Search

Using the Quark-Gluon Strings Model --combined with Regge phenomenology-- we perform a comparative analysis of Λ, Σ0, Λ(1520) and Θ+ production in binary reactions induced by photon, pion and proton beams on the nucleon. We find that the existing experimental data on the γ p↦ K+Λ differential and total cross-sections can be described very well by the model for photon energies 1-16 GeV and - t < 2 GeV2 assuming a dominant contribution of the K* Regge trajectory. Moreover, using the same parameters we also reproduce the total γ p↦ K+Σ0 and γ p↦ K+Λ(1520) cross-sections suggesting a “universality” of the Regge model. In order to check the consistency of the approach we evaluate the differential and total cross-sections for the reaction π- p↦ K0Λ which is also found to be dominated by the K* Regge trajectory. Using the apparent “universality” of the Regge model we extend our scheme to the analysis of the binary reactions γ p↦¯0Θ+, π- p↦ K-Θ+ and pp↦Σ+Θ+ as well as the exclusive and inclusive Θ+ production in the reactions pp↦ p¯0Θ+ and pp↦Θ+ X. Our detailed studies demonstrate that Θ+ production does not follow the “universality” principle, thus suggesting an essentially different internal structure of the exotic baryon relative to conventional hyperons or hyperon resonances. [ABSTRACT FROM AUTHOR]

The production of K+-mesons in proton-nucleus collisions from 1.0 to 2.3 GeV is analyzed with respect to one-step nucleon-nucleon (NN?NYK+) and two-step ?-nucleon (?N?K+ YN) or pion-nucleon (pN?K+ Y) production channels on the basis of a coupled-channel (CBUU) transport approach including the kaon final-state-interactions (FSI). Momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are included as well as K+ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental K+ spectra taken at COSY-Jülich. Our systematic analysis of K+ spectra from12C,63Cu,107Ag and197Au targets as well as their momentum differential ratios gives a repulsive K+ potential of 20±5 MeV at normal nuclear matter density. [ABSTRACT FROM AUTHOR]

Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. It is found that the forward-backward angle asymmetry predicted by the model is confirmed by the recent data at different photon energies from JLab. New calculations for polarization observables, the cross-section asymmetry Σ and the polarization transfer Cz', for photon energies (1.2-6) GeV are presented and compared with the data available up to 2 GeV. [ABSTRACT FROM AUTHOR]

The production and decay of vector mesons (p, w) in pA and AA reactions is studied with particular emphasis on their in-medium spectral functions. It is explored within transport calculations if hadronic in-medium decays like Π+π- or π°γ might provide complementary information to their dilepton (e+e-) decays. Whereas the π+&pi,- signal from the p-meson is found to be strongly distorted by pion rescattering, the w-meson Dalitz decay to π°γ appears promising even for more heavy nuclei in 7A and pA reactions. Furthermore, the influence of nucleon and kaon/antikaon potentials on the K± yields and spectra in pA collisions is calculated and compared to the recent data from the ANKE Collaboration. [ABSTRACT FROM AUTHOR]

: We study the perspectives of resonant charmonium production in p + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(2S) and Ψ(3770) on various nuclei, their propagation and decay to dileptons and D + D in the medium and vacuum, respectively, employing parametrizations for the D,D self-energies taken from QCD sum rule studies. The elastic and inelastic interactions of the charmonia and open-charm mesons in the medium are taken into account, too. It is found that the D,D invariant-mass spectra from light and heavy nuclei are not sufficiently sensitive to the in-medium properties of the Ψ(2S) and Ψ(3770). However, a “suppression” of low-mass dileptons from the Ψ(3770) might be seen experimentally as well as a small broadening of the Ψ(2S) dilepton spectra. [ABSTRACT FROM AUTHOR]

The lifetime of the Λ-hyperon in heavy hypernuclei measured in proton-Au, -Bi and -U collisions by the COSY-13 Collaboration at COSY-Jülich has been analyzed to yield τΛ = (145±11) ps. This value for τΛ is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, albeit much more accurate. Theoretical models based on the meson exchange picture and assuming the validity of the phenomenological Δ I = 1/2 rule predict the lifetime of heavy hypernuclei to be significantly larger (2-3 standard deviations). Such large differences indicate that at least one of the assumptions in these models is not fulfilled. A much better reproduction of the lifetimes of heavy hypernuclei is achieved in the phase space model, if the Δ I = 1/2 rule is discarded in the nonmesonic Λ decay. [ABSTRACT FROM AUTHOR]

The predictions for the production of nuclides and particles in proton-induced reactions are important e.g. for the detailed design of spallation neutron sources or accelerator-driven-systems. Computational tools are required that are able to describe quantitatively the two-stage process i.e. intra-nuclear cascade followed by evaporation-fission. The first stage is a highly non-equilibrated process in which incoming proton deposits in hot residual nucleus both excitation energy and angular momentum. The CBUU transport model calculation for few targets, for the proton energy range 0.4-2.0 GeV are presented, with the idea to find global parametrizations for the distributions of charge, mass, excitation energy, angular momentum of hot residual nuclei. [ABSTRACT FROM AUTHOR]

Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology we consider the reactions π-→ K0Λ and π-p→ D Λ+c which are dominated by the contributions of the K* and D* Regge trajectories, respectively. The spin structure of the amplitudes is described by introducing Reggeized Born terms. It is found that the existing data for the reaction π-p →K 0;Λ are in reasonable agreement with the model predictions. To describe the absolute values of the cross-sections it is necessary to introduce also suppression factors which can be related to absorption corrections. Furthermore, assuming the SU(4) symmetry to hold for Regge residues and the universality of absorption corrections we calculate the cross-section of the reaction π-p→D-Λ+C. Employing the latter results from π-p reactions we then estimate the contributions of the pion exchange mechanism to the cross-sections of the reactions NN → NKA and NN → NDACand compare them with the contributions of the K and D exchanges. We find that the NN reactions are dominated not by pion exchange but by K and D exchanges, respectively. Moreover, assuming the SU(4) symmetry to hold approximately for the coupling constants gND&lambdac= gNKA we analyze also the production of leading Λc-hyperons in the reaction NN ↠ΛcX. It is shown that the non-perturbative mechanism should give an essential contribution to theΛc yield for x &Ge;0.5. [ABSTRACT FROM AUTHOR]

: We study the perspectives of resonant charmonium production in p + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(2S) and Ψ(3770) on various nuclei, their propagation and decay to dileptons and D + D in the medium and vacuum, respectively, employing parametrizations for the D,D self-energies taken from QCD sum rule studies. The elastic and inelastic interactions of the charmonia and open-charm mesons in the medium are taken into account, too. It is found that the D,D invariant-mass spectra from light and heavy nuclei are not sufficiently sensitive to the in-medium properties of the Ψ(2S) and Ψ(3770). However, a “suppression” of low-mass dileptons from the Ψ(3770) might be seen experimentally as well as a small broadening of the Ψ(2S) dilepton spectra. [ABSTRACT FROM AUTHOR]