arXiv subjects

Junko Yamagata-Sekihara

Publications and source records attributed to Junko Yamagata-Sekihara.

13 recordsLinked to original sources

arXiv2026

First Measurement of the $K^-$ Escape Cross Section in the ${}^{12}{\rm C}(K^{-},p)$ Reaction

We investigated the $\bar{K}$-nucleus interaction through the simultaneous measurement of the inclusive $^{12}{\rm C}(K^-, p)$ and exclusive $K^-$-escape $^{12}{\rm C}(K^-, p K^-_{esc})$ reactions at $1.8$ GeV/$c$ at J-PARC. The present measurement explicitly focuses on the $K^-$ escape process for the first time, successfully accomplishing a direct experimental determination of the imaginary part of the $K^-$ optical potential. The differential cross section for the $K^-$-escape reaction was determined to be $436 \pm 6\:(\text{stat.}) \pm 44\:(\text{syst.})~μ\text{b/sr}$. A simultaneous likelihood fit yielded real and imaginary potential strengths of $V_0 = -72\:^{+3}_{-5}\:(\text{stat.})\:^{+0}_{-8}\:(\text{syst.})~\text{MeV}$ and $W_0 = -100\:^{+7}_{-1}\:(\text{stat.})\:^{+0}_{-16}\:(\text{syst.})~\text{MeV}$ at the nuclear center, respectively. The derived $W_0$ is significantly stronger than that predicted by theoretical models based on one-nucleon processes, suggesting possible contribution of multi-nucleon involving processes.

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arXiv2026

Feasibility of the observation of $η^{\prime}$ mesic nuclei in the semi-exclusive $^{12}$C($p, dp$) reaction

We study theoretically the feasibility of the semi-exclusive $^{12}$C($p,dp$)$X$ reaction for the observation of $η^\prime$ mesic nuclei using the microscopic transport model JAM. The semi-exclusive measurements of the ($p,d$) reaction with protons from $η^\prime$ absorption are found to be significant for the observation of the $η^\prime$ bound states. Especially, the measurements of the energetic protons from $η^\prime$ non-mesic two-body absorption ($η^\prime NN \to NN$) are considered to be critically important. The Green's function method is used to calculate the expected spectrum of forward going deuterons corresponding to the excitation energy spectrum of the $η^\prime \otimes {}^{11}$C system in the semi-exclusive measurement. The semi-exclusive measurements are shown to be important in general for the $η^\prime$ mesic nucleus observation.

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arXiv2026

Structure and Formation of the Deeply Bound $\bar{p}$ atoms

We study theoretically the structure and formation of the deeply bound $\bar{p}$ atoms. We find that the widths of the atomic states are narrower than the level spacing even for deeply bound states so that the well-isolated deeply bound $\bar{p}$ atoms are expected to exist. We also find the $\bar{p}$-nuclear states with huge widths. For the observation of the deep $ {\bar p}$-atomic states, we investigate theoretically the $(\bar{p}, p)$ reactions for $^{12}$C, $^{16}$O, and $^{31}$P target nuclei. We find that the momentum transfer of the $( {\bar p},p)$ reaction is small and the formation of the $ {\bar p}$-atomic states can be observed as the discrete peak structures in the $( {\bar p},p)$ spectrum. We conclude that the $(\bar{p}, p)$ reactions are very much suited for the $\bar{p}$ atom formation and the spectra of the reaction are expected to provide new valuable information on the $ {\bar p}$ atoms and $ {\bar p}$-nucleus interaction.

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arXiv2025

Interrelation between $\bar{p}$-Ca Atom Spectra and Nuclear Density Profiles

This work studies $\bar{p}$-Ca atom spectra in light of the strong shifts and level widths, using the optical model with several types of parametric coefficients. The spectroscopic quantities are obtained as the eigenvalues of the Dirac equation, where the nuclear densities computed via nuclear Density Functional Theory and the effect of the anomalous magnetic moment are incorporated. The results indicate that the isovector term's contribution to the optical potential is crucial for explaining the systematical differences in the strong shifts between $^{40}$Ca and $^{48}$Ca. Furthermore, it is found that both the strong shifts and the level widths exhibit significant dependence on the nuclear density profiles. These findings provide critical insights into the nuclear structures, particularly in the context of Calcium isotopes, by offering a more comprehensive understanding of the underlying nuclear-hadron properties.

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arXiv2019

Origin of energy shift in kaonic atom and kaon-nucleus interaction

The $K^-$-nucleus optical potential is revisited to investigate its global feature phenomenologically. It is a puzzle that the energy shift is found to be repulsive in all of the observed kaonic atom, although the $K^-N$ interaction is known to be so attractive as to form the $Λ(1405)$ resonance. To solve this puzzle, we examine the $K^-$ optical potential in the linear density approximation and determine the potential parameters of each kaonic atom so as to reproduce the observed energy shift and absorption width. We find two types of the potentials. One potential has a so large real part as to provide nuclear states with the same quantum number to the atomic state in the last orbit. The level repulsion between the atomic state and the nuclear states takes place due to their mixing, and it makes the atomic state shifted repulsively. The other type of the potential has a large imaginary part and the imaginary part works repulsively for atomic states. We find that only the latter solution reproduce a wide of the observed data, and thus is realized as a $K^-$-nucleus potential for kaonic atom. In the linear nuclear density optical potential, the picture that the repulsive shifts in the atomic states stem from the existence of the nuclear states does not globally stand up. This implies that the $K^-$-nucleus optical potential should have a large imaginary part. We examine some nonlinear density effects and find that the conclusion does not change. We also confirm that the conventionally known optical potentials are categorized into the latter type of the potential.

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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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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.

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arXiv2016

Compositeness of baryonic resonances: Applications to the Delta(1232), N(1535), and N(1650) resonances

We present a formulation of the compositeness for baryonic resonances in order to discuss the meson-baryon molecular structure inside the resonances. For this purpose, we derive a relation between the residue of the scattering amplitude at the resonance pole position and the two-body wave function of the resonance in a sophisticated way, and we define the compositeness as the norm of the two-body wave functions. As applications, we investigate the compositeness of the $Δ(1232)$, $N (1535)$, and $N (1650)$ resonances from precise $πN$ scattering amplitudes in a unitarized chiral framework with the interaction up to the next-to-leading order in chiral perturbation theory. The $πN$ compositeness for the $Δ(1232)$ resonance is evaluated in the $πN$ single-channel scattering, and we find that the $πN$ component inside $Δ(1232)$ in the present framework is nonnegligible, which supports the previous work. On the other hand, the compositeness for the $N (1535)$ and $N (1650)$ resonances is evaluated in a coupled-channels approach, resulting that the $πN$, $ηN$, $K Λ$ and $K Σ$ components are negligible for these resonances.

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arXiv2015

Compositeness of the Delta(1232) resonance in pi N scattering

We evaluate the $πN$ compositeness of the $Δ(1232)$ resonance so as to clarify the internal structure of $Δ(1232)$ in terms of the $πN$ component. Here the compositeness is defined as contributions from two-body wave functions to the normalization of the total wave function and is extracted from the $πN$ scattering amplitude. In this study we employ the chiral unitary approach with the interaction up to the next-to-leading order plus a bare $Δ$ term in chiral perturbation theory and describe $Δ(1232)$ in an elastic $πN$ scattering. Fitting the $πN$ scattering amplitude to the solution of the partial wave analysis, we obtain a large real part of the $πN$ compositeness for $Δ(1232)$ comparable to unity and non-negligible imaginary part as well, with which we reconfirm the result in the previous study on the $πN$ compositeness for $Δ(1232)$.

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arXiv2013

(d,3He) reaction on odd-neutron nuclear target for the formation of deeply bound pionic atoms

We consider the pionic atom spectroscopy by the (d,3He) reaction on an odd-neutron nuclear target in this article, which has not been investigated so far. In the (d,3He) reaction on the odd-neutron nuclear target, we can observe the pionic states in the even-neutron nucleus with spin-parity 0+. We expect that this pionic state does not have the additional shifts due to the effects of the residual interaction between neutron-hole and pionic states. For the even-neutron nuclear target cases, we may have to take into account the residual interaction effects to deduce the binding energies of the pionic states precisely from the high precision experimental data since the final pionic states are the pion-particle plus neutron-hole states. Thus, in addition to widening the domain of the pionic atom spectroscopy in nuclear chart, the present study of the (d,3He) reaction on the odd-neutron target is considered to be important to deduce extremely precise information on the binding energies of the observed pionic states, and to know the pion properties and aspects of the symmetries of the strong interaction at finite density. We modify the formula of the even-even nuclear target case to study the pionic atom formation spectra on the even-odd nuclear target and show the numerical results of 117Sn target case. This experiment will be performed at RIBF/RIKEN in near future.

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arXiv2013

Mesonic and non-mesonic branching ratios of K^- absorption in the nuclear medium

The branching ratios of K^- absorption at rest in nuclear matter are evaluated from the K^- self-energy by using the chiral unitary approach for the s-wave \bar{K} N amplitude. We find that both the mesonic and non-mesonic absorption potentials are dominated by the Λ(1405) contributions. We also observe that the mesonic absorption ratio [π^{-} Σ^{+}] / [π^{+} Σ^{-}] increases as a function of nuclear density due to the interference between Λ(1405) and the I=1 non-resonant background, which is consistent with experimental results. The fraction of the non-mesonic absorption is evaluated to be about 30 % at the saturation density. The branching ratios of the K^- absorption at rest into deuteron and 4He are also calculated.

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arXiv2012

Branching ratios of mesonic and nonmesonic antikaon absorptions in nuclear medium

The branching ratios of K^- absorption at rest in nuclear matter are theoretically investigated in order to understand the mechanism of K^- absorption into nuclei. For this purpose mesonic and nonmesonic absorption potentials are evaluated as functions of nuclear density, the kaon momentum and energy from one- and two-body K^- self-energy, respectively. By using a chiral unitary approach for the s-wave Kbar N amplitude we find that both the mesonic and nonmesonic absorption potentials are dominated by the Lambda(1405) contributions. The fraction of the mesonic and nonmesonic absorptions are evaluated to be respectively about 70% and 30% at the saturation density almost independently on the kaon momentum. We also observe different behavior of the branching ratios to pi ^+ Sigma^- and pi^- Sigma^+ channels in mesonic absorption due to the interference between Lambda(1405) and the I=1 nonresonant background, which is consistent with experimental results. The nonmesonic absorption ratios [Lambda p]/[Sigma^0 p] and [Lambda n]/[Sigma^0 n] are about unity while [Sigma^+ n]/[Sigma^0 p] and [Sigma^- p]/[Sigma^0 n] are about two due to the Lambda(1405) dominance in absorption. Taking into account the kaon momenta and energies, the absorption potentials become weaker due to the downward shift of the initial K^-N two-body energy, but this does not drastirally change the nonmesonic fraction. The Sigma(1385) contribution in the p-wave Kbar N amplitude is examined and found to be very small compared to the Lambda(1405) contribution in slow K^- absorption.

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arXiv2011

Precision Spectroscopy of Deeply Bound Pionic Atoms and Partial Restoration of Chiral Symmetry in Medium

We study theoretically the formation spectra of deeply bound pionic atoms expected to be observed by experiments with high energy resolution at RIBF/RIKEN, and we discuss in detail the possibilities to extract new information on the pion properties at finite density from the observed spectra, which may provide information on partial restoration of chiral symmetry in medium. We find that the non-yrast pionic states such as 2s are expected to be seen in the (d,3He) spectra, which will be helpful to reduce uncertainties of the theoretical calculations in the neutron wave functions in nucleus. The observation of the 2s state with the ground 1s state is also helpful to reduce the experimental uncertainties associated in the calibration of the absolute excitation energy. We find that the nuclear densities probed by atomic pions are quite stable and almost constant for various atomic states and various nuclei. Effects of the pion wave function renormalization to the formation spectra are also evaluated.

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