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Kenta Itahashi

Publications and source records attributed to Kenta Itahashi.

12 recordsLinked to original sources
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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arXiv2023

Chiral symmetry restoration at high matter density observed in pionic atoms

Modern theories of physics tell that the vacuum is not an empty space. Hidden in the vacuum is a structure of anti-quarks $\bar{q}$ and quarks $q$. The $\bar{q}$ and $q$ pair has the same quantum number as the vacuum and condensates in it since the strong interaction of the quantum chromodynamics (QCD) is too strong to leave it empty. The $\bar{q}q$ condensation breaks the chiral symmetry of the vacuum. The expectation value $<\bar{q}q>$ is an order parameter. For higher temperature or higher matter-density, $|<\bar{q}q>|$ decreases reflecting the restoration of the symmetry. In contrast to these clear-cut arguments, experimental evidence is so far limited. First of all, the $\bar{q}q$ is nothing but the vacuum itself. It is neither visible nor perceptible. In this article, we unravel this invisible existence by high precision measurement of pionic atoms, $π^-$-meson-nucleus bound systems. Using the $π^-$ as a probe, we demonstrate that $|<\bar{q}q>|$ is reduced in the nucleus at 58% of the normal nuclear density by a factor of 77 $\pm$ 2% compared with that in the vacuum. This reduction indicates that the chiral symmetry is partially restored due to the extremely high density of the nucleus. The present experimental result clearly exhibits the existence of the hidden structure, the chiral condensate, in the vacuum.

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arXiv2023

Pion-nucleon sigma term $σ_{πN}$ and deeply bound pionic atoms

We investigate the possibility to determine the value of the pion-nucleon sigma term $σ_{πN}$ precisely by the experimental observables of the deeply bound pionic atoms. We discuss the sensitivity of the observables to $σ_{πN}$ and take into account the typical errors of the up-to-date experiments of the deeply bound pionic atoms. We find that the gap of the binding energies and the width of the deeply bound pionic states are good observables for the $σ_{πN}$ value determination by the experimental data. We also discuss the expected difficulties for the accurate determination of the value of $σ_{πN}$ due to the correlation between the $σ$ term and the potential parameter in the pion-nucleus optical potential.

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arXiv2021

Structure of double pionic atoms

We study theoretically the structure of double pionic atoms, in which two negatively charged pions ($π^-$) are bound in the atomic orbits. The double pionic atom is considered to be an interesting system from the point of view of the multi bosonic systems. In addition, it could be possible to deduce valuable information on the isospin $I = 2$ $ππ$ interaction and the pion-nucleus strong interaction. In this paper, we take into account the $ππ$ strong and electromagnetic interactions, and evaluate the effects on the binding energies by perturbation theory for the double pionic atoms in heavy nuclei. We investigate several combinations of two pionic states and find that the order of magnitude of the energy shifts due to the $ππ$ interaction is around 10 keV for the strong interaction and around 100 keV for the electromagnetic interaction for the ground states.

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arXiv2017

Search for Tetraneutron by Pion Double Charge Exchange Reaction at J-PARC

Tetraneutron ($^4n$) has come back in the limelight, because of recent observation of a candidate resonant state at RIBF. We propose to investigate the pion double charge exchange (DCX) reaction, i.e. $^4\mathrm{He}(π^- , π^+)$, as an alternative way to populate tetraneutron. An intense $π^-$ beam with the kinetic energy of ~850 MeV, much higher than that in past experiments at LAMPF and TRIUMF, will open up a possibility to improve the experimental sensitivity of the formation cross section, which will be much smaller than hitherto known DCX cross sections such as $^9\mathrm{Be}(π^-, π^+)^9\mathrm{He}\ (g.s.)$.

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arXiv2015

Search for the deeply bound $K^-pp$ state from the semi-inclusive forward-neutron spectrum in the in-flight $K^-$ reaction on helium-3

An experiment to search for the $K^-pp$ bound state was performed via the in-flight $^3$He($K^-,n)$ reaction using 5.3 $\times$ $10^9$ kaons at 1 GeV/$c$ at the J-PARC hadron experimental facility. In the semi-inclusive neutron missing-mass spectrum at $θ_{n}^{lab}=0^\circ$, no significant peak was observed in the region corresponding to $K^-pp$ binding energy larger than 80 MeV, where a bump structure has been reported in the $Λp$ final state in different reactions. Assuming the state to be isotropically decaying into $Λp$, mass-dependent upper limits on the production cross section were determined to be 30--180, 70--250, and 100--270 $μ$b/sr, for the natural widths of 20, 60, and 100 MeV, respectively, at 95\% confidence level.

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arXiv2012

The K1.8BR spectrometer system at J-PARC

A new spectrometer system was designed and constructed at the secondary beam line K1.8BR in the hadron hall of J-PARC to investigate $\bar K N$ interactions and $\bar K$-nuclear bound systems. The spectrometer consists of a high precision beam line spectrometer, a liquid $^3$He/$^4$He/D$_2$ target system, a Cylindrical Detector System that surrounds the target to detect the decay particles from the target region, and a neutron time-of-flight counter array located $\sim$15 m downstream from the target position. Details of the design, construction, and performance of the detector components are described.

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arXiv2012

Spectroscopy of eta' mesic nuclei with (p,d) reaction

We are going to perform an inclusive spectroscopy experiment of eta' mesic nuclei with the 12C(p,d) reaction to study in-medium properties of the eta' meson. In nuclear medium, the eta' meson mass may be reduced due to partial restoration of chiral symmetry. In case of sufficiently large mass reduction and small absorption width of eta' at normal nuclear density, peak structures of eta' mesic states in 11C will be observed near the eta' emission threshold even in an inclusive spectrum. The experiment will be carried out at GSI with proton beam supplied by SIS using FRS as a spectrometer. The detail of the experiment is described.

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arXiv2012

Spectroscopy of eta'-nucleus bound states at GSI-SIS

The eta' meson mass may be reduced due to partial restoration of chiral symmetry. If this is the case, an eta'-nucleus system may form a nuclear bound state. We plan to carry out a missing-mass spectroscopy with the 12C(p,d) reaction at GSI-SIS. Peak structures corresponding to such a bound state may be observed even in an inclusive measurement, if the decay width is narrow enough.

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arXiv2012

Feasibility Study of Observing eta' Mesic Nuclei with (p,d) Reaction

A novel method is proposed to measure eta'(958) meson bound states in 11C nuclei by missing mass spectroscopy of the 12C(p,d) reaction near the eta' production threshold. It is shown that peak structures will be observed experimentally in an inclusive measurement in case that the in-medium eta' mass reduction is sufficiently large and that the decay width of eta' mesic states is narrow enough. Such a measurement will be feasible with the intense proton beam supplied by the SIS synchrotron at GSI combined with the good energy resolution of the fragment separator FRS.

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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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