A. Matsuyama

Osaka University, Ōsaka-shi, Osaka-fu, Japan

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Publications (40)112.5 Total impact

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    ABSTRACT: Within a multi-channels multi-resonances reaction model of pion nucleon reactions, we examine the properties of the nucleon resonances with masses less than 2GeV. The Roper resonance and the second resonance in P 11 are found to evolve dynamically from the same bare state. With the exception of the P 13 and P 31 resonances, our resonance pole positions agree well with the 3 and 4 star resonances listed by the Particle Data Group.
    Few-Body Systems 12/2010; 50(1):187-190. · 1.05 Impact Factor
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    ABSTRACT: We show that two almost degenerate poles near the piDelta threshold and the next higher mass pole in the P11 partial wave of piN scattering evolve from a single bare state through its coupling with piN, etaN, and pipiN reaction channels. This finding provides new information on understanding the dynamical origins of the Roper N{*}(1440) and N{*}(1710) resonances listed by Particle Data Group. Our results for the resonance poles in other piN partial waves are also presented.
    Physical Review Letters 01/2010; 104(4):042302. · 7.94 Impact Factor
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    ABSTRACT: The nucleon resonances appear as poles of the scattering amplitudes on the complex energy plane. The masses of N^* and the electromagnetic NN^* transition form factors are obtained from the pole positions and the residues of the scattering amplitudes. We have developed a method of analytic continuation to extract resonance parameters from the amplitudes of the dynamical reaction model, which includes unstable particle channels such as pi,N and rhoN. We apply the method for the piN and &*circ;N amplitudes from our coupled channel model of meson production reactions. The extracted NN^* form factors for a few N^* resonances will be presented.
    10/2009;
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    ABSTRACT: A comprehensive study of the meson production reactions with initial piN, gammaN, and N(e,e') based on a dynamical coupled-channels approach is being made to explore the structure of the N^* states in the Excited Baryon Analysis Center (EBAC) at Jefferson Lab. In this talk we present a current status of our study of the photo- and electro-production reactions, particularly focusing on the single and double pion production reactions. We will also discuss what impact the so-called ``complete-measurement'' of single pseudoscalar meson photoproduction reactions has on the construction of reaction models, which is a key to the precise determination of the N* properties.
    10/2009;
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    ABSTRACT: Within a dynamical coupled-channels model which has already been fixed from analyzing the data of the pi N -> pi N and gamma N -> pi N reactions, we present the predicted double pion photoproduction cross sections up to the second resonance region, W< 1.7 GeV. The roles played by the different mechanisms within our model in determining both the single and double pion photoproduction reactions are analyzed, focusing on the effects due to the direct gamma N -> pi pi N mechanism, the interplay between the resonant and non-resonant amplitudes, and the coupled-channels effects. The model parameters which can be determined most effectively in the combined studies of both the single and double pion photoproduction data are identified for future studies. Comment: Version to appear in PRC. 16 pages, 13 figures
    Physical Review C 09/2009; · 3.72 Impact Factor
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    ABSTRACT: Within the relativistic quantum field theory, we analyze the differences between the $\pi N$ reaction models constructed from using (1) three-dimensional reductions of Bethe-Salpeter Equation, (2) method of unitary transformation, and (3) time-ordered perturbation theory. Their relations with the approach based on the dispersion relations of S-matrix theory are dicusssed.
    Chinese Journal of Physics- Taipei- 02/2009; · 0.48 Impact Factor
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    ABSTRACT: We have performed a dynamical coupled-channels analysis of available p(e,e'pi)N data in the region of W
    Physical Review C 01/2009; 80(2). · 3.72 Impact Factor
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    ABSTRACT: Recent high precision data of the electromagnetic meson production reactions off nucleons from Bonn, GRAAL, JLab, Mainz and Spring-8 make possible to extract Q^2 dependence of the electromagnetic N-N^* transition form factors. To extract such information on the quark-gluon structures of the N^* states, a comprehensive analysis of the hadronic and electromagnetic meson production reactions is ongoing in Excited Baryon Analysis Center (EBAC) at JLab. The analysis is based on the dynamical coupled-channel model which properly describes correlations among all relevant reaction channels required from unitarity and can treat non-resonant and resonant processes in a unified manner. In this talk, we will report current status on the analysis of gammaN ->piN, gammaN ->etaN and e N ->e' piN reactions. The main purpose is to determine parameters associated with the electromagnetic interactions by this combined analysis of the electromagnetic meson production reactions. We will also discuss the N-N^* electromagnetic form factors extracted from the analysis of the e N ->e' piN reaction.
    10/2008;
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    ABSTRACT: As a step toward performing a complete coupled-channels analysis of the world data of pi N, gamma^* N --> pi N, eta N, pi pi N reactions, the pi N --> pi pi N reactions are investigated starting with the dynamical coupled-channels model developed in Phys. Rev. C76, 065201 (2007). The channels included are pi N, eta N, and pi pi N which has pi Delta, rho N, and sigma N resonant components. The non-resonant amplitudes are generated from solving a set of coupled-channels equations with the meson-baryon potentials defined by effective Lagrangians. The resonant amplitudes are generated from 16 bare excited nucleon (N^*) states which are dressed by the non-resonant interactions as constrained by the unitarity condition. The data of total cross sections and pi N and pi pi invariant mass distributions of pi^+ p --> pi^+ pi^+ n, pi^+ pi^0p and pi^- p --> pi^+ pi^- n, pi^- pi^0 n, pi^0 pi^0 n reactions from threshold to the invariant mass W = 2 GeV can be described to a very large extent. We show the importance of the coupled-channels effects and the strong interference between the contributions from the pi Delta, sigma N, and rho N channels. The large interference between the resonant and non-resonant amplitudes is also demonstrated. Possible future developements are discussed.
    Physical Review C 08/2008; · 3.72 Impact Factor
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    ABSTRACT: The electromagnetic pion production reactions are investigated within the dynamical coupled-channels model developed in {\bf Physics Reports, 439, 193 (2007)}. The meson-baryon channels included in this study are $\gamma N$, $\pi N$, $\eta N$, and the $\pi\Delta$, $\rho N$ and $\sigma N$ resonant components of the $\pi\pi N$ channel. With the hadronic parameters of the model determined in a recent study of $\pi N$ scattering, we show that the pion photoproduction data up to the second resonance region can be described to a very large extent by only adjusting the bare $\gamma N \to N^*$ helicity amplitudes, while the non-resonant electromagnetic couplings are taken from previous works. It is found that the coupled-channels effects can contribute about 10 - 20 % of the production cross sections in the $\Delta$ (1232) resonance region, and can drastically change the magnitude and shape of the cross sections in the second resonance region. The importance of the off-shell effects in a dynamical approach is also demonstrated. The meson cloud effects as well as the coupled-channels contributions to the $\gamma N \to N^*$ form factors are found to be mainly in the low $Q^2$ region. For the magnetic M1 $\gamma N \to \Delta$ (1232) form factor, the results are close to that of the Sato-Lee Model. Necessary improvements to the model and future developments are discussed.
    Physical Review C 01/2008; · 3.72 Impact Factor
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    ABSTRACT: As a first step to analyze the electromagnetic meson production reactions in the nucleon resonance region, the parameters of the hadronic interactions of a dynamical coupled-channels model, developed in Physics Reports 439, 193 (2007), are determined by fitting the πN-scattering data. The channels included in the calculations are πN,ηN, and ππN, which has πΔ,ρN, and σN resonant components. The nonresonant meson-baryon interactions of the model are derived from a set of Lagrangians by using a unitary transformation method. One or two bare excited nucleon states in each of S,P,D, and F partial waves are included to generate the resonant amplitudes in the fits. The parameters of the model are first determined by fitting as much as possible the empirical πN elastic-scattering amplitudes of SAID up to 2 GeV. We then refine and confirm the resulting parameters by directly comparing the predicted differential cross section and target polarization asymmetry with the original data of the elastic π±p→π±p and charge-exchange π-p→π0n processes. The predicted total cross sections of πN reactions and πN→ηN reactions are also in good agreement with the data. Applications of the constructed model in analyzing the electromagnetic meson production data as well as the future developments are discussed.
    Physical Review C 12/2007; 76(6). · 3.72 Impact Factor
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    ABSTRACT: As a first step to analyze the electromagnetic meson production reactions in the nucleon resonance region, the parameters of the hadronic interactions of a dynamical coupled-channel model, developed in {\it Physics Reports 439, 193 (2007)}, are determined by fitting the $\pi N$ scattering data. The channels included in the calculations are $\pi N$, $\eta N$ and $\pi\pi N$ which has $\pi\Delta$, $\rho N$, and $\sigma N$ resonant components. The non-resonant meson-baryon interactions of the model are derived from a set of Lagrangians by using a unitary transformation method. One or two bare excited nucleon states in each of $S$, $P$, $D$, and $F$ partial waves are included to generate the resonant amplitudes in the fits. The parameters of the model are first determined by fitting as much as possible the empirical $\pi N$ elastic scattering amplitudes of SAID up to 2 GeV. We then refine and confirm the resulting parameters by directly comparing the predicted differential cross section and target polarization asymmetry with the original data of the elastic $\pi^{\pm} p \to \pi^{\pm} p$ and charge-exchange $\pi^- p \to \pi^0 n$ processes. The predicted total cross sections of $\pi N$ reactions and $\pi N\to \eta N$ reactions are also in good agreement with the data. Applications of the constructed model in analyzing the electromagnetic meson production data as well as the future developments are discussed.
    05/2007;
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    A. Matsuyama, T Sato, T. -S. H. Lee
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    ABSTRACT: A dynamical coupled-channel model is presented for investigating the nucleon resonances in the meson production reactions induced by pions and photons. The model is based on an energy-independent Hamiltonian which is derived from a set of Lagrangians by using a unitary transformation method. By applying the projection operator techniques,we derive a set of coupled-channel equations which satisfy the unitarity conditions within the channel space spanned by the considered two-particle meson-baryon states and the three-particle $\pi\pi N$ state. We present and explain in detail a numerical method based on a spline-function expansion for solving the resulting coupled-channel equations which contain logarithmically divergent one-particle-exchange driving terms resulted from the $\pi\pi N$ unitarity cut. We show that this driving term can generate rapidly varying structure in the reaction amplitudes associated with the unstable particle channels. It also has large effects in determining the two-pion production cross sections. Our results indicate that cautions must be taken to interpret the $N^*$ parameters extracted from using models which do not include $\pi\pi N$ cut effects.
    Physics Reports 09/2006; · 22.93 Impact Factor
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    T. -S. H. Lee, A. Matsuyama, T Sato
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    ABSTRACT: It is shown that most of the models for analyzing meson-baryon reactions in the nucleon resonance region can be derived from a Hamiltonian formulation of the problem. An extension of the coupled-channel approach to include $\pi\pi N$ channel is briefly described and some preliminary results for the $N^*(1535)$ excitation are presented.
    07/2004;
  • Akihiko Matsuyama
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    Physics Letters B 01/1997; · 4.57 Impact Factor
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    Akihiko Matsuyama
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    Physics Letters A 01/1997; · 1.77 Impact Factor
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    Akihiko Matsuyama
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    Physics Letters A 06/1993; · 1.77 Impact Factor
  • A. Matsuyama, T.-S.H. Lee
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    ABSTRACT: The π+d ↔ pp reaction is studied within a unitary meson-exchange πNN model which was developed in our previous studies of NN and πd scattering. The predicted total cross sections are about of the data in the Δ resonance region. The calculated amplitudes in Jπ = 2+, 3− channels reproduce the resonant counter-clockwise behavior of Bugg's amplitude analysis. The predicted pp → πd angular distributions and analyzing powers are, however, only in qualitative agreement with the data. The dynamical content of our calculations is analyzed and compared with some of the previous approaches.
    Nuclear Physics A 01/1991; · 1.53 Impact Factor
  • A. Matsuyama, K. Yazaki
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    ABSTRACT: We have studied the behaviour of S-matrix poles near the thresholds for some three-body systems. In Amado's simple model for three bosons with an attractive S-wave two-body interaction and specetor angular momentum l=0, the S-matrix pole behaves as Im E ∞ -(ReE)2 near the threshold in the fourth quadrant of the unphysical complex E-plane. This behaviour is formally the same as that in the two-body scattering with angular momentum l=3/2 and a three-body resonance shows up near the threshold. In such a case, the Fredholm determinant of the Faddeev equation at zero energy, DF(0), is close to zero. However, it is shown that the value DF(0) does not definitely tell us whether the system is attractive or repulsive in contrast to the case of a two-body system. As physical applications, we have studied Lambdann and Sigma-nn systems. The S-matrix poles are found to be far away from the physical real axis and do not give rise to observable effects for the two-body interactions reproducing the low-energy scattering data, although the Lambdann system could develop a three-body resonance if the Lambdan interaction were slightly more attractive.
    Nuclear Physics A 01/1991; 534:620-636. · 1.53 Impact Factor
  • A. Matsuyama, K. Yazaki
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    ABSTRACT: The probabilities of hypernucleus formation by K- capture at rest are calculated in the bound state approximation for a wide range of target nuclei, i.e. 4He, 12C, 16O, 40Ca, 90Zr and 208Pb. The mass number dependence of the formation probabilities, the relative populations of the various states in the same nucleus and the effects of kaon- and pion-optical potentials are studied in detail. K- capture at rest seems less selective in populating hypernucleus states than other reactions such as (K, pi-/+) in flight and (pi+/-, K+).
    Nuclear Physics A 01/1988; 477(4):673-695. · 1.53 Impact Factor

Publication Stats

610 Citations
112.50 Total Impact Points

Institutions

  • 2010
    • Osaka University
      • Department of Physics
      Ōsaka-shi, Osaka-fu, Japan
    • Argonne National Laboratory
      • Division of Physics
      Lemont, Illinois, United States
  • 1987–2010
    • Shizuoka University
      • Department of Physics
      Sizuoka, Shizuoka, Japan
  • 2006–2009
    • Thomas Jefferson National Accelerator Facility
      Newport News, Virginia, United States
  • 1981–1991
    • The University of Tokyo
      • Department of Physics
      Tokyo, Tokyo-to, Japan
  • 1986
    • TRIUMF
      Vancouver, British Columbia, Canada
  • 1985–1986
    • Swiss Institute for Art Research
      Zürich, Zurich, Switzerland