Investigation of a quasi-bound T = 2 (NΔ) state with increased lifetime of the Δ

The (NΔ) system has been investigated to see whether a quasi-bound state exists for which the lifetime of the Δ is considerably increased. The (NΔ) interaction using π- and ρ-meson exchange has been studied for various approximations. In particular, the Δ-nucleon mass difference and the Δ-width have been included leading to a complex (NΔ) potential. One finds that the (T = 2, J^P = 2⁺ state is bound with a binding energy of 10 to 40 MeV depending on the type of potential used and on the regularization range. Furthermore, for this state the decay width of the Δ is strongly reduced by binding effects and the Pauli principle. The reduction amounts to a factor of three to five.     

The exchange of ρ-mesons in π-d and π-4He elastic scattering

A rescattering process for π-deuteron and π?⁴He elastic scattering in which the intermediate state contains a ρ-meson instead of the π-meson is studied in the energy region of the 3,3 pionnucleon resonance. It is found that the contribution of such a process is negligible in the forward direction, but amounts to some 5 % to 10 % (or even more) of the cross sections at large angles. Great sensitivity to the off-shell behavior of the NΔ vertex and to the short-range two-body correlations in the nucleus is found.     

Two-pion exchange contributions to theK +-p potential

Employing perturbation theory aK ⁺-meson proton potential resulting from two-pion exchange is obtained. Recoil effects are taken into account. For short distances we add a phenomenological hard core interaction and calculates-wave phase shifts.     

Medium polarization and short-range effects in the meson exchange charge operator

The role of the medium polarization caused by the pion and rho-meson interactions in nuclear media for the corresponding meson exchange contributions to nuclear charge form factors is investigated. It is shown that the medium polarization and short-range effects slightly reduce the pion exchange contribution but that this reduction is more than compensated for by the ρ-meson exchange contribution. The combined pion and ρ-meson contributions to nuclear charge form factors is larger than previously estimated pion exchange corrections obtained without account of the medium polarization.     

Substitution effect of Ba at the Sr sites in Sr(Fe,Re)O3

We study ?-meson production in nuclei to investigate the in-medium modification of the ?-meson spectral function at finite density. We consider ( ${\bar p},\phi$ ), (γ,p) and (π ^???, n) reactions to produce a ?-meson inside the nucleus and evaluate the effects of the medium modifications to reaction cross sections. The structures of the bound states, ?-mesic nuclei, are also studied. For strong absorptive interaction cases, we need to know the spectrum shape in a wide energy region to deduce the properties of ?.     

Dibaryon Concept for Short-Range 2N and 3N Forces: Consequences for Hadronic and Nuclear Physics

The short-range aspects of 2N and 3N nuclear interactions are considered in light of numerous novel experimental data obtained in JLab, BNL, Mainz, etc. Many of these new experimental results contradict strongly to the traditional models for short-range (or high-momentum) components of nuclear forces and therefore require a novel understanding within new models alternative to the traditional (one-boson-exchange) ones. At the NN distances r _{N N} < 1 fm the nucleon quark cores get overlapped with each other and thus the generation of the common six-quark bag is very likely. So, the dibaryon concept considers the generation of the intermediate six-quark bag dressed with meson (predominantly the scalar-isoscalar σ-meson) clouds as a driving mechanism for short-range nuclear force. Numerous predictions of the above dibaryon model are considered in the paper.     

Interionic potentials for alkali halide crystals derived by the hybrid Thomas-Fermi-Dirac method

The first results of a systematic study of interatomic potentials in sixteen alkali halides derived using the hybrid Thomas-Fermi-Dirac method are presented. Both the basic method and modifications to (a) correct the exchange energy to exclude the self-exchange part and (b) scale the kinetic and exchange energy terms are employed. The interactions between ion pairs are calculated at a set of interionic distances in a range corresponding to ± 30% deviations from the appropriate measured equilibrium separation. In this way a tabular function for the lattice energy/ion pair is constructed and predicted values of the equilibrium nearest neighbour interionic distance, the equilibrium lattice energy/ion pair and the Smith stiffness parameter are found numerically. The derived short-range interactions between ion pairs are fitted over the whole range to the analytic form A exp($\text{?R}\text{ρ}$) + CR^?6. It is shown that the use of an expression for the lattice energy/ion pair involving these analytic forms introduces significant errors in the predicted physical parameters.     

Absorptive corrections in the photoproduction of charged π-mesons

A Regge-pole model with π-, ?-,A ₂- andR-meson exchange and absorptive corrections are used to reproduce the π^± photoproduction data in the larges, small ¦t¦ region. The starting point for the calculation of the absorptive corrections is the Regge-pole model for invariant functions.     

On new predictions of the vector-meson dominance model for the reactions πN → ϱ0N and γN → πN

It is shown that the assumption of pole vector-meson dominance for the Ball invariant amplitude having a π-meson pole is sufficient for reproducing the longitudinal amplitude of ?⁰-production by the photoproduction amplitude at |t| < 0.1 (GeV/c)². The strong k²-dependence of the Ball invariant amplitude without the π-meson pole has been found by the deviations of theoretical predictions obtained in the VDM framework for the longitudinal ?⁰-production amplitude from the experimental data in the region |t| > 0.1 (GeV/c)². A natural explanation of the k²-dependence in the one-pion exchange model with absorption is given. The problem of A₂-exchange is discussed.     

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.     

Anomalous quark-gluon chromomagnetic interaction and high-energy ρ-meson electroproduction

It is shown that existence of a large anomalous chromomagnetic moment of quark induced by nonperturbative structure of QCD leads to the additional contribution to exclusive ρ-meson electroproduction off proton target. The contribution coming from new type of quark-gluon interaction to the ρ-meson production cross section for both transversal and longitudinal polarization of virtual photon is found. Such nonperturbative contribution together with conventional perturbative two-gluon exchange allows us to describe the experimental data at low Q ² for transversal polarization. However, in the longitudinal polarization case there is still some discrepancy with the data. The possible source of this deviation is discussed.     

Relativistic shell models and meson-exchange currents

We discuss the connection between nonrelativistic pair exchange currents and relativistic mean field theories. Heavy mesons, especially the σ-meson, are shown to yield strong enhancements to the matrix element of “odd” Dirac operators, such as γ and γ₄γ₅, in complete analogy to the strong enhancements obtained in relativistic mean field theories. For isoscalar operators, there is a cancelling contribution from ω-pair diagrams, called “backflow” in relativistic theories, but for isovector operators the equivalent ρ-pair diagram is very weak. Agreement between traditional nonrelativistic calculations and experiment is worsened by the introduction of heavy-meson pair diagrams. The situation can be improved on adding vertex form factors and short-range correlation functions that reduce the heavy-meson pair contribution by about a factor of two. The differences between the two approaches are emphasized and experimental tests are discussed.     

Rhoprimes in 6π states from materialisation of photons

Data on 6π states produced ine ⁺ e ^? annihilation and diffractive photoproduction are analysed together. The simplest interpretation is in terms of two major contributions from resonances. One, in the isotopic spin symmetry state (321), peaks at 2.1 GeV and the other, in the isotopic spin symmetry state (411), peaks at 1.8 GeV. The former is a candidate for a new ρ^′-meson. The latter could be an additional ρ^′-meson, but the possibility that it is a manifestation of the known ρ ₂ ^′ -meson, distorted by threshold effects, cannot be ruled out.     

Dipole interactions and diffusion of μ meson in copper

The dipole relaxation rate and the diffusion coefficient of μ⁺-meson in copper are measured at different temperatures. The activation energy of μ⁺-meson in a crystal of copper is determined.     

A global study of resonance production and of exchange processes inK − p interactions at 6.5 GeV/c

A sample of 3414 events of the typeK ^? p →K ^? pπ ⁺ π^? were recorded in the ANL 12-foot hydrogen bubble chamber exposed to aK ^?-meson beam of 6.5 GeV/c momentum. The total cross section for this reaction (1.17±0.07 mb), is compared to data obtained at neighbouring energies. Resonance production is studied using two complementary procedures; an analytical multichannel fit and multidimensional cluster methods. Baryon exchange processes, accounting for approximately 5% of the data, are isolated by the latter method.     

About ω0-exchange in the (γ, π0) reaction on the proton near threshold

With the amplitudes obtained in the effective lagrangian (BL) and in the dispersion (BDW) methods the new data for the (γ, π⁰) reaction on the proton near threshold are analysed. The inclusion of ω⁰-meson exchange in the BDW amplitude removes the discrepancy with experimental data. The tensor and vector coupling constants which are consistent with the results of other analyses give the value of E₀₊ multipole predicted by the PCAC hypothesis.     

Experimental and theoretical indications for an intermediate σ-dressed dibaryon in the NN interaction

Numerous theoretical and experimental arguments in favor of the generation of intermediate σ-dressed dibaryon in NN interaction at middle and short distances are presented. We argue that this intermediate dibaryon should be responsible for the strong middle-range attraction and the short-range repulsion in the NN interaction, and also for the short-range correlations in nuclei. The suggested mechanism for the σ-dressing of the dibaryon is identical to that which explains the Roper-resonance structure, its dominant decay mode and its extraordinary low mass. It is arguing that the (partial) chiral symmetry restoration effects, common for the Roper resonance and dressed dibaryon, are responsible for strong renormalizing of their masses and widths and the observed σ-meson mass and decay width as well. The new experimental data on 2π-production in the scalar-isoscalar channel produced in pn- and pd-collisions and recent data on γγ correlations in pC and dC scattering in the GeV region seems to corroborate the existence of the σ-dressed dibaryon in two- and three-nucleon interactions. A similar transformation mechanism from the glue to the scalar field can be valid also in some J/Ψ decays and in enormous σ-meson production in central pp collisions at high energies.     

Binding energy of the dihyperon in the quark cluster model

The dihyperon is described in the non-relativistic quark cluster model. The SU(3) flavor symmetry breaking due to the different quark masses is taken into account not only in the hamiltonian, but also in the quark wave functions. The interaction contains the one-gluon-exchange potential, pseudoscalar-meson exchange between quarks plus an additional phenomenological σ-meson exchange. The mass of the dihyperon is predicted to be (2211 ± 5) MeV, i.e. a binding energy of the dihyperon of (−20 ± 5) MeV below the ΛΛ threshold is found.     

Resonance production in the γγ→ππ process and low energy parameters

The amplitudes of the γγ→ππ reaction are obtained describing the process up to the energy of 1.5 GeV. It is shown that in thef-meson region there exists large background with the isospinI=2. This background and the backgrounds of the known mechanisms deal with the threshold expansion of the amplitude. This allows one to give polarizability estimate of the pion (α +β) ^π+ =0.45·10^?+fm, (α+β) ^π0. We predict a very small cross-section for the production of a broad ε (700) by using the low energy normalization.