Single pseudoscalar meson production in diffractive ep scattering

Exclusive pseudoscalar meson production in 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 , and production. Results are given from both a full calculation and one using the equivalent photon approximation. The accuracy of the latter is discussed. Received: 18 December 1997 / Published online: 10 March 1998     

Vector meson production by inelastic scattering of polarized electrons off polarized nucleons

A general analysis of vector meson production by inelastic scattering of polarized electrons (or muons) off polarized nucleons is presented. Cross section and vector meson decay angular distribution are discussed in terms of s-channel helicity amplitudes for natural and unnatural parity exchange. The question of experiments suitable for analyzing the more refined dynamical features of ?⁰-production is discussed in detail. Estimates are given for the effects to be expected from unnatural parity exchange.     

The diffraction cone for exclusive vector meson production in deep inelastic scattering

We develop the color dipole gBFKL phenomenology of a diffraction cone for photo-and electroproduction γ*N−VN of heavy vector mesons (charmonium & bottomonium) at HERA and in fixed target experiments. We predict a substantial shrinkage of the diffraction cone from the CERN/FNAL to the HERA range of c.m.s. energy W. The Q ²-controlled sensitivity to the color dipole size (scanning phenomenon) is shown to lead to a decrease of the diffraction slope with Q ² (which is supported by the available experimental data). We predict an approximate flavor independence of the diffraction slope in the scaling variable Q ²+m _V ² . For diffractive production of the radially excited 2S states (Ψ′, γ′), a counterintuitive inequality of diffraction slopes B(2S)≲B(1S) is predicted, which defies the common wisdom that diffraction slopes are larger for reactions with larger size particles. Zh. éksp. Teor. Fiz. 113, 1930–1962 (June 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Isospin symmetry violation, meson production and η-nucleus interaction studies

We have studied isospin symmetry violation in nuclear reactions by measuring simultaneously the cross-section of the following two reactionsp +d →³H π⁺ andp +d →³He π⁰. The experiment was perfomed at the cooler synchrotron accelerator COSY, Jülich at several beam energies close to the correspondingη production threshold. We also have ongoing programmes onη-nucleus final-state interaction studies viap+⁶ Li →⁷ Be +η reactions, high resolution search for dibaryonic resonances and lambda-proton final state interaction studies. The experimental details and results obtained so far are presented here     

Recent progress in the theory of hypernuclei

Importance of polarized hypernucleus production and its subsequent use for coincidence measurements is stressed. Cross-sections and polarizations in the (⁺, K⁺) reaction are formulated and calculated. As one of the new hypernuclear production reactions, relativistic nucleusnucleus collisions are theoretically studied and the results are compared with recent Dubna data.Invited talk to the symposium Mesons and Light Nuclei IV, Bechyn, Czechoslovakia, September 5–10, 1988.The author is greatly indebted to J. ofka, M. Sotona, T. Motoba, R. Mach, M. Sano and M. Wakai for continuous collaboration.     

Polarised electron-hadron scattering and weak interaction theory

It is shown that the naive valence quark parton model assumptions used to calculate the parity violation in polarisede-d scattering are not needed in order to extract informations from the experimental data about the neutral current couplings. Much more general assumptions which can be justified within the QCD approach are sufficient in order to arrive at essentially the same conclusions for the neutral current coupling parameters     

Binding energies of hypernuclei and ΛN interaction

A central ΛN potential V _ΛN is found on the basis of an analysis of the binding energies of 1s-shell hypernuclei and Λp scattering. Within the exprerimental errors, this potential makes it possible to reproduce the binding energies of three-, four-, and five-particle ground and excited states of hypernuclei and the angular and energy dependences of the cross sections for Λp scattering. The accuracy and reliability of the calculation of three-, four-, and five-particle hypernuclear and the respective nuclear systems is ensured by determining both upper and lower bounds on the energy. Within the Λ plus core model, the potential V _ΛN is matched with binding energies of heavy hypernuclei.     

Binding energies of hypernuclei and ΛN interaction

A central ΛN potential V _ΛN that describes, in the limits of experimental errors, the binding energies of three-, four-, and five-particle ground and excited states of hypernuclei, as well as energy and angular dependence of Λp scattering cross sections, is found on the basis of a conjoint analysis of binding energies of 1s-shell hypernuclei and Λp scattering. The reliability and accuracy of three-, four-, and five-particle calculations of hypernuclei and related nuclear systems are assured by the estimation of, an upper, as well as a lower bound of energy. In the framework of the model Λ+core, V _ΛN agrees with binding energies of heavy hypernuclei.     

DN interaction from meson exchange

A model of the DN interaction is presented which is developed in close analogy to the meson-exchange [`(K)] \bar{{K}} N potential of the Jülich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (r \rho , w \omega exchange and higher-order box diagrams involving D <sup>*</sup> N , D D \Delta , and D <sup>*</sup> D \Delta intermediate states. The coupling of DN to the p \pi L<sub>c</sub> \Lambda_{c}^{} and p \pi S<sub>c</sub> \Sigma_{c}^{} channels is taken into account. The interaction model generates the L<sub>c</sub> \Lambda_{c}^{}(2595) -resonance dynamically as a DN quasi-bound state. Results for DN total and differential cross sections are presented and compared with predictions of two interaction models that are based on the leading-order Weinberg-Tomozawa term. Some features of the L<sub>c</sub> \Lambda_{c}^{}(2595) -resonance are discussed and the role of the near-by p \pi S<sub>c</sub> \Sigma_{c}^{} threshold is emphasized. Selected predictions of the orginal [`(K)] \bar{{K}} N model are reported too. Specifically, it is pointed out that the model generates two poles in the partial wave corresponding to the L \Lambda(1405) -resonance.     

Axial vector meson production

Recently available differential cross section and density matrix information on π^?p → B^?p at 4 GeV/c are successfully described in terms of t channel exchanges and s channel absorptive effects. The s channel helicity amplitude which is dominant at small |t| (zero net helicity flip ω exchange) is found to have a zero at ?t = 0.2 GeV². SU(3) and higher symmetries are used to predict cross sections for further axial vector meson production processes, in particular non-diffractive A₁ production. The importance of these processes with regard to Regge phenomenology and meson spectroscopy is emphasized.     

Double hypernuclei and the Λ-Λ interaction

The binding energy of the double hypernucleus Be¹⁰ analyzed using an -particle model. A relationship is found between B, the binding energy of two -particlcs, and ¯V, the - potential integral. For the experimental value B = 17.5 Me V ¯V varies from 250 to 850 MeV-F³ according to the form of the - potential used.In conclusion, I wish to thank S. N. Kryuchkova for carrying out these calculations on a Minsk-2 electronic computer. I also wish to thank my senior colleague, V. A. Filimonov, for his support in the completion of the present work.     

Non-diffractive production of meson resonances

We study the peripheral cross sections of resonances that cannot be produced by π-exchange. In particular, we concentrate on the four meson nonets expected as L = 1 quark states (i.e., the J^P = 0⁺π_N(980); J^P = 1⁺ A₁, B; J^P = 2⁺ A₂). We use SU(3), Regge poles, factorization, exchange degeneracy, pole extrapolation, and the vector-meson-photon analogy. We predict the cross sections in both photoproduction and non-diffractive hadronic reactions. In passing, we discuss the large unnatural-parity (B, K?Q_B) exchange contributions and even the possibility of studying ππ → πω while avoiding the B production background.     

Two-photon mechanism of scalar meson production by colliding beams

Cross sections of scalar mesons f ₀(980), a ₀(980), and σ(600) production by colliding electron-positron beams are calculated. Two-photon decay widths of scalar mesons obtained in the Nambu-Jona-Lasinio model are used with quark and meson loops taken into account.     

Absorptive corrections to associated production of strange baryon and meson resonances in πp scattering

Absorptive corrections are calculated for the reactionsπ ⁺ p→K ^*+∑⁺(K ^*+ Y ₁ ^*+ ) mediated byK-exchange andπ ⁺p→K⁺ Y ₁ ^*+ withK ^*-exchange. The effect of the finite width of the resonances is included. Numerical results are given for 5 and 8 GeV/c.     

Asymptotic energy scale factors for pseudoscalar meson scattering and charmed meson couplings

Energy scale factors ν₀ for PP → PP scattering amplitudes are related via the absence of exotic resonances to ratios of tensor to vector coupling strengths. These same ratios are extracted from FESR's for non-exotic reactions. The scale factors obtained are all of the order of 1.0 GeV²or less, independent of quantum numbers. This contradicts the expectations of dual amplitudes in which ν₀ = 1/α′, and trajectory slopes are smaller for charmed mesons. Decay widths for tensor mesons are predicted. An observed SU(3) violation for the ratio $\text{A}{}_2\text{→}\text{K}\text{K}\text{/}\text{K}{}^7\text{→}\text{K}\text{π}$ is shown to be consistent with the FESR results. Charmed meson decays are predicted to be factors of 2–3 larger than those predicted by SU(4).     

Binding energies of λλ hypernuclei and the λλ interaction

The binding energies of the ΛΛ hypernuclei ¹⁰_ΛΛBe and ⁶_ΛΛHe are calculated variationally with a 2α + 2Λ and with an α + 2Λ model, respectively. For ¹⁰_ΛΛBe the integrations were made with Monte Carlo techniques while for ⁶_ΛΛHe direct numerical methods were used. A wide range of phenomenological ΛΛ potentials based on meson-exchange models was considered. An approximately universal linear relation between the calculated values of $\text{B}{}_{\mathrm{\Lambda \Lambda }}\text{(}{}^{10}{}_{\mathrm{\Lambda \Lambda }}\text{Be}\text{)}$ and of $\text{B}{}_{\mathrm{\Lambda \Lambda }}\text{(}{}^6{}_{\mathrm{\Lambda \Lambda }}\text{He}\text{)}$ is obtained. For the experimental value of $\text{B}{}_{\mathrm{\Lambda \Lambda }}\text{(}{}^{10}{}_{\mathrm{\Lambda \Lambda }}\text{Be}\text{) = 17.7 ± 0.1}\text{MeV}$ this relation predicts a much too small value of $\text{B}{}_{\mathrm{\Lambda \Lambda }}\text{(}{}^6{}_{\mathrm{\Lambda \Lambda }}\text{He}\text{)}$, well below the lower limit of the quoted experimental value of 10.9 ± 0.6 MeV. For ΛΛ potentials with repulsive cores the relations, for a given $\text{B}{}_{\mathrm{\Lambda \Lambda }}\text{(}{}^{10}{}_{\mathrm{\Lambda \Lambda }}\text{Be}\text{)}$, between the low-energy ΛΛ scattering parameters a, r₀ and the intrinsic range b are both approximately universal and independent of the detailed potential shape. For the experimental value of $\text{B}{}_{\mathrm{\Lambda \Lambda }}\text{(}{}^{10}{}_{\mathrm{\Lambda \Lambda }}\text{Be}\text{)}$ the preferred values are 2.5 ? ?a ? 3.5 fm, 2.6 ? r₀ ? 3.1 fm. The large and negative values of a correspond to conditions not too far from a bound ¹S₀ ΛΛ state and could indicate a 6-quark dibaryon state with the same quantum numbers and above the ΛΛ threshold.