Results 1 - 10 of 306105
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[en] The role of hadron dynamics in the nucleus is illustrated to show the importance of nuclear medium effects in hadron interactions. The low lying hadron spectrum is considered to provide the natural collective variable for nuclear systems. Recent studies of nucleon-nucleon and delta-nucleon interactions are reviewed, with emphasis on the type of experimental phenomena which signal the importance of the many-body dynamics
[en] We present a study on hyperon/anti-hyperon production asymmetries in the framework of the recombination model. The production asymmetries for Λ 0/Λ-bar 0 Ξ -/Ξ + and Ω -/ Ω + are studied as a function of xF. Predictions of the model are compared to preliminary data on hyperon/anti-hyperon production asymmetries in 500 GeV/c π-p interactions from the Fermilab E791 experiment. The model predicts a growing asymmetry with the number of valence quarks shared by the target and the produced hyperons in the xF < 0 region. In the positive xF region, the model predicts constant asymmetries for Λ 0/Λ-bar 0 and Ω -/ Ω + production and a growing asymmetry with xF for Ξ -/Ξ + . We found a qualitatively good agreement between the model predictions and data, showing that recombination is a competitive mechanism in the hadronization process. (author)
[en] We calculate the helicity-changing amplitude of elastic nucleon--nucleon scattering, which is determined by the contribution of the nucleon and Δ33 isobar in the intermediate state. Spin effects in high-energy pp scattering are described with strong meson--nucleon form factors and pre-asymptotic contributions taken into account
[en] An important question about resonance extraction is how much resonance poles and residues extracted from data depend on a model used for the extraction, and on the precision of data. We address this question with the dynamical coupled-channel (DCC) model developed in Excited Baryon Analysis Center (EBAC) at JLab. We focus on the P11 pi-N scattering. We examine the model-dependence of the poles by varying parameters to a large extent within the EBAC-DCC model. We find that two poles associated with the Roper resonance are fairly stable against the variation. We also develop a model with a bare nucleon, thereby examining the stability of the Roper poles against different analytic structure of the P11 amplitude below pi-N threshold. We again find a good stability of the Roper poles.
[en] The work done during the past year or so may be divided into three separate areas, low energy nuclear reactions, intermediate energy physics and nuclear structure studies. In this paper, we shall separately summarize our achievements made in these three areas
[en] We study the stability of resonance poles in πN P11 partial wave, particularly the Roper resonance, by varying parameters significantly within the EBAC dynamical coupled-channels model, keeping a good fit to the empirical amplitude. We find that two Roper poles are stable against the variation. However, for higher energies, the number of poles can change depending on how the parameters are fitted within error bars. We also developed a model with a bare nucleon which forms the physical nucleon by being dressed by the meson-cloud. We still find a good stability of the Roper poles.
[en] We address a question about how much resonance poles and residues extracted from data depend on a model used for the extraction, and on the precision of data. We focus on the P11 π-N scattering and use the dynamical coupled-channel (DCC) model developed in Excited Baryon Analysis Center (EBAC) at JLab. We examine the model-dependence of the poles by varying parameters largely within the EBAC-DCC model. We find that two poles associated with the Roper resonance are fairly stable against the variation. We also study the stability of the Roper poles against different analytic structure of the P11 amplitude below π-N threshold by using a bare nucleon model. We again find a good stability of the Roper poles.
[en] We present an alternative interpretation for the dynamical origin of the P11 nucleon resonances, which results from the dynamical coupled-channels analysis at Excited Baryon Analysis Center of Jefferson Lab. The results indicate the crucial role of the multichannel reaction dynamics in determining the N* spectrum. An understanding of the spectrum and structure of the excited nucleon (N*) states is a fundamental challenge in the hadron physics. The N* states, however, couple strongly to the meson-baryon continuum states and appear only as resonance states in the γN and πN reactions. One can expect from such strong couplings that the (multichannel) reaction dynamics will affect significantly the N* states and cannot be neglected in extracting the N* parameters from the data and giving physical interpretations. It is thus well recognized nowadays that a comprehensive study of all relevant meson production reactions with πN,ηN,ππN,KY, (horellipsis) final states is necessary for a reliable extraction of the N* parameters. To address this challenging issue, the Excited Baryon Analysis Center (EBAC) of Jefferson Lab has been conducting the comprehensive analysis of the world data of γN,πN → πN,ηN,ππN,KY, (horellipsis) reactions systematically, covering the wide energy and kinematic regions. The analysis is pursued with a dynamical coupled-channels (DCC) model, the EBAC-DCC model, within which the unitarity among relevant meson-baryon channels, including the three-body ππN channel, is fully taken into account.