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A. Hosaka

Publications and source records attributed to A. Hosaka.

At least 73 records · Page 4Linked to original sources

Coupling of \bar K*N to the Lambda(1520)

We study the coupling of the Lambda(1520)= Lambda* resonance to the \bar K* vector meson and nucleon. This coupling is not directly measured from the resonance decay, but is expected to be important in hyperon production reactions, in particular for the exotic Theta+ production. We compute the coupling in two different schemes, one in the chiral unitary model where the Lambda* is dominated by the quasibound state of mesons and baryons, and the other in the quark model where the resonance is a p-wave excitation in the three valence quarks. Although it is possible to construct both models such that they reproduce the \bar K N and pi Sigma decays, there is a significant difference between the Lambda* \bar K* N couplings in the two models. In the chiral unitary model $|g_{Λ^*\bar{K}^* N}| \sim 1.5$, while in the quark model $|g_{Λ^*\bar{K}^* N}| \sim 10$. The difference of the results stems from the different structure of the Lambda* in both models, and hence, an experimental determination of this coupling would shed light on the nature of the resonance.

hep-ph↗

The mass of the nucleon in a chiral quark-diquark model

The mass of the nucleon is studied in a chiral quark-diquark model. Both scalar and axial-vector diquarks are taken into account for the construction of the nucleon state. After the hadronization procedure to obtain an effective meson-baryon Lagrangian, the quark-diquark self-energy is calculated in order to generate the baryon kinetic term as well as the mass of the nucleon. It turns out that both the scalar and axial-vector parts of the self-energy are attractive for the mass of the nucleon. We investigate the range of parameters that can reproduce the mass of the nucleon.

hep-ph↗

Five-body calculation of resonance and scattering states of pentaquark system

Scattering problem of the $uudd{\bar s}$ system, in the standard non-relativistic quark model of Isgur-Karl, is solved for the first time, by treating the large five-body modelspace including the $NK$ scattering channel accurately with the Gaussian expansion method and the Kohn-type coupled-channel variational method. The two-body interaction that reproduces observed properties of ordinary baryons and mesons is applied to the pentaquark system with no additional adjustable parameter. The five-body wave function calculated has the correct asymptotic form in its the scattering-channel component and describes $qq$ and $q{\bar q}$ correlations properly. The $NK$ scattering phase shift calculated shows no resonance in the energy region of the reported pentaquark $Θ^+(1540)$, that is, at 0-500 MeV above the $NK$ threshold ($1.4-1.9$ GeV in mass). The phase shift does show two resonances just above 500 MeV: a broad ${1/2}^+$ resonance with a width of $ Γ\sim~110$ MeV located at $\sim~520$ MeV ($\sim~2.0$ GeV in mass) and a sharp ${1/2}^-$ resonance with $Γ=$0.12 MeV at 540 MeV. Properties of these states are discussed.

hep-ph↗

Relation between the separable and one-boson-exchange potential for the covariant Bethe-Salpeter equation

We investigate the relation between the rank I separable potential for the covariant Bethe-Salpeter equation and the one-boson-exchange potential. After several trials of the parameter choices, it turns out that it is not always possible to reproduce the phase-shifts calculated from a single term of the one-boson-exchange potential especially of the $σ$-exchange term, separately by the rank I separable potential. Instead, it is shown that the separable potential is useful to parameterize the total nucleon-nucleon interaction.

nucl-th↗

Decay of Theta+ in a quark model

We study the decay of Theta+ in a non-relativistic quark model. The wave function of Theta+ is constructed for the two cases JP = 1/2+- as products of color, spin, flavor and orbital parts respecting total antisymmetrization among the four quarks. We find that for the negative parity Theta+ the width becomes very large which is of order of several hundreds MeV, while it is about a several tens MeV for the positive parity. By assuming additionally diquark correlations, the width is reduced to be of order 10 MeV. It is also pointed out that a similar calculation for 3/2- results in strong suppression of its width.

hep-ph↗

Two-meson cloud contribution to the baryon antidecuplet binding

We study the two-meson virtual cloud contribution to the self-energy of the SU(3) antidecuplet, to which the Theta+ pentaquark is assumed to belong. This is motivated by the large branching ratio of the N(1710) decay into two pions and one nucleon. We derive effective Lagrangians that describe the N(1710) decay into N-pi-pi with two pions in s or p wave. We obtain increased binding for all members of the antidecuplet and a contribution to the mass splitting between states with different strangeness which is at least 20 % of the empirical one. We also provide predictions for three-body decays of the pentaquark antidecuplet.

hep-ph↗

Dynamical baryon resonances from chiral unitarity

We report on the latests developments in the field of baryonic resonances generated from the meson-baryon interaction in coupled channels using a chiral unitary approach. The collection of resonances found in different strangeness and isospin sectors can be classified into SU(3) multiplets. The Lambda(1405) emerges as containing the effect of two poles of the scattering amplitude and various reactions that might preferentially select one or the other pole are discussed.

nucl-th↗

Two-meson cloud contribution to the baryon antidecuplet self-energy

We study the self-energy of the SU(3) antidecuplet coming from two-meson virtual clouds. Assuming that the exotic Theta+ belongs to an antidecuplet representation with N(1710) as nucleon partner, we derive effective Lagrangians that describe the decay of N(1710) into N pi pi with two pions in s- or p-wave. It is found that the self-energies for all members of the antidecuplet are attractive, and the larger strangeness particle is more bound. From two-meson cloud, we obtain about 20 % of the empirical mass splitting between states with different strangeness.

hep-ph↗

Determining the $Θ^+$ quantum numbers through a Kaon induced reaction

We study the $K^+p\to π^+KN$ reaction with kinematical condition suited to the production of the $Θ^+$ resonance. It is shown that in this reaction with the polarization experiment, a combined consideration of the strength at the peak and the angular dependence of cross section can help determine the $Θ^+$ quantum numbers.

nucl-th↗

Chiral symmetry breaking and stability of strangelets

We discuss the stability of strangelets by considering dynamical chiral symmetry breaking and confinement. We use a $U(3)_{L} \times U(3)_{R}$ symmetric Nambu--Jona-Lasinio model for chiral symmetry breaking supplemented by a boundary condition for confinement. It is shown that strangelets with baryon number $A < 2 \times 10^{3}$ can stably exist. For the observables, we obtain the masses and the charge-to-baryon number ratios of the strangelets. These quantities are compared with the observed data of the exotic particles.

hep-ph↗

Hadronic aspects of exotic baryons

In this talk I look into three different topics, addressing first the possibility that the $Θ^+$ is a bound state of $K πN$, exploiting the results of this study to find out the contribution of two meson and one baryon components in the baryon antidecuplet and in the third place I present results on a new resonant exotic baryonic state which appears as dynamically generated by the Weinberg Tomozawa $ΔK$ interaction.

nucl-th↗

Comment on the $Θ^+$-production at high energy

We show that the cross sections of the $Θ^+$-pentaquark production in different processes decrease with energy faster than the cross sections of production of the conventional three-quark hyperons. Therefore, the threshold region with the initial energy of a few GeV or less seemsto be more favorable for the production and experimental study of $Θ^+$-pentaquark.

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Structure and production of Theta+

We study properties of the pentaquark particle Theta+ with emphasis on the role of chiral symmetry. It is shown that when chiral force is sufficiently strong, the positive parity Theta+ may be realized with a lower mass relative to the negative parity state. The decay width is then studied in the non-relativistic quark model. It is shown that the narrow width may be realized for the positive parity state, while the seemingly lowest negative parity state couples strongly to the continuum state resulting in a very broad width. Finally, Theta+ production is studied in photo-induced and proton-induced processes. The polarized proton reaction provides a model independent method to determine the parity of Theta+.

hep-ph↗

Detailed Analysis of the Chiral Unitary Model for Meson-Baryon Scattering with Flavor SU(3) Breaking Effects

We study s-wave meson-baryon scattering using the chiral unitary model. We consider $1/2^{-}$ baryon resonances as quasibound states of the low lying mesons ($π,K,η$) and baryons ($N,Λ,Σ,Ξ$). In previous works, the subtraction constants which appear in loop integrals were found to largely depend on the channels, and it was necessary to fit these constants to reproduce the data. In order to extend this model to all channels with fewer parameters, we introduce flavor SU(3) breaking interactions in the framework of chiral perturbation theory. It is found, however, that the observed SU(3) breaking in meson-baryon scattering cannot be explained by the present SU(3) breaking interactions. The role and importance of the subtraction constants in the present framework are discussed.

nucl-th↗

On the determination of $Θ^+$ quantum numbers and other topics of exotic baryons

In this talk I look into three different topics, addressing first a method to determine the quantum numbers of the $Θ^+$, then exploiting the possibility that the $Θ^+$ is a bound state of $K πN$ and in the third place I present results on a new resonant exotic baryonic state which appears as dynamically generated by the Weinberg Tomozawa $ΔK$ interaction.

hep-ph↗

Photoproduction of $K^*$ for the study of $Λ(1405)$

The photo-induced $K^*$ vector meson production is investigated for the study of the $Λ(1405)$ resonance. This reaction is particularly suited to the isolation of the second pole in the $Λ(1405)$ region which couples dominantly to the $\bar K N$ channel. We obtain the mass distribution of the $Λ(1405)$ which peaks at 1420 MeV, and differs from the nominal one. Combined with several other reactions, like the $π^- p \to K^0 πΣ$ which favours the first pole, this detailed study will reveal a novel structure of the $Λ(1405)$ state.

nucl-th↗

Study of $Λ(1405)$ in photoproduction of $K^*$

We investigate the photoproduction of $K^*$ vector meson for the study of the $Λ(1405)$ resonance. The invariant mass distribution of $πΣ$ shows a different shape from the nominal one, peaking at 1420 MeV. This is considered as a consequence of the double pole structure of $Λ(1405)$, predicted in the chiral unitary model. Combined with other reactions, such as $π^- p \to K^0 πΣ$, experimental confirmation of this fact will reveal a novel structure of the $Λ(1405)$ state.

nucl-th↗

Production of the pentaquark $Θ^+$ in $np$ scattering

We study $np\to ΛΘ^{+}$ and $np\to Σ^{0}Θ^{+}$ processes for both of the positive and negative parities of the $Θ^{+}$. Employing the effective chiral Lagrangians for the $KNY$ and $K^*NY$ interactions, we calculate differential cross sections as well as total cross sections for the $np\to Σ^0 Θ^+$ and $np\to ΛΘ^+$ reactions. The total cross sections for the positive-parity $Θ^+$ turn out to be approximately ten times larger than those for the negative parity $Θ^+$ in the range of the CM energy $\sqrt{s}_{\rm th}\le \sqrt{s}\le 3.5 {\rm GeV}$. The results are rather sensitive to the mechanism of $K$ exchanges in the $t$ -- channel.

hep-ph↗