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To understand the mechanism of the charge symmetry breaking between 4 Λ H and 4 Λ He, we plan to measure the gamma-transition energy of 4 Λ H (1 + → 0 + ) with a Ge detector array. For identification of the hypernucleus, we will perform triple coincidence with the reaction, γ -ray, and weak decay for the first time. We measure the pion from weak decay with a range counter. This method will enable γ -ray spectroscopy of various hyperfragments which cannot be directly produced by ( K − , π − ) or ( π + , K + ) reactions.

X-ray spectroscopy of hadronic atoms is a powerful method to study strong interaction between hadrons and nuclei. At J-PARC, we have conducted two experiments, J-PARC E07 and E03, for hadronic atoms with a doubly strange hyperon, Ξ − , aiming at the world-first detection of their X-rays. The first measurement is performed as a byproduct of J-PARC E07 experiment with the hybrid emulsion technique. The second one, J-PARC E03, is a dedicated experiment for detection of Ξ − Fe atom X rays. The preliminary results and the present status of E07 and E03 are shown in this article. Future prospects of Ξ − -atomic X-ray spectroscopy are also discussed. A new measurement has been proposed for detecting Ξ − C atom X rays, where a novel Ξ − tracking method will be applied to realize an improved signal to noise ratio.

Abstract We present a measurement of the production of $\\Xi ^-$ and $\\Lambda \\Lambda$ in the $^{12}$C$(K^-, K^+)$ reaction at an incident beam momentum of 1.8 GeV$/c$, based on high-statistics data from J-PARC E42. The cross section for the $^{12}$C$(K^-, K^+\\Xi ^-)$ reaction, compared to the inclusive $^{12}$C$(K^-, K^+)$ reaction cross section, indicates that the $\\Xi ^-$ emission probability peaks at 70% in the energy region of $E_\\Xi =100$–150 MeV above the $\\Xi ^-$ emission threshold. A classical approach using eikonal approximation shows that the total cross section for $\\Xi ^-$ inelastic scattering ranges between 42 mb and 23 mb in the $\\Xi ^-$ momentum range from 0.4 to 0.6 GeV$/c$. Furthermore, based on the relative cross section for the $^{12}$C$(K^-, K^+\\Lambda \\Lambda )$ reaction, the total cross section for $\\Xi ^-p\\rightarrow \\Lambda \\Lambda$ is estimated in the same approach to vary between 2.2 mb and 1.0 mb in the momentum range of 0.40–0.65 GeV$/c$. Specifically, a cross section of 1.0 mb in the momentum range of 0.5–0.6 GeV$/c$ imposes a constraint on the upper bound of the decay width of the $\\Xi ^-$ particle in infinite nuclear matter, revealing $\\Gamma _\\Xi < \\sim 0.6$ MeV.

We performed a measurement of the inclusive missing-mass spectrum of the $^{12}$C$(K^-, K^+)$ reaction at an incident beam momentum of 1.8 GeV/c. This measurement was carried out by using the Superconducting Kaon Spectrometer (SKS) and the K1.8 beamline spectrometer at the Hadron Experimental Facility in J-PARC. From the missing-mass of the $^{12}$C$(K^-, K^+)$ reaction, the binding energy of a $\\Xi ^-$ hyperon in a core $^{11}$B nucleus, $B_{\\Xi ^-}$, can be calculated. Our experimental setup yielded a good energy resolution of 8.2 MeV (full width at half maximum), which allowed us to observe significant enhancements in the proximity of the $^{12}_{\\Xi }$Be production threshold region. In order to extract information from the missing-mass spectrum, we employed several fitting parameters assumptions. A good agreement with the spectrum shape was obtained by adding two Gaussian functions, with the constant experimental resolution for the $\\Xi$-hypernuclear states, to the background distribution. The peak positions were obtained to be $B_{\\Xi ^-} = 8.9 \\pm 1.4$ (stat.) $^{+3.8}_{-3.1}$ (syst.) MeV and $B_{\\Xi ^-} = -2.4 \\pm 1.3$ (stat.) $^{+2.8}_{-1.2}$ (syst.) MeV. Another model assumption, one Breit–Wigner function with $B_{\\Xi ^-} = -2.7 \\pm 2.2$ (stat.) $^{+0.5}_{-0.7}$ (syst.) MeV and $\\Gamma = 4.1 \\pm 2.1$ (stat.) $^{+1.2}_{-0.7}$ (syst.) MeV, also yielded a similar $\\chi ^2$ value.

We performed a novel Σ+p scattering experiment at the J-PARC Hadron Experimental Facility. Approximately 2400 Σ+p scattering events were identified by a kinematical consistency check for the recoil proton. The differential cross sections of the Σ+p elastic scattering were derived with better precision than in previous experiments. By exploiting high-quality differential cross section data and the simple representation of Σ+p interaction in the SU(3) flavor symmetry, we performed a phase-shift analysis on hyperon-nucleon scattering data for the first time. The absolute value of the phase shift of the 3S1 channel, where a large repulsive force was predicted due to the Pauli exclusive effect between quarks, was evaluated. These results indicate that the interaction of the 3S1 channel in the Σ+p channel is moderately repulsive, as the Nijmegen extended-soft-core models predicted.

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K 0 with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K 0 + Λ +  p was estimated from the measured integral cross section of γ + d → Λ +  X . The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K 1 , as ~ −1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K + Λ.

The J-PARC Hadron Experimental Facility was constructed with an aim to explore the origin and evolution of matter in the universe through experiments with intense particle beams. In the past decade, many results from particle and nuclear physics experiments have been obtained at the present facility. To expand the physics programs to as yet unexplored regions, the extension project of the Hadron Experimental Facility has been extensively discussed. This contribution presents the physics of the extension of the Hadron Experimental Facility to resolve issues related to strangeness nuclear physics, hadron physics, and flavor physics.

Abstract We have measured, for the first time, the inclusive missing-mass spectrum of the $^{12}$C$(K^-, p)$ reaction at an incident kaon momentum of 1.8 GeV/$c$ at the J-PARC K1.8 beamline. We observed a prominent quasi-elastic peak ($K^-p \\rightarrow K^-p$) in this spectrum. In the quasi-elastic peak region, the effect of secondary interaction is apparently observed as a peak shift, and the peak exhibits a tail in the bound region. We compared the spectrum with a theoretical calculation based on the Green’s function method by assuming different values of the parameters for the $\\bar{K}$–nucleus optical potential. We found that the spectrum shape in the binding-energy region $-300 \\, \\text{MeV} < B_{K} < 40$ MeV is best reproduced with the potential depths $V_0 = -80$ MeV (real part) and $W_0 = -40$ MeV (imaginary part). On the other hand, we observed a significant event excess in the deeply bound region around $B_{K} \\sim 100$ MeV, where the major decay channel of $K^- NN \\to \\pi\\Sigma N$ is energetically closed, and the non-mesonic decay modes ($K^- NN \\to \\Lambda N$ and $\\Sigma N$) should mainly contribute. The enhancement is fitted well by a Breit–Wigner function with a kaon-binding energy of 90 MeV and width 100 MeV. A possible interpretation is a deeply bound state of a $Y^{*}$-nucleus system.

We have measured an inclusive missing-mass spectrum of the $d(\\pi ^+ , K^+ )$ reaction at a pion incident momentum of 1.69 GeV/$c$ at laboratory scattering angles between $2^\\circ$ and $16^\\circ$ with a missing-mass resolution of $2.7 \\pm 0.1$MeV/$c^{2}$ (FWHM) at the missing mass of 2.27 GeV/$c^{2}$. In this letter, we first try to understand the spectrum as a simple quasi-free picture based on several known elementary cross sections, considering the neutron/proton Fermi motion in the deuteron. While gross spectrum structures are well understood in this picture, we have observed two distinct deviations; one peculiar enhancement at 2.13 GeV/$c^{2}$ is due to the $\\Sigma N$ cusp, and the other notable feature is a shift of a broad bump structure, mainly originating from hyperon resonance productions of $\\Lambda (1405)$ and $\\Sigma (1385)^{+ /0}$, by about 22.4 $\\pm$ 0.4 (stat.) $^{+2.7}_{-1.7}$ (syst.) MeV/$c^{2}$ toward the low-mass side, which is calculated in the kinematics of a proton at rest as the target.