Masaki Arima

Dynamical test of constituent quark models with {pi}N reactions

A dynamical approach is developed to predict the {pi}N scattering amplitudes starting with the constituent quark models. The first step is to apply a variational method to solve the three-quark bound state problem. The resulting wave functions are used to calculate the N{sup *}{yields}{pi}N,{eta}N,{pi}{delta} vertex functions by assuming that the {pi} and {eta} mesons couple directly to quarks. These vertex functions and the predicted baryon bare masses then define a Hamiltonian for {pi}N reactions. We apply a unitary transformation method to derive from the constructed Hamiltonian a multichannel and multiresonance reaction model for predicting the {pi}N scattering amplitudes up to W=2 GeV. With the parameters constrained by the {delta}(1232) excitation, we have examined the extent to which the {pi}N scattering in the S{sub 11} channel can be described by constituent quark models based on one-gluon-exchange or one-meson exchange mechanisms. It is found that the data seem to favor the spin-spin interaction due to one-meson exchange and the tensor interaction due to one-gluon exchange. A phenomenological quark-quark potential has been constructed to reproduce the S{sub 11} amplitude. (c) 2000 The American Physical Society.

Kaonic Nuclei and Kaon-Nucleus Interactions

Although kaonic atoms provide valuable information concerning the K � -nucleus interaction at low energies, they cannot fully determine the K � -nucleus optical potential. We

Nucleon Resonances in a Constituent Quark Model with Chiral Symmetry.

The mass spectra of nucleon resonances with spin 1/2, 3/2, and 5/2 are systematically studied in a constituent quark model with meson-quark coupling, which is inspired by the spontaneous breaking of chiral symmetry of QeD. Meson-quark coupling gives rise not only to the one-meson-exchange potential between quarks but also to the self-energy of baryon resonances, owing to the existence of meson-baryon decay channels. These two contributions are consistently taken into account in the present model. The gross properties of nucleon resonance spectra are reproduced fairly well, although the predicted mass of N(1440) is too large.

Coherent pair state of the pion in the constituent quark model

A coherent state of pions is introduced to the nonrelativistic quark model. The coherent pair approximation is employed for the pion field in order to maintain the spin-isospin symmetry. In this approximation the pion is localized in the momentum space, and the vertex form factor in the pion-quark interaction is derived from this localization. The nucleon masses and wave functions are calculated using this model, and our results are compared to those of the quark model with the one pion exchange potential. Similar result is obtained for the mass spectrum, but there exists a clear difference in the internal structure of nucleon resonances.

Baryon Resonances in a Constituent Quark Model

The role of pseudoscalar mesons in the dynamical properties of baryon resonances is examinedby means of the constituent quark mod el with meson-quark coupling. Since resonance properties are closely relatedto meson-baryon scatterings, it is important to includ e reaction processes as well as mass spectra in the analysis. The isobar model is employed to properly extract information of baryon resonances from reaction amplitudes. Prominent features of resonance spectra are reproduced fairly well by taking account of baryon selfenergies due to meson-quark coupling. Several problems remained in the static quark model of baryons, e.g. Λ(1405)-Λ(1520) mass difference, are also studied. Brief comments on some improvements of the present model are given.

Effects of baryon resonances on nucleon–nucleon interactions in a quark model

Abstract Nucleon–nucleon S -wave scattering is studied by using the resonating group method, which includes not only the nucleon and Δ but also their excited states. As quark–quark interactions, the one-gluon-exchange and one-pion-exchange potentials are employed with phenomenological confinement potential. Compared with the N and Δ , coupling effects induced by excited-state baryons are small.

Analysis of (p,2p) reactions with production of pions in deep bound states

The production of the deeply bound pionic atom through (p,2p) reaction is studied theoretically. The cross sections for 208Pb are calculated by the distorted wave impulse approximation at 400 MeV.

Chiral symmetry and N*(1440){yields}N{pi}{pi} decay

The N*(1440){yields}N{pi}{pi} decay is studied by making use of the chiral reduction formula. This formula suggests a scalar-isoscalar pion-baryon contact interaction that is absent in the recent study of Hernandez et al. [Phys. Rev. C 66, 065201 (2002)]. The contact interaction is introduced into their model and is found to be necessary for the simultaneous description of g{sub RN{pi}}{sub {pi}} and the {pi}{pi} and {pi}N invariant mass distributions.

Chiral symmetry andN*(1440)→Nππdecay

The N*(1440){yields}N{pi}{pi} decay is studied by making use of the chiral reduction formula. This formula suggests a scalar-isoscalar pion-baryon contact interaction that is absent in the recent study of Hernandez et al. [Phys. Rev. C 66, 065201 (2002)]. The contact interaction is introduced into their model and is found to be necessary for the simultaneous description of g{sub RN{pi}}{sub {pi}} and the {pi}{pi} and {pi}N invariant mass distributions.

Chiral Symmetry and N*(1440) -> N pi pi Decay

The N*(1440){yields}N{pi}{pi} decay is studied by making use of the chiral reduction formula. This formula suggests a scalar-isoscalar pion-baryon contact interaction that is absent in the recent study of Hernandez et al. [Phys. Rev. C 66, 065201 (2002)]. The contact interaction is introduced into their model and is found to be necessary for the simultaneous description of g{sub RN{pi}}{sub {pi}} and the {pi}{pi} and {pi}N invariant mass distributions.