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K. Tsushima

Publications and source records attributed to K. Tsushima.

At least 109 records · Page 6Linked to original sources
arXiv2009

Medium modifications of the bound nucleon GPDs and incoherent DVCS on nuclear targets

We study incoherent DVCS on $^4$He in the $^4{\rm He}(e,e^{\prime}γp)X$ reaction, which probes medium-modifications of the bound nucleon GPDs and elastic form factors. Assuming that the bound nucleon GPDs are modified in proportion to the corresponding bound nucleon elastic form factors, as predicted in the Quark-Meson Coupling model, we develop an approach to calculate various incoherent nuclear DVCS observables. As an example, we compute the beam-spin DVCS asymmetry, and predict the $x_B$- and $t$-dependence of the ratio of the bound to free proton asymmetries, $A_{\rm LU}^{p^{\ast}}(ϕ)/A_{\rm LU}^{p}(ϕ)$. We find that the deviation of $A_{\rm LU}^{p^{\ast}}(ϕ)/A_{\rm LU}^{p}(ϕ)$ from unity is as much as $\sim$ 6%.

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arXiv2008

Faddeev calculation of pentaquark $Θ^+$ in the Nambu-Jona-Lasinio model-based diquark picture

A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark $Θ^+$ in the diquark picture of Jaffe and Wilczek in which $Θ^+$ is a diquark-diquark-${\bar s}$ three-body system. Nambu-Jona-Lasinio (NJL) model is used to calculate the lowest order diagrams in the two-body scatterings of ${\bar s}D$ and $D D$. With the use of coupling constants determined from the meson sector, we find that ${\bar s}D$ interaction is attractive in s-wave while $DD$ interaction is repulsive in p-wave. With only the lowest three-body channel considered, we do not find a bound $ \frac 12^+$ pentaquark state. Instead, a bound pentaquark $Θ^+$ with $ \frac 12^-$ is obtained with a unphysically strong vector mesonic coupling constants.

hep-ph↗
arXiv2008

Quark-meson coupling model with the cloudy bag

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.

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arXiv2008

Simulation of symmetric nuclei and the role of Pauli potential in binding energies and radii

It is shown that the use of a density dependent effective Pauli potential together with a nucleon-nucleon interaction potential plays a crucial role to reproduce not only the binding energies but also the matter root mean square radii of medium mass range spin-isospin saturated nuclei. This study is performed with a semiclassical Monte Carlo many-body simulation within the context of a simplified nucleon-nucleon interaction to focus on the effect of the genuine correlations due to the fermionic nature of nucleons. The procedure obtained is rather robust and it does not depend on the detailed features of the nucleon-nucleon interaction. For nuclei below saturation the density dependence may be represented in terms either of the nucleon number, $A$, or the associated Fermi momenta. When testing the simulation procedure for idealized "infinite" symmetric nuclear matter within the corresponding range of densities, it turns out that finite size effects affect the Pauli potential strength parametrization in systems up to about 120 particles while remaining approximately stable for larger systems.

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arXiv2008

Binding energies and modelling of nuclei in semiclassical simulations

We study the binding energies of spin-isospin saturated nuclei with nucleon number $8 \le A \le 100$ in semiclassical Monte Carlo many-body simulations. The model Hamiltonian consists of, (i) nucleon kinetic energy, (ii) a nucleon-nucleon interaction potential, and (iii) an effective Pauli potential which depends on density. The basic ingredients of the nucleon-nucleon potential are, a short-range repulsion, and a medium-range attraction. Our results demonstrate that one can always expect to obtain the empirical binding energies for a set of nuclei by introducing a proper density dependent Pauli potential. The present work suggests a simple, pragmatic procedure for modelling a set of nuclei calibrated by the empirical binding energies for a given NN interaction potential. Then, each set of modelled nuclei can be tested by studying other properties of nuclei in semiclassical simulations.

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arXiv2007

A Faddeev Calculation for Pentaquark $Θ^+$ in Diquark Picture with Nambu-Jona-Lasinio Type Interaction

A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark $Θ^+$ in the diquark picture of Jaffe and Wilczek in which $Θ^+$ is a diquark-diquark-${\bar s}$ three-body system. Nambu-Jona-Lasinio (NJL) model is used to calculate the lowest order diagrams in the two-body scatterings of ${\bar s}D$ and $D D$. With the use of coupling constants determined from the meson sector, we find that ${\bar s}D$ interaction is attractive while $DD$ interaction is repulsive, and there is no bound $\frac 12^+$ pentaquark state. A bound pentaquark $Θ^+$ can only be obtained with unphysically strong vector mesonic coupling constants.

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arXiv2006

Nucleon sigma term and quark condensate in nuclear matter

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 $σ$ 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.

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arXiv2006

Dynamical study of ${\bf QQ-\bar u \bar d}$ mesons

It has been recently conjectured by Selem and Wilczek \cite{Sel06} the existence of a $ss-[\bar u \bar d]$ meson due to strong correlations between the two light antiquarks. We make a detailed study of this system within a dynamical quark model which has proven to be successful in reproducing the most important features of low-energy hadron phenomenology. Our results, obtained within a parameter-free calculation, show that the antidiquark component of the $ss \bar u \bar d$ system indeed entails the stronger attraction, and drives its energy much lower than the $\bar{N}Ξ$ threshold, but still above the $\bar{K^0} {K^*}^-$ or $\bar{{K^*}^0} K^-$ thresholds. We have also studied the $cc \bar u \bar d$ and $bb \bar u \bar d$ systems. Exotic mesons are only expected to exist in the limit of large mass for the two-quark subsystem, $bb\bar u \bar d$, since the calculated mass is below the $\bar{B^0} {B^*}^-$ or $\bar{{B^*}^0} B^-$ thresholds.

hep-ph↗
arXiv2005

Nucleon and hadron structure changes in the nuclear medium and impact on observables

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.

hep-ph↗
arXiv2005

Two-scale scalar mesons in nuclei

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.

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arXiv2005

Effect of bound nucleon internal structure change on nuclear structure functions

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-$x$ ($x \agt 0.85$) relative to those in a free nucleon. This implies that a part of the enhancement observed in the nuclear structure function $F_2$ (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 $0.8 \alt x \alt 0.9$ [$0.7 \alt x \alt 0.85$] 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.

hep-ph↗
arXiv2004

A QCD Sum Rule Study of $Θ^+$ in Nuclear Matter

We consider a $[ud]^2\bar{s}$ current, in the finite-density QCD sum rule approach, to investigate the scalar and vector self-energies of the recently observed pentaquark state $Θ^+(1540)$, propagating in nuclear mater. We find that, opposite to what was obtained for the nucleon, the vector self-energy is negative, and the scalar self-energy is positive. There is a substantial cancellation between them resulting in an attractive net self-energy of the same order as in the nucleon case.

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arXiv2004

$Λ^+_c$, $Σ_c$, $Ξ_c$ and $Λ_b$ hypernuclei in the quark-meson coupling model

Charmed (and bottom) hypernuclei are studied in the quark-meson coupling (QMC) model. This completes systematic studies of charmed ($Λ_c^+, Σ_c, Ξ_c$), and $Λ_b$ hypernuclei in the QMC model. Effects of the Pauli blocking due to the underlying quark structure of baryons, and the $Σ_c N - Λ_c N$ channel coupling are phenomenologically taken into account at the hadronic level in the same way as those included for strange hypernuclei. Our results suggest that the $Σ_c^{++}$ and $Ξ_c^+$ hypernuclei are very unlikely to be formed, while the $Λ_c^+$, $Ξ_c^0$ and $Λ_b$ hypernuclei are quite likely to be formed. For the $Σ_c^+$ hypernuclei, the formation probability is non-zero though small. A detailed analysis is also made about the phenomenologically introduced Pauli blocking and channel coupling effects for the $Σ_c^0$ hypernuclei.

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arXiv2004

Effect of the bound nucleon form factors on charged-current neutrino-nucleus scattering

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($ν_μ,μ^-$)$X$ 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.

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arXiv2004

Quark Distributions in a Medium

We derive the formal expressions needed to discuss the change of the twist-two parton distribution functions when a hadron is placed in a medium with relativistic scalar and vector mean fields

hep-ph↗
arXiv2003

Determination of the $Θ^+$ parity from $γn \to K^- K^+ n$

It is demonstrated that measurements of photon asymmetry in the $γn \to K^- K^+ n$ reaction, can most likely determine the parity of the newly discovered $Θ^+$ pentaquark. We predict that if the parity of $Θ^+$ is positive, the photon asymmetry is significantly positive; if the parity is negative, the photon asymmetry is significantly negative. If the background contribution is large, the photon asymmetry may become very small in magnitude, thereby making it difficult to distinguish between the positive and negative parity results. However, even in this case, a combined analysis of the $(K^+ n)$ invariant mass distribution and photon asymmetry should allow a determination of the parity of $Θ^+$.

hep-ph↗
arXiv2003

Scalar and vector form factors of the in-medium nucleon

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.

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