184 research outputs found

    Near-threshold production of a0(980) mesons in the reaction pp -> d K^+ \bar{K}^0

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    Using an effective Lagrangian approach as well as the Quark-Gluon Strings Model we analyze near-threshold production of a0(980)-mesons in the reaction NN -> d K \bar{K} as well as the background of non-resonant K\bar{K}-pair production. We argue that the reaction pp -> d K^+ \bar{K}^0 at an energy release Q<=100 MeV is dominated by the intermediate production of the a0(980)-resonance. At larger energies the non-resonant K^+\bar{K}^0-pair production - where the kaons are produced in a relative P-wave - becomes important. Then effects of final-state interactions are evaluated in a unitarized scattering-length approach and found to be in the order of a 20% suppression close to threshold. Thus in present experiments at the Cooler Synchrotron COSY-J\"ulich for Q<=107 MeV the a_0^+ signal can reliably be separated from the non-resonant K^+\bar{K^0} background.Comment: 14 pages, 12 figures, submitted to EPJ

    Photon induced Lambda(1520) production and the role of the K^* exchange

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    We study the photon induced Lambda(1520) production in the effective Lagrangian method near threshold, E_\gamma^{LAB}<2 GeV, and in the quark-gluon string model at higher energies 3 GeV < E_\gamma^{LAB} < 5 GeV. In particular, we study the role of the K^* exchange for the production of Lambda(1520) within the SU(6) Weinberg-Tomozowa chiral unitary model proposed in Phys. Rev. D74 (2006) 034025. The coupling of the Lambda(1520) resonance to the N \bar K^* pair, which is dynamically generated, turns out to be relatively small and, thus, the K exchange mechanism dominates the reaction. In the higher energy region, where experimental data are available, the quark-gluon string mechanism with the K Regge trajectory reproduces both the energy and the angular distribution dependences of the Lambda(1520) photo-production reaction.Comment: 20 pages and 6 page

    Production of a0a_0-mesons in the reactions πNa0N\pi N \to a_0 N and ppda0+p p \to d a_0^+ at GeV energies

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    We investigate the reactions πNa0N\pi N \to a_0 N and ppda0+p p \to d a_0^+ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different contributions to the cross section of the reaction πNa0N\pi N \to a_0 N. These results are used to calculate the differential and total cross sections of the reaction ppda0+p p \to d a_0^+ within the framework of the two-step model in which two nucleons produce an a0a_0-meson via π\pi -meson exchange and fuse to a deuteron. The necessity of new measurements on a0a_0 production and branching fractions (of its decay to the KKˉK\bar K and πη\pi\eta channels) is emphasized for clarifying the a0a_0 structure. Detailed predictions for the reaction ppda0+pp \to d a_0^+ are presented for the energy regime of the proton synchrotron COSY-J\"ulich.Comment: 9 pages, including 6 eps figure

    Deuteron photodisintegration within the Quark-Gluon Strings Model and QCD motivated nonlinear Regge trajectories

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    We investigate deuteron two-body photodisintegration within the framework of the Quark-Gluon Strings Model with nonlinear baryon Regge trajectories. Special attention is paid to the use of QCD motivated Regge trajectories of the logarithmic and square-root form which have been suggested recently by Brisudov\'{a}, Burakovsky and Goldman. We find that the recent experimental data from TJNAF in the few GeV region can reasonably be described by the model. Angular distributions at different γ\gamma-energies are presented and the effect of a forward-backward asymmetry is discussed. Predictions for the energy dependence of dσ/dtd\sigma/dt at higher energies and different Θcm\Theta_{cm} are presented, too.Comment: 21 pages, LaTeX, including 6 postscript figures; submitted to Phys. Rev.

    Polarization observables in high-energy deuteron photodisintegration within the Quark-Gluon Strings Model

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    Deuteron two-body photodisintegration is analysed within the framework of the Quark-Gluon Strings Model. The model describes fairly well the recent experimental data from TJNAF in the few GeV region. Angular distributions at different γ\gamma-energies are presented and the effect of a forward-backward asymmetry is discussed. New results from the QGSM for polarization observables from 1.5 -- 6 GeV are presented and compared with the available data.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002, Juelich, June 10-14, 200

    Near-threshold production of a0(980)a_0(980)-mesons in πN\pi N and NN collisions and a0/f0a_0/f_0-mixing

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    We consider near-threshold a0(980)a_0(980)-meson production in πN\pi N and NNNN collisions. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also evaluated for comparison. The results from πN\pi N reactions are used to calculate the contribution of the a0a_0 meson to the cross sections and invariant KKˉK \bar K mass distributions of the reactions pppnK+Kˉ0pp\to pn K^+\bar K^0 and ppppK+Kpp\to pp K^+K^-. It is found that the experimental observation of a0+a_0^+ mesons in the reaction pppnK+Kˉ0pp\to pn K^+\bar K^0 is much more promising than the observation of a00a_0^0 mesons in the reaction ppppK+Kpp\to pp K^+K^-. Effects of isospin violation in the reactions pNda0pN \to d a_0, pd3He/3Ha0pd \to \mathrm{^3He/^3H} a_0, and dd4Hea0 dd \to \mathrm{^4He} a_0, which are induced by a0(980)a_0(980)--f0(980)f_0(980) mixing, are also analyzed.Comment: 43 pages, including 16 eps figures, to be bublished in Phys. Atom. Nucl. (Yad. Fiz.) vol. 65, No. 11 (2002

    Exclusive and semi-inclusive strangeness and charm production in πN\pi N and NNNN reactions

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    Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology we consider the reactions πpK0Λ\pi^- p \to K^0 \Lambda and πpDΛc+\pi^- p \to D^- \Lambda_c^+ which are dominated by the contributions of the KK^* and DD^* 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 πpK0Λ\pi^- p \to K^0 \Lambda 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 πpDΛc+\pi^- p \to D^- \Lambda_c^+. Employing the latter results from πp\pi^- p reactions we then estimate the contributions of the pion exchange mechanism to the cross sections of the reactions NNNKΛNN \to NK\Lambda and NNNDˉΛcNN \to N\bar D \Lambda_c and compare them with the contributions of the KK and DD exchanges. We find that the NNNN reactions are dominated not by pion exchange but by KK and DD exchanges, respectively. Moreover, assuming the SU(4) symmetry to hold approximately for the coupling constants gNDΛcg_{ND \Lambda_c} = gNKΛg_{NK \Lambda} we analyze also the production of leading Λc\Lambda_c hyperons in the reaction NNΛcXNN \to \Lambda_c X. It is shown that the non-perturbative mechanism should give an essential contribution to the Λc\Lambda_c yield for x0.5x \geq 0.5.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002, Juelich, June 10-14, 200
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