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Toru Harada

Publications and source records attributed to Toru Harada.

14 recordsLinked to original sources
arXiv2026

Sensitivity of the $^{3,4}$He($K^-$, $\pi^0$) production ratio to the $\Lambda$ binding energy of $^3_\Lambda$H

We study the production of $^3_\Lambda$H and $^4_\Lambda$H in the $^{3,4}$He($K^-$,$\pi^0$) reactions at $p_{K^-}=1.0$~GeV/$c$ within the distorted-wave impulse approximation, using the optimal Fermi-averaged $K^-p\to\pi^0\Lambda$ amplitude. Because the $^3_\Lambda$H ground state is extremely weakly bound, the $d$--$\Lambda$ wave function becomes spatially extended. We calculate the integrated cross sections $\sigma_{\rm lab}$ and their ratio $R_{34}=\sigma_{\rm lab}(^3_\Lambda{\rm H})/\sigma_{\rm lab}(^4_\Lambda{\rm H})$ for forward angles $\theta_{\rm lab}=0^\circ$--$20^\circ$. The production strength of $^3_\Lambda$H and the ratio $R_{34}$ are strongly sensitive to the $\Lambda$ binding energy $B_\Lambda$, which is constrained to be approximately 0.05--0.15~MeV by comparison with experimental data from the J-PARC E73 experiment. This indicates that the $^3$He($K^-$,$\pi^0$) reaction provides a sensitive probe of the weak binding of $^3_\Lambda$H.

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arXiv2025

Continuum Lambda spectra for a 6Li_Lambda hypernucleus in the 6Li(K-, pi-) reaction

We theoretically investigate Lambda production via a (K-, pi-) reaction on a 6Li target, using the distorted-wave impulse approximation (DWIA) with a Fermi-averaged K-n --> pi-Lambda amplitude. We calculate Lambda production spectra using the Green's function method for a 5Li nuclear core + Lambda system, employing a Lambda folding-model potential based on the 5Li nuclear density, which is constructed from alpha-p and 3He-d cluster wave functions. The results show that the calculated spectrum, which includes Lambda bound, resonance, and continuum states, agrees well with the experimental data from the (K-, pi-) reaction at p_K- = 790 MeV/c (0 deg.), where substitutional (0p_Lambda, 0p^{-1}_n) and (0s_Lambda, 0s^{-1}_n) configurations dominate in the near-recoilless reactions. A narrow peak corresponds to a high-lying excited state with spin-parity J^P= 1+ at E_Lambda= 13.8 MeV near the 3He + d + Lambda threshold, arising from interference effects between 5Li(3/2+)x(0s1/2)_Lambda and 5Li(1/2+)x(0s1/2)_Lambda components. This study offers a valuable framework for extracting essential information on the structure and production mechanisms of hypernuclear states from experimental data.

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arXiv2022

Extended optimal Fermi averaging for near-recoilless $\Lambda$ production in the ($K^-$, $\pi^-$) reaction on nuclei

We propose to extend the optimal Fermi averaging procedure theoretically in order to calculate an in-medium $K^-n\to \pi^- \Lambda$ amplitude for the exothermic ($K^-$, $\pi^-$) reaction on nuclei in the framework of a distorted-wave impulse approximation, taking into account the local momentum transfer generated by semiclassical distorted waves for $K^-$ and $\pi^-$ mesons. Angular distributions for the $^{12}$C($K^-$, $\pi^-$)$^{12}_\Lambda$C reaction in which a momentum transfer is $q \lesssim$ 80 MeV/$c$ at $p_K=$ 800 MeV/$c$ in the $\pi^-$ forward direction, are estimated by applying the extended procedure. The result shows that the calculated angular distributions are in good agreement with those of the data, and this extension is a successful prescription making it possible to describe the reaction cross sections in near-recoilless reactions such as ($K^-$, $\pi^-$) in our framework.

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arXiv2021

Production cross sections of $^{3,4}_\Lambda$H bound states in $^{3,4}$He($K^-$, $\pi^0$) reactions at 1 GeV/$c$

We investigate theoretically productions of $^{3,4}_\Lambda$H bound states in the exothermic ($K^-$, $\pi^0$) reactions on $^{3,4}$He targets at $p_{K^-}=$ 1.0 GeV/c in a distorted-wave impulse approximation with the optimal Fermi-averaging $K^-p\to\pi^0\Lambda$ $t$ matrix. We calculate angular distributions of the laboratory differential cross sections $d\sigma/d\Omega_{\rm lab}$ and the integrated cross sections $\sigma_{\rm lab}$ for a $J^P= 0^+$ ground state and a $J^P=1^+$ excited state of $^4_\Lambda$H at $\pi^0$ forward-direction angles of $\theta_{\rm lab}=$ 0$^\circ$-20$^\circ$, and those for a $J^P= 1/2^+$ ground state of $^3_\Lambda$H. The production of a $J^P=3/2^+$ excited state of $^3_\Lambda$H as a virtual state is also evaluated. The comparison in $d\sigma/d\Omega_{\rm lab}$ and $\sigma_{\rm lab}$ between $^4_\Lambda$H and $^3_\Lambda$H provides examining the mechanism of the production and structure of $^{3,4}_\Lambda$H, as well as in the endothermic ($\pi^-$, $K^0$) reactions at $p_{\pi^-}=$ 1.05 GeV/c. This investigation confirms the feasibility of lifetime measurements of $^3_\Lambda$H at the J-PARC experiments.

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arXiv2021

$\Xi$-nucleus potential for $\Xi^-$ quasifree production in the $^9$Be($K^-$, $K^+$) reaction

We study phenomenologically a $\Xi^-$ production spectrum of the $^9$Be($K^-$, $K^+$) reaction at 1.8 GeV/$c$ within the distorted-wave impulse approximation using the optimal Fermi-averaged $K^- p \to K^+ \Xi^-$ amplitude. We attempt to clarify properties of a $\Xi$-nucleus potential for $\Xi^-$-$^8$Li, comparing the calculated spectrum with the data of the BNL-E906 experiment. The results show a weak attraction in the $\Xi$-nucleus potential for $\Xi^-$-$^8$Li, which can sufficiently explain the data in the $\Xi^-$ quasifree region. The strength of $V_0^\Xi =$ $-17 \pm 6$ MeV is favored within the Woods-Saxon potential, accompanied by the reasonable absorption of $W_0^\Xi =$ $-5$ MeV for $\Xi^-p \to \Xi^0n$, $\Lambda\Lambda$ transitions in nuclear medium. It is difficult to determine the value of $W_0^\Xi$ from the data due to the insufficient resolution of 14.7 MeV FWHM. The energy dependence of the Fermi-averaged $K^- p \to K^+ \Xi^-$ amplitude is also confirmed by this analysis, and its importance in the nuclear ($K^-$, $K^+$) reaction is emphasized.

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arXiv2020

Medium effects on $\Xi^-$ production in the nuclear ($K^-$, $K^+$) reaction

We study theoretically medium effects on $\Xi^-$ production in the ($K^-$, $K^+$) reaction, using the optimal Fermi-averaging procedure which describes the Fermi motion of a nucleon on the on-energy-shell $K^-p\to K^+\Xi^-$ reaction condition in nuclei. The result shows the strong energy and angular dependence of the in-medium $K^-p\to K^+\Xi^-$ cross section,which affects significantly the shape and magnitude of the production spectrum for $\Xi^-$ hypernuclear states in the ($K^-$, $K^+$) reaction on a nuclear target.The application to the $\Xi^-$ quasi-free production via the ($K^-$, $K^+$) reaction on a $^{12}$C target is also discussed in a Fermi gas model.

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arXiv2019

Production of a 4He_Lambda hypernucleus in the 4He(pi, K) reactions reexamined

We investigate theoretically production cross sections of the $J^\pi=$ 0$^+$ ground state of a $^4_\Lambda$He hypernucleus in the $^4$He($\pi$,~$K$) reaction with a distorted-wave impulse approximation using the optimal Fermi-averaged $\pi N\to K\Lambda$ $t$ matrix. We demonstrate the sensitivity of the production cross sections to the $\Lambda$ wavefunctions obtained from $3N$-$\Lambda$ potentials and to meson distorted waves in eikonal distortions. It is shown that the calculated laboratory cross sections of the 0$^+$ ground state in $^4_\Lambda$He amount to $d\sigma/d\Omega_{\rm lab} \simeq$ 11 $\mu$b/sr at $p_{\pi}=$ 1.05 GeV/$c$ in the $K$ forward direction because of an advantage of the use of the s-shell target nucleus such as $^4$He. The importance of the recoil effects and the energy dependence of the $\pi N\to K\Lambda$ cross sections is also discussed.

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arXiv2017

Repulsion and absorption of the $\Sigma$-nucleus potential for $\Sigma^-$-$^5$He in the $^6$Li($\pi^-$, $K^+$) reaction

We study phenomenologically inclusive spectra of the $^6$Li($\pi^-$, $K^+$) reaction at 1.2 GeV/$c$ within a distorted-wave impulse approximation with the optimal Fermi-averaging $\pi^- p \to K^+ \Sigma^-$ $t$ matrix. We attempt to clarify the property of a $\Sigma$-nucleus potential for $\Sigma^-$-$^5$He by comparing the calculated spectra with the data of the J-PARC E10 experiment. The result shows that the repulsive and absorptive components of the $\Sigma^-$-$^5$He potential provide the ability to explain the data of the continuum spectra in $\Sigma$ and $\Lambda$ regions; the strengths of $V_\Sigma \simeq$ +30 MeV and $W_\Sigma \simeq$ $-$26 MeV are favored within the Woods-Saxon potential, consistent with analyses for heavier nuclei. Effects of the size and potential range for $\Sigma^-$-$^5$He in the neutron excess of $(N-Z)/(N+Z)=$ 0.2 are also discussed.

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arXiv2016

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. $^4\mathrm{He}({\pi}^- , {\pi}^+)$, as an alternative way to populate tetraneutron. An intense ${\pi}^-$ 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 $^9\mathrm{Be}({\pi}^-, {\pi}^+)^9\mathrm{He}\ (g.s.)$.

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arXiv2012

Discrimination of $Σ$-nucleus potentials in the angular distribution of elastic scattering of $Σ^-$ hyperons from nuclei

We theoretically investigate the elastic scattering of 50-MeV $Σ^-$ hyperons from $^{28}$Si and $^{208}$Pb in order to clarify the radial distribution of $Σ$-nucleus (optical) potentials. The angular distributions of differential cross sections are calculated using several potentials that can explain experimental data of the $Σ^-$ atomic X-ray and ($π^-$, $K^+$) reaction spectra simultaneously. The magnitude and oscillation pattern of the angular distributions are understood by the use of nearside/farside decompositions of their scattering amplitudes. It is shown that the resultant angular distributions can considerably discriminate among the radial distributions of the potentials that have a repulsion inside the nuclear surface and an attraction outside the nucleus with a sizable absorption.

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arXiv2011

Energy dependence of $K^-$-"$pp$" effective potential derived from coupled-channel Green's function

We investigate the energy dependence of a single-channel effective potential between the $K^-$ and the "$pp$"-core nucleus, which can be obtained as an $K^-$-"$pp$" equivalent local potential from a coupled-channel model for $\bar{K}(NN)$-$π(ΣN)$ systems. It turns out that the imaginary part of the resultant potential near the $πΣN$ decay threshold can well approximate the phase space suppression factor of $K^-pp \to πΣN$ decay modes. The effects on the pole position of the $π(ΣN)$ state in the $πΣN$ channel are also discussed.

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arXiv2010

Production of doubly strange hypernuclei via Ξ- doorways in the 16O(K-, K+) reaction at 1.8 GeV/c

We examine theoretically production of doubly strange hypernuclei, 16 Ξ-C and 16 ΛΛC, in doublecharge exchange 16O(K-, K+) reactions using a distorted-wave impulse approximation. The inclusive K+ spectrum at the incident momentum pK- = 1.8 GeV/c and scattering angle θlab = 0^{\circ} is estimated in a one-step mechanism, K-p \to K+Ξ- via Ξ- doorways caused by a Ξ-p-ΛΛ coupling. The calculated spectrum in the Ξ- bound region indicates that the integrated cross sections are on the order of 7-12 nb/sr for significant 1- excited states with 14C(0+, 2+) \otimes sΛpΛ configurations in 16 ΛΛC via the doorway states of the spin-stretched 15N(1/2-, 3/2-) \otimes sΞ- in 16 Ξ-C due to a high momentum transfer qΞ- \approx 400 MeV/c. The Ξ- admixture probabilities of these states are on the order of 5-9%. However, populations of the 0+ ground state with 14C(0+) \otimes s2Λ and the 2+ excited state with 14C(2+) \otimes s2 Λ are very small. The sensitivity of the spectrum on the ΞN-ΛΛ coupling strength enables us to extract the nature of ΞN-ΛΛ dynamics in nuclei, and the nuclear (K-, K+) reaction can extend our knowledge of the S = -2 world.

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arXiv2009

Coulomb-assisted $\bmΣ^-$-nucleus bound states in the ($K^-$, $π^+$) reaction

We study a production of Coulomb-assisted $Σ^-$-nucleus bound states by nuclear ($K^-$, $π^+$) reactions within a distorted-wave impulse approximation, so as to examine several types of the $Σ$-nucleus potentials that are consistent with the available $Σ^-$ atomic X-ray data and nuclear ($π^-$, $K^+$) data. We theoretically demonstrate the inclusive ($K^-$, $π^+$) spectra of the $Σ^-$ unstable bound states on $^{28}$Si, $^{58}$Ni, and $^{208}$Pb targets at incident $K^-$ lab momenta $p_{K}= 400\text{--}800$ MeV/c. The results show that the near-recoilless ($K^-$, $π^+$) reaction on the $^{58}$Ni target gives a clear candidate to confirm properties of the $Σ$-nucleus potentials having a repulsion inside the nuclear surface and an attraction outside the nucleus with a sizable absorption, whereas details of the repulsion of the potential at the nuclear center cannot be determined by the inclusive spectra. This is a promising attempt to extract properties of the $Σ$-nucleus potential in the nucleus at forthcoming J-PARC experiments, as a full complement to the analyses of the $Σ^-$ atomic and ($π^-$, $K^+$) data.

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