K. Saito

J-PARC Center, Ibaragi, Ōsaka, Japan

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Publications (66)217.58 Total impact

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    M. Hirai · S. Kumano · K. Saito · T. Watanabe
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    ABSTRACT: A clustering aspect is explained for the $^9$Be nucleus in charged-lepton deep inelastic scattering. Nuclear modifications of the structure function $F_2$ are studied by the ratio $R_{\rm EMC} = F_2^A /F_2^D$, where $A$ and $D$ are a nucleus and the deuteron, respectively. In a JLab experiment, an unexpectedly large nuclear modification slope $|dR_{\rm EMC}/dx|$ was found for $^9$Be, which could be related to its clustering structure. We investigated a mean conventional part of a nuclear structure function $F_2^A$ by a convolution description with nucleon momentum distributions calculated by antisymmetrized (or fermionic) molecular dynamics (AMD) and also by a simple shell model. We found that clustering effects are small in the conventional part, so that the JLab result could be associated with an internal nucleon modification or a short-range nuclear correlation which is caused by high densities due to cluster formation.
    Preview · Article · Aug 2014 · Journal of Physics Conference Series
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    K. Saito · K. Tsushima · A. W. Thomas

    Full-text · Dataset · Jun 2014
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    ABSTRACT: The nucleon form factors in free space are usually thought to be modified when a nucleon is bound in a nucleus or immersed in a nuclear medium. We investigated effects of the density-dependent axial and weak-vector form factors on the electro-neutrino (ve) and anti-electro-neutrino (v̄e) reactions with incident energy Ev ≤ 80 MeV via neutral current (NC) and charged current (CC) for a nucleon in a nuclear medium or 12C. For the density-dependent form factors, we exploited the quark-meson-coupling (QMC) model, and apply them to the v̄e and v̄e induced reactions by NC and CC. In CC reaction, about 5 % decrease of the electro neutrino (v̄e) reaction cross section on the nucleon is shown to be occurred in normal density, ρ=ρ0∼0.15fm- 3, and also about 5 % reduction of total v̄e cross section on 12C is obtained by the modification of the weak form factors for bound nucleons. Density effects for both cases are relatively small, but they are as large as the effect by the Coulomb distortion of outgoing leptons in the ν-reaction. However, density effects in the anti-electro neutrino (v̄e) reaction reduced significantly about 30 % the cross sections for both the nucleon and 12C cases. For NC, about 12 % decrease of the total cross section by the v̄e reaction on the nucleon is obtained at normal density, ρ=ρ0∼0.15fm-3, as well as about 18 % reduction of the total v̄e cross section on 12C, by the modification of the weak form factors of the bound nucleon. However, similarly to the CC reaction, effects of the nucleon property change in the v̄e reaction reduce significantly the cross sections about 30 % for the nucleon in matter and 12C cases. In this talk, we address that such a large asymmetry in the v̄e cross sections in both reactions is originated from the different helicities of v̄e and v̄e.
    Full-text · Article · Jan 2014 · AIP Conference Proceedings
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    ABSTRACT: Next generation neutrino oscillation experiments will need a quantitative understanding of neutrino-nucleus interaction far better than ever. Kinematics covered by the relevant neutrino-nucleus interaction spans wide region, from the quasi-elastic, through the resonance region, to the deeply inelastic scattering region. The neutrino-nucleus interaction in each region has quite different characteristics. Obviously, it is essential to combine different expertise to construct a unified model that covers all the kinematical region of the neutrino-nucleus interaction. Recently, several experimentalists and theorists got together to form a collaboration to tackle this problem. In this contribution, we report the collaboration’s recent activity and a goal in near future.
    No preview · Article · Mar 2013
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    K.saito · K.tsushima · A. W.thomas
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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.
    Full-text · Article · Nov 2011 · Modern Physics Letters A
  • T.watanabe · S.oryu · K.saito
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    ABSTRACT: Proposed a new method which is suitable for systematic calculations in few-body systems, we call it the Jacobi-coordinate-basis antisymmetrized molecular dynamics (JAMD). We show good abilities of the method by demonstrating some examples in atoms, molecules, nuclei, and baryons systems.
    No preview · Article · Nov 2011 · Modern Physics Letters A
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    M Hirai · H Kawamura · S. Kumano · K Saito
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    ABSTRACT: We report recent studies on structure functions of the nucleon and nuclei. First, clustering effects are investigated in the structure function F_2 of Be-9 for explaining an unusual nuclear correction found in a JLab experiment. We propose that high densities created by formation of clustering structure like 2*alpha+neutron in Be-9 is the origin of the unexpected JLab result by using the antisymmetrized molecular dynamics (AMD). There is an approved proposal at JLab to investigate the structure functions of light nuclei including the cluster structure, so that much details will become clear in a few years. Second, tensor-polarized quark and antiquark distributions are obtained by analyzing HERMES measurements on the structure function b_1 for the deuteron. The result suggests a finite tensor polarization for antiquark distributions, which is an interesting topic for further theoretical and experimental investigations. An experimental proposal exists at JLab for measuring b_1 of the deuteron as a new tensor-structure study in 2010's. Furthermore, the antiquark tensor polarization could be measured by polarized deuteron Drell-Yan processes at hadron facilities such as J-PARC and GSI-FAIR. Third, the recent CDF dijet anomaly is investigated within the standard model by considering possible modifications of the strange-quark distribution. We find that the shape of a dijet-mass spectrum changes depending on the strange-quark distribution. It indicates that the CDF excess could be partially explained as a PDF effect, particularly by the strangeness in the nucleon, within the standard model if the excess at m_{jj}~140 GeV is not a sharp peak.
    Preview · Article · Nov 2011
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    M Hirai · S. Kumano · K Saito · T Watanabe
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    ABSTRACT: An anomalous nuclear modification was reported by JLab measurements on the beryllium-9 structure function F_2. It is unexpected in the sense that a nuclear modification slope is too large to be expected from its average nuclear density. We investigated whether it is explained by a nuclear clustering configuration in Be-9 with two \alpha nuclei and surrounding neutron clouds. Such clustering aspects are studied by using antisymmetrized molecular dynamics (AMD) and also by a simple shell model for comparison. We consider that nuclear structure functions F_2^A consist of a mean conventional part and a remaining one depending on the maximum local density. The first mean part does not show a significant cluster effect on F_2. However, we propose that the remaining one could explain the anonymous JLab slope, and it is associated with high densities created by the cluster formation in Be-9. The JLab measurement is possibly the first signature of clustering effects in high-energy nuclear reactions. A responsible physics could be an internal nucleon modification, which is caused by the high densities due to the cluster configuration.
    Preview · Article · Mar 2011
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    M Hirai · S. Kumano · K Saito
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    ABSTRACT: We report current status of global analyses on nuclear parton distribution functions (NPDFs). The optimum NPDFs are determined by analyzing high-energy nuclear reaction data. Due to limited experimental measurements, antiquark modifications have large uncertainties at x>0.2 and gluon modifications cannot be determined. A nuclear modification difference between u and d quark distributions could be an origin of the long-standing NuTeV sin^2 theta_w anomaly. There is also an issue of nuclear modification differences between the structure functions of charged-lepton and neutrino reactions. Next, nuclear clustering effects are discussed in structure functions F_2^A as a possible explanation for an anomalous result in the Be-9 nucleus at the Thomas Jefferson National Accelerator Facility (JLab). Last, tensor-polarized quark and antiquark distribution functions are extracted from HERMES data on the polarized structure function b_1 of the deuteron, and they could be used for testing theoretical models and for proposing future experiments, for example, the one at JLab. Such measurements could open a new field of spin physics in spin-one hadrons.
    Preview · Article · Feb 2011
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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 $10^{-4}$.
    Full-text · Article · Jan 2011 · Physics Letters B
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    M Hirai · S. Kumano · K Saito · T Watanabe
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    ABSTRACT: For understanding an anomalous nuclear effect experimentally observed for the beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility (JLab), clustering aspects are studied in structure functions of deep inelastic lepton-nucleus scattering by using momentum distributions calculated in antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple shell model for comparison. According to the AMD, the Be-9 nucleus consists of two alpha-like clusters with a surrounding neutron. The clustering produces high-momentum components in nuclear wave functions, which affects nuclear modifications of the structure functions. We investigated whether clustering features could appear in the structure function F_2 of Be-9 along with studies for other light nuclei. We found that nuclear modifications of F_2 are similar in both AMD and shell models within our simple convolution description although there are slight differences in Be-9. It indicates that the anomalous Be-9 result should be explained by a different mechanism from the nuclear binding and Fermi motion. If nuclear-modification slopes d(F_2^A/F_2^D)/dx are shown by the maximum local densities, the Be-9 anomaly can be explained by the AMD picture, namely by the clustering structure, whereas it certainly cannot be described in the simple shell model. This fact suggests that the large nuclear modification in Be-9 should be explained by large densities in the clusters. For example, internal nucleon structure could be modified in the high-density clusters. The clustering aspect of nuclear structure functions is an unexplored topic which is interesting for future investigations.
    Preview · Article · Aug 2010 · Physical Review C
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    M Hirai · S. Kumano · K Saito
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    ABSTRACT: We explain the current status of nuclear parton distribution functions in connection with neutrino‐nucleus interactions. Neutrino deep inelastic scattering (DIS) measurements have been done for heavy nuclear targets such as iron and lead. In order to extract structure functions of the nucleon, one needs to remove nuclear effects from the data. However, recent studies indicate that there are inconsistencies in nuclear modifications between charged‐lepton and neutrino scattering measurements. Nuclear medium effects could be also an origin for the NuTeV anomaly in the weak‐mixing angle. In addition, the modifications could affect neutrino‐oscillation experiments because some DIS events of neutrino‐oxygen nucleus interactions are contained. On the other hand, the nuclear medium effects themselves are interesting and important for describing nuclei in terms of quark and gluon degrees of freedom.
    Preview · Article · Sep 2009
  • T. Watanabe · S. Oryu · K. Saito
    [Show abstract] [Hide abstract]
    ABSTRACT: Proposed a new method which is suitable for systematic calculations in few-body systems, we call it the Jacobi-coordinate-basis antisymmetrized molecular dynamics (JAMD). We show good abilities of the method by demonstrating some examples in atoms, molecules, nuclei, and baryons systems.
    No preview · Article · Apr 2009
  • 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.
    No preview · Article · Mar 2009
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    S. Nagai · T. Miyatsu · K. Saito · K. Tsushima
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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.
    Full-text · Article · Jul 2008 · Physics Letters B
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    T Watanabe · M. Oosawa · K Saito · S. Oryu
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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.
    Preview · Article · Jun 2008 · Journal of Physics G Nuclear and Particle Physics
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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.
    Full-text · Article · Sep 2006 · European Physical Journal A
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    K. Saito · K. Tsushima · A. W. Thomas
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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.
    Full-text · Article · Jul 2005 · Progress in Particle and Nuclear Physics
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    K. Saito · H. Kouno · K. Tsushima · A. W. Thomas
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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
    Full-text · Article · Mar 2005 · European Physical Journal A
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    K. Tsushima · K. Saito · F.M. Steffens
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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.
    Full-text · Article · Sep 2004 · Physics Letters B

Publication Stats

2k Citations
217.58 Total Impact Points

Institutions

  • 2014
    • J-PARC Center
      Ibaragi, Ōsaka, Japan
  • 2003-2011
    • Tokyo University of Science
      • Department of Fire Science and Technology
      Edo, Tōkyō, Japan
  • 1996-2000
    • University of Adelaide
      • Special Research Centre for the Subatomic Structure of Matter
      Tarndarnya, South Australia, Australia
  • 1998
    • Sendai National College of Technology
      Sendai, Kagoshima, Japan