtained by using different models of the Pomeron are compared.     

Diffractive photoproduction of dijets in ep collisions at HERA

Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb^-1. The measurements were made in the kinematic range Q² < 1 GeV², 0.20<y<0.85 and x_IP<0.025, where Q² is the photon virtuality, y is the inelasticity and x_IP is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy, E_T ^jet, were required to satisfy E_T ^jet>7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range -1.5<η^jet<1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive parton distributions of the proton.     

Diffractive open charm production in deep-inelastic scattering and photoproduction at HERA

Measurements are presented of diffractive open charm production at HERA. The event topology is given by ep→eXY where the system X contains at least one charmed hadron and is well separated by a large rapidity gap from a leading low-mass proton remnant system Y. Two analysis techniques are used for the cross section measurements. In the first, the charm quark is tagged by the reconstruction of a D^*±(2010) meson. This technique is used in deep-inelastic scattering (DIS) and photoproduction (γp). In the second, a method based on the displacement of tracks from the primary vertex is used to measure the open charm contribution to the inclusive diffractive cross section in DIS. The measurements are compared with next-to-leading order QCD predictions based on diffractive parton density functions previously obtained from a QCD analysis of the inclusive diffractive cross section at H1. A good agreement is observed in the full kinematic regime, which supports the validity of QCD factorization for open charm production in diffractive DIS and γp.     

Diffractive photoproduction of jets with a direct pomeron coupling at HERA

We investigate in detail the effect of a direct pomeron coupling to quarks on the production of jets inep scattering with almost real photons. Jet production via a direct pomeron coupling is compared with the resolved-pomeron mechanism. We consider both direct and resolved photoproduction. Rapidity and transverse momentum distributions are calculated and compared with preliminary H1 and ZEUS data.     

Diffractive photoproduction of D*±(2010) at HERA

Diffractive photoproduction of D^*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb^-1. The D^* mesons were reconstructed in the kinematic range: transverse momentum p_T(D^*) > 1.9 GeV and pseudorapidity |η(D^*)|<1.6, using the decay D^*+→D⁰π⁺ _s followed by D⁰→K^-π⁺(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon–proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q² < 1 GeV², in two ranges of the Pomeron fractional momentum x_IP<0.035 and x_IP<0.01. The relative contribution of diffractive events to the inclusive D^*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.     

Modified action glueballs

The mass of the 0⁺ glueball in 4-dimensional lattice gauge theory with a mixed SU(2)-SO(3) action is obtained via Monte Carlo. We work in a region far from the critical end point in the phase diagram, with an action partly motivated by renormalization group flows in the Migdal-Kadanoff approximation. A large-N resummation of perturbation theory is used to show that the mass gap scales as predicted by the perturbative renormalization group. Independent of this, our results show that the ratio of the glueball mass to the square root of the string tension, obtained from a previous Monte Carlo, is a renormalization group invariant.     

There are no classical glueballs

I show that there are no finite-energy non-singular solutions of classical Yang-Mills theory in four-dimensional Minkowski space that do not radiate energy out to spatial infinity. Finite-energy non-singular solutions that are either static or periodic in time, are a fortiori non-radiant; thus this generalizes earlier theorems that state that there are no such solutions.Research supported in part by the National Science Foundation under Grant No. PHY75-20427     

The experimental status of glueballs

Glueballs and other resonances with large gluonic components are predicted as bound states by Quantum Chromodynamics (QCD). The lightest (scalar) glueball is estimated to have a mass in the range from 1 to 2 GeV/c²; pseudoscalar and tensor glueballs are expected at higher masses. Many different experiments exploiting a large variety of production mechanisms have presented results in recent years on light mesons with J^PC=0⁺⁺, 0⁻⁺, and 2⁺⁺ quantum numbers. This review looks at the experimental status of glueballs. Good evidence exists for a scalar glueball which is mixed with nearby mesons, but a full understanding is still missing. Evidence for tensor and pseudoscalar glueballs are weak at best. Theoretical expectations of phenomenological models and QCD on the lattice are briefly discussed.     

J-- glueballs and a low odderon intercept

We report an odderon Regge trajectory emerging from a field theoretical Coulomb gauge QCD model for the odd signature J(PC) (P = C = -1) glueball states. The trajectory intercept is clearly smaller than the Pomeron and even the omega trajectory's intercept which provides an explanation for the nonobservation of the odderon in high energy scattering data. To further support this result we compare to glueball lattice data and also perform calculations with an alternative model based upon an exact Hamiltonian diagonalization for three constituent gluons.     

Constituent gluon interpretation of glueballs and gluelumps

Arguments are given that support the interpretation of the lattice QCD glueball and gluelump spectra in terms of bound states of massless constituent gluons with helicity 1. In this scheme, we show that the mass hierarchy of the currently known gluelumps and glueballs is mainly due to the number of constituent gluons and can be understood within a simple flux tube model. It is also argued that the lattice QCD 0^+- glueball should be seen as a four-gluon bound state. We finally predict the mass of the 0^- state, not yet computed in lattice QCD.     

Spotting glueballs in collinear gluon jets

We suggest looking for pure gluon hadronic states (glueballs) in ?→ 3g → low spherically final state (collinear gluon jets). In these events one gluon has the maximum energy, $\text{M?}\text{2}$, favouring fragmentation into a glueball. The signature for a true C = G + glueball is its prominence at the ? resonance in e⁺e^? →? → (glueball → four charged pions) + … and its absence in q$\text{q}$ jets off (we do not expect significant quark fragmentation into glueballs).     

Scalar mesons and glueballs in D_p-D_q hard-wall models

We investigate the light scalar mesons and glueballs in the Dp-Dq hard-wall models, including D3-Dq, D4-Dq, and D6-Dq systems. It is found that only in the D4-D6 and D4-D8 hard-wall models are the predicted masses of the qˉq scalar meson f0 scalar glueball consistent with their experimental or lattice results. This indicates that D4-D6 and D4-D8 hard-wall models are the favorite candidates of the realistic holographic QCD model.