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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.

We present a new proposal, J-PARC E90, to measure a missing-mass spectrum near the Σ N threshold for the d ( K − , π − ) reactions at 1.4 GeV/ c . While many previous experiments support apparent enhancement near the ΣN thresh-old, the dynamical origin of this so-called “Σ N cusp” remains yet unsolved. The enhancement suggests either a cusp structure or a weakly bound state. One of the keys to making it clear is improving the missing-mass resolution and statistics. Our new experiment can achieve the missing-mass resolution of 0.4 MeV in σ using the K1.8 beam line and S-2S spectrometers at J-PARC. Further-more, we can suppress quasi-free background processes with the time projection chamber (HypTPC), which operated nicely for the H-dibaryon search experi-ment (J-PARC E42). The J-PARC E90 aims to extract the scattering length of the Σ N system with isospin T = 1/2 and spin-triplet channels.

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 3 S 1 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 3 S 1 channel in the Σ + p channel is moderately repulsive, as the Nijmegen extended-soft-core models predicted.

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.

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.

Abstract A development has been achieved in the identification method of the charges 1 to 5 of nuclides from the decay of double hypernuclei to be uniquely recognized by their nuclear species. The method is basically the measurement of track volume by the widths, depths, and angles of tracks of exposed nuclei of $^1$H, $^4$He, $^7$Li, $^9$Be, and $^{11} $B in nuclear emulsion at RIken Projectile-fragment Separator of RIKEN Radioactive Isotope Beam Factory. After their calibration by $\\alpha$ particles, we obtained a quadric function to present a unified recognition of tracks with volume ratios of five nuclei to the $\\alpha$ particles. The function in the emulsion has been applied to a candidate event of a $\\Xi$ hypernucleus for identification of the production and decay processes. We succeeded in recognizing a daughter nuclear fragment of a single-$\\Lambda$ hypernucleus as $^6$He with a likelihood ratio of 0.9; the process was then uniquely identified as $\\Xi^-$ + $^{14}$N $\\rightarrow$${_\\Lambda}^9$Be + ${_\\Lambda}^5$He + $n$.

High-resolution spectrometers for both incident beams and scattered particles have been constructed at the K1.8 beam line of the Hadron Experimental Facility at J-PARC. A point-to-point optics is realized between the entrance and exit of QQDQQ magnets for the beam spectrometer. Fine-pitch wire chamber trackers and hodoscope counters are installed in the beam spectrometer to accept a high rate beam up to 107 Hz. The superconducting kaon spectrometer for scattered particles was transferred from KEK with modifications to the cryogenic system and detectors. A missing-mass resolution of 1.9 ± 0.1 MeV/c2 (FWHM) was achieved for the Σ peaks of (π±,K+) reactions on a proton target in the first physics run of E19 in 2010.