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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., Comment: 18 pages, 6 figures

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., Comment: 22 pages, 5 figures, 4 tables

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., Comment: 20 pages, 5 figures. arXiv admin note: text overlap with arXiv:1712.02664

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., Comment: 18 pages, 5 figures

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., Comment: 26 page, 8 figures, 4 Tables

We investigate theoretically $\Lambda$ production spectra of $^3$He($\pi$, $K$) reactions at $p_\pi=$ 1.05--1.20 GeV/$c$ in the distorted-wave impulse approximation, using the continuum-discretized coupled-channel method. The production cross section of a $^3_\Lambda$H(1/2$^+$) ground state is also discussed., Comment: 8 pages, 4 figures; contribution to the Proceedings of the 8th International Conference on Quarks and Nuclear Physics (QNP2018), Tsukuba, November 13-17, 2018

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., Comment: 35 pages, 11 figures

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 $^9\mathrm{Be}({\pi}^-, {\pi}^+)^9\mathrm{He}\ (g.s.)$., Comment: 4 pages, 1 figure; proceedings of the 14th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2016), Kyoto, Japan, 25-30 July 2016