arXiv subjects

Takayasu Sekihara

Publications and source records attributed to Takayasu Sekihara.

At least 19 recordsLinked to original sources

arXiv2026

Model analysis on the effectiveness of the HAL QCD method for hadron-hadron interactions

The HAL QCD method has been one of the powerful tools to extract hadron-hadron interactions directly from lattice QCD simulation data. In this paper, we aim at examining the effectiveness of the HAL QCD method by deriving a formula to calculate quantities in the HAL QCD method, such as the so-called R-correlators and HAL QCD local potentials, from the hadron-hadron scattering amplitudes within effective models. In this framework, we can judge whether the HAL QCD local potential, evaluated in the present formula, reproduces the properties of the original hadron-hadron interaction or not via the scattering amplitude, which is a solution of the Lippmann--Schwinger equation with the original hadron-hadron interaction as an input. In an analysis within a simple model of elastic scattering, we show that, when the original interaction is predominantly local, the HAL QCD local potentials quantitatively reproduce phase shifts of the hadron-hadron scatterings and correctly indicate the existence/absence of the bound state with its binding energy $\sim$ MeV. Lattice discretization of spacetime modifies the results only slightly. Furthermore, we consider the $\bar{K} N$ potential in a bare to $\bar{K} N$ transition amplitude, which shows singular behavior around the origin in the recent HAL QCD results of the lattice QCD simulation data, and discuss the cause of such singular behavior in the HAL QCD method through our model analysis of the $\bar{K} N$ scattering.

hep-ph↗

arXiv2023

Short-range baryon-baryon potentials in constituent quark model revisited

We revisit the short-range baryon-baryon potentials in the flavor SU(3) sector, using the constituent quark model. We employ the color Coulomb, linear confining, and color magnetic forces between two constituent quarks, and solve the three-quark Schrödinger equation using the Gaussian expansion method to evaluate the wave functions of the octet $( N , Λ, Σ, Ξ)$ and decuplet $( Δ, Σ^{\ast} , Ξ^{\ast} , Ω)$ baryons. We then solve the six-quark equation using the resonating group method and systematically calculate equivalent local potentials for the $S$-wave two-baryon systems which reproduce the relative wave functions of two baryons in the resonating group method. As a result, we find that the flavor antidecuplet states with total spin $J = 3$, namely, $ΔΔ$, $ΔΣ^{\ast}$, $ΔΞ^{\ast}$-$Σ^{\ast} Σ^{\ast}$, and $ΔΩ$-$Σ^{\ast} Ξ^{\ast}$ systems, have attractive potentials sufficient to generate dibaryon bound states as hadronic molecules. In addition, the $N Ω$ system with $J = 2$ in coupled channels has a strong attraction and forms a bound state. We also make a comparison with the baryon-baryon potentials from lattice QCD simulations and try to understand the behavior of the potentials from lattice QCD simulations.

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arXiv2021

Extension of the J-PARC Hadron Experimental Facility: Third White Paper

The J-PARC Hadron Experimental Facility was constructed with an aim to explore the origin and evolution of matter in the universe through the experiments with intense particle beams. In the past decade, many results on particle and nuclear physics have been obtained at the present facility. To expand the physics programs to unexplored regions never achieved, the extension project of the Hadron Experimental Facility has been extensively discussed. This white paper presents the physics of the extension of the Hadron Experimental Facility for resolving the issues in the fields of the strangeness nuclear physics, hadron physics, and flavor physics.

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arXiv2021

Two-body wave functions and compositeness from scattering amplitudes: II. Application to the physical $N ^{\ast}$ and $Δ^{\ast}$ resonances

The meson-baryon molecular components for the $N^{\ast}$ and $Δ^{\ast}$ resonances are investigated in terms of the compositeness, which is defined as the norm of the two-body wave function from the meson-baryon scattering amplitudes. The scattering amplitudes are constructed in a $πN$-$ηN$-$σN$-$ρN$-$πΔ$ coupled-channels problem in a meson exchange model together with several bare $N^{\ast}$ and $Δ^{\ast}$ states, and parameters are fitted so as to reproduce the on-shell $πN$ partial wave amplitudes up to the center-of-mass energy 1.9 GeV with the orbital angular momentum $L \le 2$. As a result, the Roper resonance $N (1440)$ is found to be dominated by the $πN$ and $σN$ molecular components while the bare-state contribution is small. The squared wave functions in coordinate space imply that both in the $πN$ and $σN$ channels the separation between the meson and baryon is about more than 1 fm for the $N (1440)$ resonance. On the other hand, dominant meson-baryon molecular components are not observed in any other $N^{\ast}$ and $Δ^{\ast}$ resonances in the present model, although they have some fractions of the meson-baryon clouds.

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arXiv2020

Feasibility study of the $K^{+} d \to K^{0} p p$ reaction for the "$Θ^{+}$" pentaquark

We investigate theoretically the $K^{0} p$ invariant mass spectrum of the $K^{+} d \to K^{0} p p$ reaction and scrutinize how the signal of the "$Θ^{+}$" pentaquark, if it exists, emerges in the $K^{0} p$ spectrum. The most prominent advantage of this reaction is that we can clearly judge whether the "$Θ^{+}$" exists or not as a direct-formation production without significant backgrounds, in contrast to other reactions such as photoproduction and $π$-induced productions. We show that while the impulse or single-step scattering process can cover the "$Θ^{+}$" energy region with an initial kaon momentum $k_{\mathrm{lab}} \approx 0.40\, \mathrm{GeV} / c$ in the laboratory frame, the contributions from double-step processes may have a potential possibility to reach the "$Θ^{+}$" energy region with a higher kaon momentum $k_{\mathrm{lab}} \sim 1 \, \mathrm{GeV} / c$. Assuming that the full decay width of the "$Θ^{+}$" is around $0.5\, \mathrm{MeV}$, we predict that the magnitude of the peak corresponding to the "$Θ^+$" is around a few hundred $μ\mathrm{b}$ to $1\, \mathrm{mb}$ with the momentum of the kaon beam $k_{\mathrm{lab}} \approx 0.40\, \mathrm{GeV} / c$ while it is around $\lesssim 1\, μ\mathrm{b}$ with $k_{\mathrm{lab}} \approx 0.85\, \mathrm{GeV} / c$. Thus, the "$Θ^+$" peak is more likely to be seen at $k_{\mathrm{lab}} \approx 0.40\, \mathrm{GeV} / c$ than at $k_{\mathrm{lab}} \approx 0.85 \,\mathrm{GeV} / c$.

hep-ph↗

arXiv2019

Further Theoretical Analysis on the $K^{-} {}^{3} \text{He} \to Λp n$ Reaction for the $\bar{K} N N$ Bound-State Search in the J-PARC E15 Experiment

Based on the scenario that a $\bar{K} N N$ bound state is generated and it eventually decays into $Λp$, we calculate the cross section of the $K^{-} {}^{3} \text{He} \to Λp n$ reaction, which was recently measured in the J-PARC E15 experiment. We find that the behavior of the calculated differential cross section $d ^{2} σ/ d M_{Λp} d q_{Λp}$, where $M_{Λp}$ and $q_{Λp}$ are the $Λp$ invariant mass and momentum transfer in the $(K^{-} , \, n)$ reaction in the laboratory frame, respectively, is consistent with the experiment. Furthermore, we can reproduce almost quantitatively the experimental data of the $Λp$ invariant mass spectrum in the momentum transfer window $350 \text{ MeV} /c < q_{Λp} < 650 \text{ MeV} /c$. These facts strongly suggest that the $\bar{K} N N$ bound state was indeed generated in the J-PARC E15 experiment.

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arXiv2018

$\bar{K}\bar{D} N$ molecular state as a "$u u d s \bar{c}$ pentaquark" in a three-body calculation

We predict a new three-body hadronic molecule composed of antikaon $\bar{K}$, anticharm meson $\bar{D}$, and nucleon $N$ with spin/parity $J^{P} = 1/2^{+}$ and isospin $I = 1/2$. This state behaves like an explicit pentaquark state because its minimal quark configuration is $u u d s \bar{c}$ or $u d d s \bar{c}$. Owing to the attraction between every pair of two hadrons, in particular the $\bar{K}\bar{D}$ attraction which dynamically generates $D_{s 0} (2317)^{-}$ and $\bar{K} N$ attraction which dynamically generates $Λ(1405)$, the $\bar{K}\bar{D} N$ system is bound, and its eigenenergy is calculated as $3244 - 17 i$ MeV in a nonrelativistic three-body potential model. We discuss properties of this $\bar{K} \bar{D} N$ quasibound state which emerge uniquely in three-body dynamics.

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arXiv2018

$N Ω$ interaction: meson exchanges, inelastic channels, and quasibound state

Based on a baryon-baryon interaction model with meson exchanges, we investigate the origin of the strong attraction in the $N Ω( {}^{5}S_{2} )$ interaction, which was indicated by recent lattice QCD simulations. The long range part of the potential is constructed by the conventional mechanisms, the exchanges of the $η$ meson and of the correlated two mesons in the scalar-isoscalar channel, denoted by "$σ$" in the literature. The short range part is represented by the contact interaction. We find that the meson exchanges do not provide sufficient attraction. This means that most of the attraction is attributed to the short range contact interaction. We then evaluate the effect of the coupled channels to the $N Ω( {}^{5}S_{2} )$ interaction. We find that, while the $D$-wave mixing of the $N Ω$ channel is negligible, the inelastic $ΛΞ$, $ΣΞ$, and $ΛΞ(1530)$ channels via the $K$ meson exchange give the attraction of the $N Ω( {}^{5}S_{2} )$ interaction to the same level with the elastic meson exchanges. Although the elimination of these channels induces the energy dependence of the single-channel $N Ω$ interaction, this effect is not significant. With the present model parameters fitted to reproduce the scattering length of the HAL QCD result of the nearly physical quark masses, we obtain the $N Ω( {}^{5}S_{2} )$ quasibound state with its eigenenergy $2611.3 - 0.7 i$ MeV, which corresponds to the binding energy $0.1$ MeV and width $1.5$ MeV for the decay to the $ΛΞ$ and $ΣΞ$ channels. From the analysis of the spatial structure and the compositeness, the quasibound state is shown to be the molecular state of $NΩ$. We also construct an equivalent local potential for the $N Ω( {}^{5}S_{2} )$ system which is useful for various applications.

hep-ph↗

arXiv2018

Possible $η' d$ bound state and its $s$-channel formation in the $γd \to ηd$ reaction

We theoretically investigate a possibility of an $η^{\prime} d$ bound state and its formation in the $γd \to ηd$ reaction. First, in the fixed center approximation to the Faddeev equations we obtain an $η^{\prime} d$ bound state with a binding energy of 25 MeV and width of 19 MeV, where we take the $η^{\prime} N$ interaction with a coupling to the $ηN$ channel from the linear $σ$ model. Then, in order to investigate the feasibility from an experimental point of view, we calculate the cross section of the $γd \to ηd$ reaction at the photon energy in the laboratory frame around 1.2 GeV. As a result, we find a clear peak structure with the strength $\sim$ 0.2 nb/sr, corresponding to a signal of the $η^{\prime} d$ bound state in case of backward $η$ emission. This structure will be prominent because a background contribution coming from single-step $η$ emission off a bound nucleon is highly suppressed. In addition, the signal can be seen even in case of forward $η$ emission as a bump or dip, depending on the relative phase between the bound-state formation and the single-step background.

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arXiv2018

Theoretical analysis on the $K^{-} {}^{3} \text{He} \to Λp n$ reaction for the $\bar{K} N N$ bound-state search in the J-PARC E15 experiment

We theoretically analyze the $K^{-} {}^{3} \text{He} \to Λp n$ reaction for the $\bar{K} N N$ bound-state search in the J-PARC E15 experiment. We find that, by detecting a fast and forward neutron in the final state, an almost on-shell $\bar{K}$ is guaranteed, which is essential to make a bound state with two nucleons from ${}^{3} \text{He}$. Then, this almost on-shell $\bar{K}$ can bring a signal of the $\bar{K} N N$ bound state in the $Λp$ invariant-mass spectrum, although it inevitably brings a kinematic peak above the $\bar{K} N N$ threshold as well. As a consequence, we predict two peaks across the $\bar{K} N N$ threshold in the spectrum: the lower peak coming from the $\bar{K} N N$ bound state, and the higher one originating from the kinematics.

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arXiv2017

What makes the peak structure of the $Λp$ invariant-mass spectrum in the $K^{-} {}^{3} {\rm He} \to Λp n$ reaction?

Recently a peak structure was observed near the $K^{-} p p$ threshold in the in-flight ${}^{3} {\rm He} (K^{-} , \, Λp) n$ reaction of the E15 experiment at J-PARC, which could be a signal of a $\bar{K} N N$ bound state. In order to investigate what is the origin of this peak, we calculate the cross section of this reaction, in particular based on the scenario that the $\bar{K} N N$ bound state is indeed generated and decays into $Λp$. We find that the numerical result of the $Λp$ invariant-mass spectrum in the $\bar{K} N N$ bound scenario is consistent with the J-PARC E15 data.

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arXiv2017

Two-body Wave Functions, Compositeness, And The Internal Structure Of Dynamically Generated Resonances

Recently, the compositeness, defined as the norm of a two-body wave function for bound and resonance states, has been investigated to discuss the internal structure of hadrons in terms of hadronic molecular components. From the studies of the compositeness, it has been clarified that the two-body wave function of a bound state can be extracted from the residue of the scattering amplitude at the bound state pole. Of special interest is that the two-body wave function from the scattering amplitude is automatically normalized. In particular, while the compositeness is unity for energy-independent interactions, it deviates from unity for energy-dependent interactions, which can be interpreted as a missing-channel contribution. In this manuscript, we show the formulation of the two-body wave function from the scattering amplitude, evaluate the compositeness for several dynamically generated resonances such as $f_{0} (980)$, $Λ(1405)$, and $Ξ(1690)$, and investigate their internal structure in terms of the hadronic molecular components.

hep-ph↗

arXiv2017

Two-body wave functions and compositeness from scattering amplitudes. I. General properties with schematic models

For a general two-body bound state in quantum mechanics, both in the stable and decaying cases, we establish a way to extract its two-body wave function in momentum space from the scattering amplitude of the constituent two particles. For this purpose, we first show that the two-body wave function of the bound state corresponds to the residue of the off-shell scattering amplitude at the bound state pole. Then, we examine our scheme to extract the two-body wave function from the scattering amplitude in several schematic models. As a result, the two-body wave functions from the Lippmann--Schwinger equation coincides with that from the Schrödinger equation for an energy-independent interaction. Of special interest is that the two-body wave function from the scattering amplitude is automatically scaled; the norm of the two-body wave function, to which we refer as the compositeness, is unity for an energy-independent interaction, while the compositeness deviates from unity for an energy-dependent interaction, which can be interpreted to implement missing channel contributions. We also discuss general properties of the two-body wave function and compositeness for bound states in the schematic models.

quant-ph↗

arXiv2017

Exotic Hadrons from Heavy Ion Collisions

Heavy ion collisions (HIC) at high energies are excellent ways for producing heavy hadrons and composite particles. With upgraded detectors at RHIC and LHC, it has become possible to measure hadrons beyond their ground states. Therefore, HIC provide a new method for studying exotic hadrons that are either hadronic molecular states or compact multiquark systems. Because their structures are related to the fundamental properties of QCD, studying exotic hadrons is currently one of the most active areas of research in hadron physics. Experiments carried out at various accelerator facilities have indicated that some exotic hadrons may have already been produced. The present review is a summary of the current understanding of a selected set of exotic particle candidates that can be potentially measured in HIC. It also includes discussions on the production of exotic hadrons in HIC based on the coalescence and statistical models. A more detailed discussion leads to the conclusion that the yield of a hadron is typically an order of magnitude smaller when it is a compact multiquark state than that of an excited hadronic state with normal quark numbers and/or a molecular configuration. Attention is also given to some of the proposed heavy exotic hadrons that could be produced with sufficient abundance in HIC because of the significant numbers of charm and bottom quarks produced at RHIC and LHC, making it possible to study them in these experiments. Further included in the discussion are the general formalism for the coalescence model that involves resonance particles and its implication on the present estimated yield for resonance production. Finally, a review is given on recent studies to constrain the hadron-hadron interaction through correlation measurements in HIC and their implications on the interpretation and the possible existence of exotic states in hadronic interactions.

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arXiv2016

The Peak Structure in the In-Flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ Reaction Around the $\bar{K} N N$ Threshold

We theoretically investigate the origin of the peak structure around the $K^{-} p p$ threshold observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ reaction in the recent E15 experiment at J-PARC. For this purpose, we consider two scenarios to produce the peak. One is that the $Λ(1405)$ is generated but it does not correlate with $p$, and the uncorrelated $Λ(1405) p$ system subsequently decays into $Λp$. The other one is that the $\bar{K} N N$ bound state is indeed generated and decays into $Λp$. As a result, the experimental signal is qualitatively well reproduced in the $\bar{K} N N$ bound scenario, definitely discarding the uncorrelated $Λ(1405) p$ one.

nucl-th↗

arXiv2016

On the structure observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ reaction at J-PARC

A theoretical investigation is done to clarify the origin of the peak structure observed near the $K^{-} p p$ threshold in the in-flight ${}^{3}\text{He} ( K^{-}, \, Λp ) n$ reaction of the J-PARC E15 experiment, which could be a signal of the lightest kaonic nuclei, that is, the $\bar{K} N N (I=1/2)$ state. For the investigation, we evaluate the $Λp$ invariant mass spectrum assuming two possible scenarios to interpret the experimental peak. One assumes that the $Λ(1405)$ resonance is generated after the emission of an energetic neutron from the absorption of the initial $K^-$, not forming a bound state with the remaining proton. This uncorrelated $Λ(1405) p$ system subsequently decays into the final $Λp$. The other scenario implies that, after the emission of the energetic neutron, a $\bar{K} N N$ bound state is formed, decaying eventually into a $Λp$ pair. Our results show that the experimental signal observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ reaction at J-PARC is qualitatively well reproduced by the assumption that a $\bar{K} N N$ bound state is generated in the reaction, definitely discarding the interpretation in terms of an uncorrelated $Λ(1405) p$ state.

hep-ph↗

arXiv2016

Theoretical study of photoproduction of $η^{\prime} N$ bound state on deuteron target with forward proton emission

Possibilities of observing a signal of an $η^{\prime} n$ bound state are investigated by considering photoproductions of the $η$ and $η^{\prime}$ mesons on a deuteron target with forward proton emission. For this purpose, we take the $η^{\prime} n$ interaction from the linear sigma model with a coupling to $ηn$, in which an $s$-wave $η^{\prime} n$ bound state can be dynamically generated, and we fix the $γp \to ηp$ and $η^{\prime} p$ scattering amplitudes so as to reproduce the experimental cross sections with forward proton emission. By using these $γp \to η^{( \prime )} p$ and $η^{( \prime )} n \to η^{( \prime )} n$ amplitudes, we calculate cross sections of the $γd \to ηn p$ and $η^{\prime} n p$ reactions with forward proton emission in single and $η^{(\prime )}$-exchange double scattering processes. As a result, we find that the signal of the $η^{\prime} n$ bound state can be seen below the $η^{\prime} n$ threshold in the $ηn$ invariant mass spectrum of the $γd \to ηn p$ reaction and is comparable with the contribution from the quasifree $η^{\prime}$ production above the $η^{\prime} n$ threshold. We also discuss the behavior of the signal of the $η^{\prime} n$ bound state in several experimental conditions and model parameters.

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arXiv2016

Dynamically Generated $Ξ(1690)$

We show that the $Ξ(1690)$ resonance can be dynamically generated in the $s$-wave $\bar{K} Σ$-$\bar{K} Λ$-$πΞ$-$ηΞ$ coupled-channels chiral unitary approach. In our model, the $Ξ(1690)$ resonance appears near the $\bar{K} Σ$ threshold as a $\bar{K} Σ$ molecular state and the experimental data are reproduced well. We discuss properties of the dynamically generated $Ξ(1690)$.

hep-ph↗