K. Saito

Tokyo University of Science, Edo, Tōkyō, Japan

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Publications (60)169.45 Total impact

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    ABSTRACT: Using the quark–meson coupling (QMC) model, we study the density dependence of the quark and gluon condensates in nuclear matter. We show that the change of the quark condensate is mainly driven by the scalar field in the medium and that the reduction of the quark condensate is suppressed at high density, even in the mean-field approximation. The gluon condensate decreases by 4–6% at nuclear saturation density. We also give a simple relationship between the change of the quark condensate and that of a hadron mass in the medium.
    Modern Physics Letters A 11/2011; 13(10). · 1.11 Impact Factor
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    ABSTRACT: Prompted by the level of accuracy now being achieved in tests of the unitarity of the CKM matrix, we consider the possible modification of the Fermi matrix element for the $\beta$-decay of a neutron, including possible in-medium and isospin violating corrections. While the nuclear modifications lead to very small corrections once the Behrends-Sirlin-Ademollo-Gatto theorem is respected, the effect of the $u-d$ mass difference on the conclusion concerning $V_{ud}$ is no longer insignificant. Indeed, we suggest that the correction to the value of $|V_{ud}|^2 \, + \, |V_{us}|^2 \, + \, |V_{ub}|^2$ is at the level of $10^{-4}$.
    Physics Letters B 01/2011; 696. · 4.57 Impact Factor
  • T. Miyatsu, K. Saito
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    ABSTRACT: The chiral version of the QMC model, in which the effect of gluon and pion exchanges is included self-consistently, is applied to the hyperons in a nuclear medium. The hyperfine interaction due to the gluon exchange plays an important role in the in-medium baryon spectra, while the pion-cloud effect is relatively small. At the quark mean-field level, the $\Lambda$ feels more attractive force than the \Sigma or \Xi in matter.
    03/2009;
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    ABSTRACT: Using the volume coupling version of the cloudy bag model, the quark–meson coupling model is extended to study the role of pion field and the properties of nuclear matter. The extended model includes the effect of gluon exchange as well as the pion-cloud effect, and provides a good description of the nuclear matter properties. The relationship between the extended model and the EFT approach to nuclear matter is also discussed.
    Physics Letters B 07/2008; · 4.57 Impact Factor
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    ABSTRACT: A new approach based on antisymmetrized molecular dynamics is proposed to correctly take account of the many-body correlation. We applied it to the spectra of low-lying, light and strange baryons. The inclusion of the quark-quark correlation is vital to predict the precise spectra, and the semi-relativistic kinematics is also important to correct the level ordering. The baryon spectra calculated by the present method is as precise as the Faddeev calculation.
    Journal of Physics G Nuclear and Particle Physics 06/2008; · 5.33 Impact Factor
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    ABSTRACT: We study the bound nucleon sigma term and the quark condensate in nuclear matter. In the quark-meson coupling (QMC) model the nuclear correction to the sigma term is small and negative, i.e., it decelerates the decrease of the quark condensate in nuclear matter. However, the quark condensate in nuclear matter is controlled primarily by the scalar-isoscalar $\sigma$ field. Compared to the leading term, it moderates the decrease more than that of the nuclear sigma term alone at densities around and larger than the normal nuclear matter density.
    European Physical Journal A 09/2006; · 2.42 Impact Factor
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    ABSTRACT: We review the effect of hadron structure changes in a nuclear medium using the quark-meson coupling (QMC) model, which is based on a mean field description of non-overlapping nucleon (or baryon) bags bound by the self-consistent exchange of scalar and vector mesons. This approach leads to simple scaling relations for the changes of hadron masses in a nuclear medium. It can also be extended to describe finite nuclei, as well as the properties of hypernuclei and meson-nucleus deeply bound states. It is of great interest that the model predicts a variation of the nucleon form factors in nuclear matter. We also study the empirically observed, Bloom-Gilman (quark-hadron) duality. Other applications of the model include subthreshold kaon production in heavy ion collisions, D and D-bar meson production in antiproton-nucleus collisions, and J/Psi suppression. In particular, the modification of the D and D-bar meson properties in nuclear medium can lead to a large J/Psi absorption cross section, which explains the observed J/Psi suppression in relativistic heavy ion collisions.
    Progress in Particle and Nuclear Physics 07/2005; · 2.26 Impact Factor
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    ABSTRACT: We generalize the linear sigma model in order to develop a chiral-invariant model of nuclear structure. The model is natural, and contains not only the usual sigma meson which is the chiral partner of the pion but also a new chiral-singlet that is responsible for the medium-range nucleon-nucleon attraction. This approach provides significant advantages in terms of its description of nuclear matter and finite nuclei in comparison with conventional models based on the linear sigma model. Comment: 12 pages, including 3 tables and 3 figures; preprint number is added
    European Physical Journal A 03/2005; · 2.42 Impact Factor
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    ABSTRACT: Effect of bound nucleon internal structure change on nuclear structure functions is investigated based on local quark–hadron duality. The bound nucleon structure functions calculated for charged-lepton and (anti)neutrino scattering are all enhanced in symmetric nuclear matter at large Bjorken-x (x≳0.85) relative to those in a free nucleon. This implies that a part of the enhancement observed in the nuclear structure function F2 (in the resonance region) at large Bjorken-x (the EMC effect) is due to the effect of the bound nucleon internal structure change. However, the x dependence for the charged-lepton and (anti)neutrino scattering is different. The former (latter) is enhanced (quenched) in the region 0.8≲x≲0.9 (0.7≲x≲0.85) due to the difference of the contribution from axial vector form factor. Because of these differences charge symmetry breaking in parton distributions will be enhanced in nuclei.
    Physics Letters B 09/2004; · 4.57 Impact Factor
  • Annual Review of Nuclear and Particle Science 11/2003; 45:337-390. · 7.40 Impact Factor
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    K. Saito, K. Tsushima
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    ABSTRACT: Using the quark-meson coupling model, we calculate the form factors at sigma- and omega-nucleon strong-interaction vertices in nuclear matter. The Peierls-Yoccoz projection technique is used to take account of center of mass and recoil corrections. We also apply the Lorentz contraction to the internal quark wave function. The form factors are reduced by the nuclear medium relative to those in vacuum. At normal nuclear matter density and Q^2 = 1 GeV^2, the reduction rate in the scalar form factor is about 15%, which is almost identical to that in the vector one. We parameterize the ratios of the form factors in symmetric nuclear matter to those in vacuum as a function of nuclear density and momentum transfer.
    Physics Letters B 08/2003; · 4.57 Impact Factor
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    ABSTRACT: We study the effect of bound nucleon form factors on charged-current neutrino-nucleus scattering. The bound nucleon form factors of the vector and axial-vector currents are calculated in the quark-meson coupling model. We compute the inclusive $^{12}$C($\nu_\mu,\mu^-$)$X$ cross sections using a relativistic Fermi gas model with the calculated bound nucleon form factors. The effect of the bound nucleon form factors for this reaction is a reduction of $\sim$8% for the total cross section, relative to that calculated with the free nucleon form factors. Comment: Latex, 11 pages, 3 figures, version to appear in Phys. Rev. C (Brief Report)
    Physical Review C 07/2003; · 3.72 Impact Factor
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    ABSTRACT: We discuss the electromagnetic form factors, axial form factors, and structure functions of a bound nucleon in the quark-meson coupling (QMC) model. Free space nucleon form factors are calculated using the improved cloudy bag model (ICBM). After describing finite nuclei and nuclear matter in the quark-based QMC model, we compute the in-medium modification of the bound nucleon form factors in the same framework. Finally, limits on the medium modification of the bound nucleon $F_2$ structure function are obtained using the calculated in-medium electromagnetic form factors and local quark-hadron duality.
    02/2003;
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    ABSTRACT: We study both the spin-average and spin-dependent structure functions of the lithium isotopes, $^{6-11}$Li, which could be measured at RIKEN and other nuclear facilities in the future. It is found that the light-cone momentum distribution of the valence neutron in the halo of $^{11}$Li is very sharp and symmetric around y = 1, because of the weak binding. The EMC ratios for Li isotopes are then calculated. We study the possibility of extracting the neutron structure function from data for the nuclear structure functions of the Li isotopes. Next we calculate the spin-dependent structure functions of $^{7,9,11}$Li isotopes, which have spin of 3/2. The effect of the nuclear binding and Fermi motion on the multipole spin structure function, $^{3/2}_{~1}g_1$, is about 10% in the region x < 0.7, but it becomes quite important at large x. The spin structure function of $^{3/2}_{~3}g_1$ is also investigated. Finally, we discuss the modification of the Gottfried and Bjorken integrals in a nuclear medium and point out several candidates for a pair of mirror nuclei to study the flavor-nonsinglet quark distributions in nuclei. Comment: 23 pages + 7 tables + 15 figures
    Nuclear Physics A 10/2001; · 2.50 Impact Factor
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    ABSTRACT: We study shadowing and antishadowing corrections to the flavor nonsinglet structure function F23He-F23H and show that the difference between the one-particle density distributions of 3He and 3H plays an important role at very small x. We find that the flavor nonsinglet structure function in these mirror nuclei is enhanced at small x by nuclear shadowing, which increases the nuclear Gottfried integral, integrated from 10-4 to 3, by 15–41 %. When integrated from zero, the Gottfried integral is divergent for these mirror nuclei. It seems likely that, as a consequence of charge symmetry breaking, this may also apply to the proton-neutron system.
    Physical review D: Particles and fields 08/2001; 64(5).
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    ABSTRACT: Using a pair of the lightest mirror nuclei, 3He and 3H, we study the effect of the medium modification of pion fields on the flavor nonsinglet structure function. The change of the pion fields leads to an enhancement of the flavor asymmetry of the antiquark distributions in a nucleus.
    Physics Letters B 03/2001; · 4.57 Impact Factor
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    ABSTRACT: We study deep inelastic scattering on isospin asymmetric nuclei. In particular, the difference of the nuclear structure functions and the Gottfried sum rule for the lightest mirror nuclei, 3He and 3H, are investigated. It is found that such systems can provide significant information on charge symmetry breaking and flavor asymmetry in the nuclear medium. Furthermore, we propose a new method to extract the neutron structure function from radioactive isotopes far from the line of stability. We also discuss the flavor asymmetry in the Drell–Yan process with isospin asymmetric nuclei.
    Physics Letters B 08/2000; · 4.57 Impact Factor
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    ABSTRACT: We make a detailed study of the effect that the recently predicted modification of the in-medium masses of charmed mesons would have on J/Ψ dissociation on pion and ρ-meson comovers in relativistic heavy ion collisions. We find a substantial dependence of the J/Ψ absorption rates on the density and temperature of the nuclear matter. This suggests that a quantitative analysis of J/Ψ dissociation in nucleus nucleus collisions should include the effects of the modification of meson masses in dense matter.
    Physics Letters B 06/2000; · 4.57 Impact Factor
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    ABSTRACT: We discuss the effect of changes in meson properties in a nuclear medium on physical observables, notably, $J/\Psi$ dissociation on pion and $\rho$ meson comovers in relativistic heavy ion collisions, and the prediction of the $\omega$-, $\eta$- and $\eta'$-nuclear bound states. Comment: 6 pages, 5 Postscript figures, uses espcrc1.sty, 2 talks given by K. Tsushima at the International Conference on Quark Nuclear Physics, Adelaide, February 21-25, 2000, to be published in the Proceedings, Nucl. Phys. A
    05/2000;

Publication Stats

2k Citations
169.45 Total Impact Points

Institutions

  • 2003–2011
    • Tokyo University of Science
      • Department of Fire Science and Technology
      Edo, Tōkyō, Japan
  • 1994–2001
    • University of Adelaide
      • Special Research Centre for the Subatomic Structure of Matter
      Adelaide, South Australia, Australia
  • 1998
    • Sendai National College of Technology
      Sendai, Kagoshima, Japan