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Hiroyuki Fujioka

Publications and source records attributed to Hiroyuki Fujioka.

At least 19 recordsLinked to original sources
arXiv2026

Toward testing antinucleon$\unicode{x2013}$nucleus optical potentials with antineutron scattering lengths

The antineutron$\unicode{x2013}$nucleus scattering length is currently known only indirectly, via antiproton$\unicode{x2013}$nucleus optical potentials fitted to level shifts and widths of antiprotonic atoms. The antineutron$\unicode{x2013}$nucleus and antiproton$\unicode{x2013}$nucleus potentials are related to each other through charge symmetry. We calculate the scattering length from optical potentials proposed for antiprotonic atoms using nucleon density distributions as input. We find that the scattering length for an $N>Z$ nuclide is largely affected by the poorly constrained neutron density distribution and by a possible isovector interaction, one of the mechanisms introduced to reproduce the isotope dependence of antiprotonic $^{40,48}\mathrm{Ca}$ data. For $^{48}\mathrm{Ca}$, the isovector term modifies the scattering length by $0.3\unicode{x2013}0.4\,\mathrm{fm}$ ($0.4\unicode{x2013}0.5\,\mathrm{fm}$) for the real (imaginary) part, an order of magnitude beyond the uncertainty propagated from the isoscalar potential. As no antineutron$\unicode{x2013}$nucleus scattering data are available below $76\,\mathrm{MeV}/c$, a direct measurement with recently proposed low-energy antineutron beams would provide the first access to the antinucleon$\unicode{x2013}$nucleus interaction in the $s$-wave regime.

nucl-th↗
arXiv2026

Calculation of tetraneutron-induced reaction cross sections with optical and Hauser-Feshbach statistical models

Interactions of tetraneutrons, which are assumed to be produced in the nuclear fission process, with nuclei are studied in the framework of optical and Hauser-Feshbach statistical models. It predicts a large probability of $^{89}\mathrm{Sr}$ production for the tetraneutron-induced reaction on $^{88}\mathrm{Sr}$ compared to other isotopes. The same technique is applied to the tetraneutron-induced reaction on $^{27}\mathrm{Al}$ and the hexaneutron-induced reaction on natural zinc to revisit two historical multi-neutron experiments performed in the past.

nucl-th↗
arXiv2025

Isotone Chain Study of $\bar{p}$-atom spectroscopy and Strong Spin-orbit splittings

Antiprotonic atoms have served as a pivotal tool for investigating the properties of baryon-baryon interactions, including their spin dependence. Examining the spin-orbit splittings induced by their strong interactions also could help clarify the nature of the $\bar{p}$-nucleus interactions and their fraction mediated by scalar and vector mesons. Although the strong spin-orbit splittings for a certain nucleus have been observed experimentally, thorough theoretical investigations have not yet been conducted. In this study, theoretical calculations based on the Dirac equation are systematically performed for nuclei along several isotone ``chains''. As a result, it is found that the magnitude of the strong spin-orbit splittings exhibits a significant dependence not only on the corresponding level shifts and widths almost linearly, but also on whether the optical potential enters as a vector or scalar potential. A simple perturbative analysis indicates that the relativistic corrections have a dominant effect the magnitude of the splittings. These results are expected to provide deeper insights into $\bar{p}$-nucleus interactions, and by extension baryon-baryon interactions, as well as into the properties of the mesons that mediate them.

hep-ph↗
arXiv2025

First Constraint on P-odd/T-odd Cross Section in Polarized Neutron Transmission through Transversely Polarized $^{139}$La

We report the first constraint on time-reversal invariance violating (TRIV) effects in polarized neutron transmission through a transversely polarized $^{139}$La target. We formulate the transmission asymmetry within the density matrix formalism, explicitly incorporating the forward scattering amplitude of $^{139}$La including tensor polarization terms up to third-rank. The formalism is applied to existing transmission data originally obtained to measure the spin-dependent cross section near the $0.75$~eV $p$-wave resonance. Since these data were not optimized for P-odd/T-odd observables, the attainable sensitivity is intrinsically limited; nevertheless, they provide a useful test of the formalism on real experimental data. No statistically significant TRIV signal is observed. By analyzing the global $\chi^2$ structure in the parameter space, we obtain an upper limit of $|W_T|<15~\mathrm{eV}$ at the 90\% confidence level. This corresponds to an upper limit on the resonance-averaged TRIV cross section of $|\Delta\sigma_{\not{T}\not{P}}|<8.3\times10^2~\mathrm{b}$. These results validate the present theoretical framework and provide guidance for future dedicated TRIV searches in polarized neutron transmission experiments.

nucl-ex↗
arXiv2025

Impact of a Reflecting Material on a Search for Neutron--Antineutron Oscillations using Ultracold Neutrons

We investigate neutron--antineutron oscillations of ultracold neutrons in a storage bottle represented by a one-dimensional potential. The experimental sensitivity is determined by the annihilation rate of antineutrons. Its dependence on the antineutron reflectivity and the relative phase shift between the neutron and the antineutron wavefunctions by a reflection from the wall is derived. Optimization of the antineutron pseudopotential was found crucial to maximize the sensitivity of the experiment. Furthermore, methods are discussed for determining the antineutron pseudopotential, which has only been studied indirectly thus far.

hep-ex↗
arXiv2025

Precision Spectroscopy of Antiprotonic Atoms for Investigation of Low-energy Antinucleon-nucleus Interactions

We propose a high-precision x-ray spectroscopy experiment of antiprotonic atoms to advance the understanding of low-energy antinucleon-nucleus interactions. The current leading model of antiproton-nucleus interactions is based on an optical potential with parameters derived from a global fit to antiprotonic atom x-ray data across the periodic table. However, the isovector parameter of this potential remains poorly constrained due to uncertainties in nucleon distributions of the nuclei. To address this, we propose to use calcium isotopes with well-studied nucleon distributions to minimize these uncertainties. A superconducting microcalorimeter detector will provide a resolution of 50-70 eV in the energy range of interest, allowing high precision determination of the isotope-dependent strong-interaction shifts and widths. The outcomes of the proposed experiment can be used to refine the model of antinucleon-nucleus interactions and provide critical data for future experiments searching for neutron-antineutron oscillations.

nucl-ex↗
arXiv2025

Novel concept for low-energy antineutron production and its application for antineutron scattering experiments

Extensive data of antiproton scattering cross sections with protons and nuclei have advanced our understanding of hadronic interactions with antinucleons. However, low-energy antineutron scattering data are scarce, thereby limiting our understanding of the S-wave antinucleon-nucleon and antinucleon-nucleus interactions. We present a novel production scheme of extremely low-energy antineutrons that could remedy this situation. This method is based on backward charge-exchange reaction ($p\bar{p}\to n\bar{n}$), and can reach the lowest momentum of 9 MeV/c, which would be well suited to study of the S-wave antinucleon-nucleon or antinucleon-nucleus interactions.

nucl-ex↗
arXiv2025

Towards Precision Spectroscopy of Antiprotonic Atoms for Probing Strong-field QED

PAX (antiProtonic Atom X-ray spectroscopy) is a new experiment with the aim to test strong-field quantum electrodynamics (QED) effects by performing high-precision x-ray spectroscopy of antiprotonic atoms. By utilizing advanced microcalorimeter detection techniques and a low-energy antiproton beam provided by the ELENA ring at CERN, gaseous targets will be used for the creation of antiprotonic atoms, and the measurement of transitions between circular Rydberg states will be conducted with up to two orders of magnitude improved accuracy over previous studies using high-purity germanium detectors. Our approach eliminates the longstanding issue of nuclear uncertainties that have hindered prior studies using highly charged ions, thus enabling direct and purely QED-focused measurements. By precisely probing atomic systems with electric fields up to two orders of magnitude above the Schwinger limit, PAX will test vacuum polarization and second-order QED corrections, opening new frontiers in fundamental physics and uncovering potential pathways to physics beyond the Standard Model.

physics.atom-ph↗
arXiv2024

Development of a real-time beam profile monitor for GeV photons and its application in accelerator facilities

A real-time beam profile monitoring system is proposed for GeV photon beams at the BM4 beamline of the Mikamine site, Research Center for Accelerator and Radioisotope Science (RARiS; previously known as ELPH) at Tohoku University. This monitoring system enhances the capability to monitor the entire beamline by incorporating newly developed beam profile monitors (BPMs) for upstream and midstream sections, in addition to the existing high-speed BPM used for downstream monitoring. This paper reports on the detection mechanisms of the newly developed BPMs and the actual measurement results obtained using the integrated beam monitoring system. The new BPMs are composed of plastic scintillation fibers and silicon photomultipliers, enabling high-precision, real-time measurements. Data acquisition utilizes streaming TDC, a firmware commonly employed in the J-PARC Hadron-hall, allowing real-time detection of high-intensity photon beams with count rates reaching several tens of MHz. With sufficient statistical data, the BPM achieved a 1-s beam-profiling accuracy of 10 μm. The proposed BPM system serves as a valuable resource for future physics experiments at the BM4 photon beamline and will significantly contribute to ongoing accelerator research endeavors.

physics.ins-det↗
arXiv2024

Feasibility of the observation of $\eta^{\prime}$ 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 $\eta^\prime$ mesic nuclei using the microscopic transport model JAM. The semi-exclusive measurements of the ($p,d$) reaction with protons from $\eta^\prime$ absorption are found to be significant for the observation of the $\eta^\prime$ bound states. Especially, the measurements of the energetic protons from $\eta^\prime$ non-mesic two-body absorption ($\eta^\prime NN \to NN$) 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 $\eta^\prime \otimes {}^{11}$C system in the semi-exclusive measurement. The semi-exclusive measurements are shown to be important in general for the $\eta^\prime$ mesic nucleus observation.

nucl-th↗
arXiv2023

Search for particle-stable tetraneutrons in thermal fission of $^{235}$U

Background: The existence of a tetraneutron comprising four neutrons has long been debated. Purpose: Motivated by a recent observation of particle-stable tetraneutrons, we investigated potential particle-stable tetraneutron emission in thermal neutron-induced $^{235}$U fission using a nuclear research reactor. Methods: We performed $γ$-ray spectroscopy for a $^{88}$SrCO$_3$ sample irradiated in a reactor core. Stable $^{88}$Sr was expected to produce $^{91}$Sr by a tetraneutron-induced ($^4n$,n) reaction; hence, observation of $γ$-rays followed by $β$ decay of $^{91}$Sr would indicate particle-stable tetraneutron emission. Results: The $γ$-ray spectrum of an irradiated $^{88}$SrCO$_3$ sample did not show any photopeak for $^{91}$Sr. Conclusion: The emission rate of particle-stable tetraneutrons, if they exist, is estimated to be lower than $8\times 10^{-7}$ per fission at the 95% confidence level, assuming the cross-sections of reactions induced by hypothetical particle-stable tetraneutrons.

nucl-ex↗
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.

nucl-ex↗
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.

nucl-ex↗
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.

nucl-th↗
arXiv2021

Feasibility of an experimental search for a resonance of a pion and a light nucleus

A hypothesis is proposed herein, suggesting that a pion-nuclear resonance may be observed in the $α+d\to{}^6\mathrm{Li}(3.563)+π^0$ reaction. The resonance has a $πNNα$ structure, containing $αNN$ and $πNN$ subsystems. The former corresponds to the $A=6$ isotriplet ($^6\mathrm{He}_\text{g.s.}$, $^6\mathrm{Li}(3.563)$, $^6\mathrm{Be}_\text{g.s.}$), whereas the latter is a hypothetical $NN$-decoupled dibaryon. We propose an experiment to search for this resonance using the $^7\mathrm{Li}(p,d)$ reaction.

nucl-ex↗
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.

nucl-th↗
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 $^9\mathrm{Be}(π^-, π^+)^9\mathrm{He}\ (g.s.)$.

nucl-ex↗