arXiv subjects

Atsushi Hosaka

Publications and source records attributed to Atsushi Hosaka.

At least 163 records · Page 9Linked to original sources

arXiv2007

Test of the reaction mechanism for gamma N -> K Lambda(1520) using the polarized photon

We study the reaction mechanism for the photoproduction of the Lambda(1520), based on an effective Lagrangian approach. We investigate each contribution of the s-, u-, t-channel processes and contact term, separately. One of the most characteristic features of this reaction is the contact-term dominance which governs the photoproduction from the proton, when the K*-exchange contribution is possibly not too large. We suggest several different ways of the polarizations and arrangement of the beam and target to make to understand the role of each contribution separately in future experiments.

hep-ph↗

arXiv2006

Chiral dynamics and s-wave exotic hadrons

Based on chiral dynamics, existence of exotic hadrons is discussed in the SU(3) symmetric limit. The low energy s-wave interaction of the Nambu-Goldstone boson with a hadron is known to be determined model-independently, which has been used to generate some hadron resonances in nonexotic channels. We show that this interaction in any exotic channels is not strong enough to generate a bound state.

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arXiv2006

Roper resonance in a quark-diquark model

We discuss a new description for the Roper resonance, the first nucleon excited state of JP = 1/2+, in a model of strong diquark correlations. Treating the scalar-isoscalar and axial-vector--isovector diquarks as independent degrees of freedom, two states having nucleon quantum numbers are constructed. Due to the scalar and axial-vector nature of the diquarks, the two nucleon states have different internal structure of spin and isospin. This yields the mass splitting of order several hundreds MeV, and hence the two states are identified with the nucleon and Roper. We demonstrate this scenario in a simple two channel problem.

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arXiv2006

Exotic hadrons in s-wave chiral dynamics

We study s-wave scattering of a hadron and a Nambu-Goldstone boson induced by the model-independent low energy interaction in the flavor SU(3) symmetric limit. Establishing the general structure of the low energy interaction based on group theoretical arguments, we find that the interaction in the exotic channels are in most cases repulsive, and that for possible attractive channels the interaction strengths are weak and uniquely given independent of channel. Solving the scattering problem with this interaction, we show that the attraction in the exotic channels is not strong enough to generate a bound state from the physically known target hadrons. We also find that there are no attractive interaction in the exotic channels in large Nc limit.

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arXiv2006

Exotic Tetraquark ud bar[s] bar[s] of J^P=0^+ in the QCD Sum Rule

We study a QCD sum rule analysis for an exotic tetraquark ud bar[s] bar[s] of J^P=0^+ and I = 1. We construct q q bar[q] bar[q] currents in a local product form and find that there are five independent currents for this channel. Due to high dimensional nature of the current, it is not easy to form a good sum rule when using a single current. This means that we do not find any sum rule window to extract reliable results, due to the insufficient convergence of the OPE and to the exceptional important role of QCD continuum. Then we examine sum rules by using currents of linear combinations of two currents among the independent ones. We find two reasonable cases that predict a mass of the tetraquark around 1.5 GeV.

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arXiv2006

Isospin symmetry breaking of K and K* mesons

We use the method of QCD sum rules to investigate the isospin symmetry breaking of K and K* mesons. The electromagnetic effect, difference between up and down current-quark masses and difference between up and down quark condensates are important. We perform sum rule analyses of their masses and decay constant differences, which are consistent with experimental values. Our results yield Delta f_K = f_{K^0} - f_{K^\pm} = 1.5 MeV.

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arXiv2006

Pentaquark Theta^+ production via gamma N ->K^*bar Theta^+(3/2^(+-))

We study the photoproduction of the exotic pentaquark Theta^+ baryon with the vector kaon, assuming that the quantum numbers of the Theta^+ to be J^P=3/2^(+-) and J^P=1/2^+. Scalar meson kappa(800)-exchange is also taken into account. In contrast with the gamma N -> Kbar Theta^+(3/2^(+-)) process, the large suppression from the proton target is not observed in the total cross sections. We also suggest a method to determine which meson exchange is the most dominant by analyzing the polarizations of incident photon and outgoing K^*. We find that kappa-exchange turns out to be prominent when the polarizations of the photon and K^* are aligned to be parallel, whereas K-exchange does when they are perpendicular to each other.

hep-ph↗

arXiv2006

The leading-twist pion and kaon distribution amplitudes from the QCD instanton vacuum

We investigate the leading-twist light-cone distribution amplitudes for the pion and kaon, based on the nonlocal chiral quark model from the instanton vacuum. Effects of explicit flavor SU(3)-symmetry breaking are taken into account. The Gegenbauer moments are computed, analyzed and compared with those of other models. The one-loop QCD evolution of the moments is briefly discussed. The transverse momentum distributions are also discussed for the pion and kaon light-cone wave functions.

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arXiv2006

Phenomenological study for the Theta+ and two-meson coupling

We examine several assignments of spin and parity for the pentaquark Theta+ state (J^P=1/2^{+,-}, 3/2^{+,-}) in connection with phenomenology of known baryon resonances, using a general framework based on the flavor symmetry. Assuming that the Theta+ belongs to an antidecuplet representation which mixes with an octet, we calculate the mass spectra of the flavor partners of the Theta+ based on the SU(3) symmetry. The decay widths of the Theta+ and nucleon partners are analyzed for the consistency check of the mixing angle obtained from the masses. It is found that a suitable choice of the mixing angle successfully reproduces the observed masses of exotics, when their spin and parity are assigned to be J^P=3/2^-, together with other nonexotic resonances of J^P=3/2^-. The decay widths of Theta -> KN, N(1520) -> pi N, and N(1700) -> pi N are also reproduced simultaneously. We then evaluate two-meson couplings of Theta+, using experimental information of nucleon partners decaying into pi pi N channels, in which the two pions are in scalar- and vector-type correlations. We examine two assignments of spin and parity J^P=1/2^+ and 3/2^-, for which the experimental spectra of known resonances with exotic baryons are properly reproduced by an octet-antidecuplet representation mixing scheme. Using the obtained coupling constants, total cross sections of the reactions pi- p -> K- Theta+ and K+ p -> pi+ Theta+ are calculated. Substantial interference of two terms may occur in the reaction processes for the J^P=1/2^+ case, whereas the interference effect is rather small for the 3/2^- case.

hep-ph↗

arXiv2006

A new $N^*(1675)$ resonance in the $γN\toηN$ reaction

We study the $η$-photoproduction focusing on the new nucleon resonance which was observed at $\sqrt{s}=1675$ MeV with a narrow decay width ($\sim 10$ MeV) in the recent GRAAL experiment. Using an effective Lagrangian approach, we compute differential cross sections for the $η$-photoproduction. In addition to $N^*(1675)$, we employ three other nucleon resonances, i.e. $N^*(1535)$, $N^*(1650)$ and $N^*(1710)$, and vector meson exchanges which are the most relevant ones to this reaction process. As a result, we can reproduce the GRAAL data qualitatively well and observe obvious isospin asymmetry between the transition magnetic moments of $N^*(1675)$: $μ_{γnn^*}\ggμ_{γpp^*}$.

hep-ph↗

arXiv2006

Two Nucleon-States in a Chiral Quark-Diquark Model

We study the ground and first excited states of nucleons in a chiral quark-diquark model. We include two quark-diquark channels of the scalar-isoscalar and axial-vector-isovector types for the nucleon states. The diquark correlation violating the spin-flavor SU(4)$_{SF}$ symmetry allows to treat the two quark-diquark channels independently. Hence the two states appear as the superpositions of the two quark-diquark channels; one is the nucleon and the other is a state which does not appear in the SU(4)$_{SF}$ quark models. With a reasonable choice of model parameters, the mass of the excited state appears at around 1.5 GeV, which we identify with the Roper resonance N(1440).

hep-ph↗

arXiv2005

The Nucleon and Roper Resonance in a Chiral Quark Diquark Model

A description of the nucleon and Roper resonance in a quark-diquark approach is presented. We show that two states with the quantum number of the nucleon can appear in the ground state of the spatial configuration, when there are two types of diquarks: scalar-isoscalar and axial-vector-isovector diquarks. The mass difference between the two states is generated by the mass difference between the two diquarks, which is due to the spin-spin interaction between the two quarks in the diquarks. The two states are then identified with the nucleon and Roper resonance.

hep-ph↗

arXiv2005

Phenomenological study of two-meson couplings of Theta+

We evaluate two-meson couplings of Theta+, using experimental information of nucleon resonances decaying into pi pi N channels, in which the two pions are in scalar- and vector-type correlations. We examine two assignments of spin and parity of J^P=1/2^+ and 3/2^-, for which the experimental spectra of known resonances with exotic baryons are properly reproduced by an octet-antidecuplet representation mixing scheme. With the obtained coupling constants, total cross sections of the reactions pi- p -> K- Theta+ and K+ p -> pi+ Theta+ are calculated. Substantial interference of two terms may occur in the reaction processes for the J^P=1/2^+ case, whereas the interference effect is rather small for the 3/2^- case.

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arXiv2005

Lambda(1520,3/2^-) photoproduction reaction via gamma N -> K Lambda(1520)

We investigate Lambda(1520,3/2^-,D_03) photoproduction via the gamma N -> K Lambda^* reaction process. Using effective Lagrangians, we compute the total and differential cross sections as well as the dependence on the momentum transfer for the photoproduction at the tree-level. We employ two different form factors: The four-dimensional gauge-invariant type and the three dimensional one depending on the external momenta. We find that the total cross sections for the proton target are well reproduced as compared with the experimental data. It turns out that the total cross sections for the neutron target are significantly smaller than those for the proton target. We also compare the present results with the gamma N -> bar{K} Theta^+ reaction in order to extract information of Theta^+. Finally the role of K^*--exchange in the production reaction is discussed.

hep-ph↗

arXiv2005

Path-integral approach in a chiral quark-diquark model to the nucleon structure and interactions

We study the structure of the nuclear force by using a path-integral hadronization approach in a chiral quark-diquark model. After the construction of the chiral quark-diquark model, we hadronize it to obtain a meson-baryon Lagrangian. The effective meson-baryon Lagrangian incorporates chiral symmetry and the composite description of the mesons and baryons. Using the effective meson-baryon Lagrangian we investigate the structure of the nuclear force in the simple case of neglecting the axial-vector diquark. It is shown that the meson-baryon Lagrangian contains two kinds of the nuclear force; the meson-exchange interaction and a quark-diquark loop interaction. It is also shown that the quark-diquark loop interaction consists of the scalar and vector interactions. The properties of these interactions are discussed.

hep-ph↗

arXiv2005

Structure and reactions of pentaquark baryons

We review the current status of the exotic pentaquark baryons. After a brief look at experiments of both positive and negative results, we discuss theoretical methods to study the structure and reactions for the pentaquarks. First we introduce the quark model and the chiral soliton model, where we discuss the relation of mass spectrum and parity with some emphasis on the role of chiral symmetry. It is always useful to picture the structure of the pentaquarks in terms of quarks. As for other methods, we discuss a model independent method, and briefly mention the results from the lattice and QCD sum rule. Decay properties are then studied in some detail, which is one of the important properties of Theta+. We investigate the relation between the decay width and the quark structure having certain spin-parity quantum numbers. Through these analyses, we consider as plausible quantum numbers of Theta+, JP = 3/2-. In the last part of this note, we discuss production reactions of Theta+ which provide links between the theoretical models and experimental information. We discuss photoproductions and hadron-induced reactions which are useful to explore the nature of Theta+

hep-ph↗

arXiv2005

Suppression of Theta^+(J^P=3/2^(+,-)) photoproduction from the proton

We investigate the photoproduction of Theta^+ from the proton and neutron, gamma N -> Kbar Theta^+. Assuming that spin and parity of Theta^+ are J^P = 3/2^(+,-), it is shown that the production from the proton is strongly suppressed as compared with that from the neutron. This could provide a possible explanation for the null results of the recent CLAS experiment in finding Theta^+ via the reaction gamma p -> Kbar^0 Theta^+.

hep-ph↗

arXiv2005

Non-interacting KN contribution in the QCD sum rule for the pentaquark Theta^+(1540)

We perform a QCD sum rule analysis for the pentaquark baryon Theta^+ with the non-interacting $KN$ contribution treated carefully. The coupling of the Theta^+ current to the $KN$ state is evaluated by applying the soft kaon theorem and vacuum saturation. When using a five-quark current including scalar and pseudo-scalar diquarks, the KN contribution turns out not to be very important and the previous result of the negative parity Theta^+ is reproduced again. The Borel analysis of the correlation function for Theta^+ with the KN continuum states subtracted yields the mass of the J^P= 1/2^- Theta^+ around 1.5 GeV.

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