The problem of radial excitations of light mesons

Strong decays of the ground and radial-excited (L=0) states of light mesons are calculated within a relativistic (Lorentz-contraction-modified) version of the model of spontaneous production of aq \(\bar q\) -pair from vacuum.     

Pseudoscalar mesons and their radial excitations from the effective chiral Lagrangian

The effective chiral Lagrangian is derived from QCD in the framework of the field correlator method. It contains the effects of both confinement and chiral symmetry breaking due to a special structure of the resulting quark mass operator. It is shown that this Lagrangian describes light pseudoscalar mesons, and Gell-Mann-Oakes-Renner relations for pions, eta and K mesons are reproduced. The spectrum of radial excitations of pions and K mesons is found and compared to experimentally known masses.     

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.     

The problem of radial excitations of light mesons and interpretation of the iota-meson

Radial (L=0) excitations of light (including strange) mesons are considered in the framework of the quark phenomenological model. The predicted spectrum of excitations is compared with experimentally observed resonances. The dependence of energy levels on quark masses is pointed out which explains the nearness of ρ (1600) and ? (1680) resonances. The possibility of interpreting the τ (1440)-resonance as a radial excitation of η (549) and η′ (958) mesons is analysed. The position of now unobserved states is calculated and proposed for the experimental check of the spectrum of radial excitations of light mesons.     

Observation of the tensor glueball

In the reactions p-p → π ⁰ π ⁰, ηη, ηη′, in the mass region 1900–2400 MeV there are four relatively narrow resonances f ₂(1920), f ₂(2020), f ₂(2240), and f ₂(2300) and a broad one f ₂(2000). In the framework of quark combinatorics, we carry out an analysis of the decay constants for all five resonances. It is shown that the relations for the decay constants corresponding to the broad resonance f ₂(2000) → π ⁰ π ⁰, ηη, ηη′ are the same as those corresponding to a glueball. An additional argument in favor of the glueball nature of f ₂(2000) is the fact that f ₂(1920), f ₂(2020), f ₂(2240), and f ₂(2300) fit well the q-q trajectories in the (n, M ²) plane (where n is the radial quantum number), while the broad f ₂(2000) resonance turns out to be an unnecessary extra state for these trajectories. The text was submitted by the authors in English.     

Meson decays of the glueball

We estimate the decay widths of the 0^±-glueballs by taking account of the mixings with η and η′ through their anomalous coupling. We find a pseudoscalar glueball with a broad decay width, if its mass is larger than m_δ(980) + m_π. On the other hand, a scalar glueball has a narrow decay width. Assuming E(1440) to be the pseudoscalar glueball, we predict Γ_δ(980)ππ≈ 40 MeV.     

QCD sum rules and radial excitations of light pseudoscalar and scalar mesons

The calculations of masses and decay constants of the radial excitations of light pseudoscalar and scalar mesons within the QCD sum rules method are briefly reviewed. The predictions are based on the 1/N _c -supported model spectra, which consist of an infinite number of infinitely narrow resonances, and on the assumption that the ground states of light scalar mesons may be considered as \(\bar qq\)-bound states. The results of the studies are compared with the existing experimental data and with the predictions of other theoretical approaches.     

First identification of collective excitations in127Ce

Collective bands have been identified for the first time in the nucleus¹²⁷Ce using in- beam spectroscopic techniques. A band developed up to spin 51/2 is proposed to be based on an h_11/2 neutron hole configuration. The observed backbend is produced by the alignment of an h_11/2 proton pair. Another level sequence is very likely generated by ag_7/2 or d_5/2 neutron- hole.     

Towards resolution of the scalar meson nonet enigma

By the application of a linear mass spectrum to a composite system of both the pseudoscalar and scalar meson nonets, we find three relations for the masses of the scalar states which suggest the assignment for the scalar meson nonet a₀(1320), K ₀ ^* (1430), f₀(1500), and f₀ ^′(980).     

Observation of the lightest scalar glueball

The (IJ ^PC = 00⁺⁺)-wave is analysed, and the qq?-nonet classification of the observed states is settled. The analysis shows an existence of the scalar glueball state in the mass region 1300–1600 MeV. The pure glueball state is dispersed over three real resonances: f ₀(1300), f ₀(1500), and f ₀(1530 ± ₂₅₀ ⁹⁰ ). Glueball/qq?content of these resonances is restored.     

Qualitative features of the glueball spectrum

The low-energy meson spectrum is investigated. Quantum numbers of the lightest glueballs are obtained by studying low-dimension, gauge invariant, colorless operators. A general shell model of hadrons is formulated and its predictions are specified. A comparison and criticism of existing glueball models is included.     

The glueball mass spectrum in QCD: First results of a lattice Monte Carlo calculation

We perform a variational calculation of the masses of glueballs of various spins and parities in SU(2) gauge theory. The quantum vacuum we use is generated by the lattice Monte Carlo technique. Our first results, obtained on medium sized lattices give m(0⁺) = (3.6 ± 0.35) Λ_mom, m(0^? = (6.0 ± 1.0)Λ_mom, m(2⁺) = (6.5^+1.8_?1.1)Λ_mom, various mass upper bounds and information on glueball wave functions.     

Search for the isovector member of the scalar nonet

The identification of the isovector member of the scalar nonet plays a fundamental role in fixing the properties of the other members and, therefore, in the possible identification of an extra state as the glueball candidate. After more than 20 years of experiments on this subject the situation has not yet been clarified. A review of the experimental results coming both from annihilation and the reaction is presented in this paper. Received: 3 September 1998 / Published online: 7 April 1999     

Gluon effects and nonet mixing in the current quark picture

The effects on the meson mass spectrum of gluon interactions, and in particular of quark annihilation diagrams, are investigated in the current quark framework. The resulting mixing scheme leads to mixing angles θp ? ?13° and θ_V ? ? 52° for the pseudoscalar and vector nonets respectively, in moderate agreement with present data on radiative decays. For virtual electromagnetic processes additional gluon diagrams play a role. In η → 3π the net effect is to almost double the current algebra prediction, while in ω → 2π the ω → ?⁰ transition amplitude is correctly predicted in both sign and magnitude. The relation between the Hamiltonian approach and the U(1) problem, as formulated in terms of axial divergences, is briefly discussed.     

Understanding the scalar mesonq\bar q nonet

It is shown that one can fit the available data on thea _o(980),f _o(1300) andK _o ^* (1430) mesons as a distorted 0⁺⁺ nonet using very few (5–6) parameters and an improved version of the unitarized quark model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. The parameters include a bare or mass, an over-all coupling constant, a cutoff and a strange quark mass of 100 MeV, which is in accord with expectations from the quark model. It is found that in particular for thea ₀(980) andf ₀(980) the component, in the wave function is large, i.e., for a large fraction of the time the state is transformed into a virtual pair. This component, together with a similar component of for thea ₀(980), and , and components for thef ₀(980), causes the substantial shift to a lower mass than what is naively expected from the component alone. Mass, width and mixing parameters, including sheet and pole positions, of the four resonances are given, with a detailed pedagogical discussion of their meaning.