Beam and SKS spectrometers at the K1.8 beam line

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 ∑ peaks of (π±, K+) reactions on a proton target in the first physics run of E19 in 2010

Hypernuclear gamma-ray spectroscopy: summary and future prospect

The present status and prospects of hypernuclear γ-ray spectroscopy are summarized. In particular, 4-body hypernuclear γ-ray spectroscopy, the recent result of 4ΛHe and the future plan of 4ΛH and charge symmetry breaking in the ΛN interaction are presented. In addition, future plans to measure the Λ-spin-flip B(M1) values of 7Λ(3/2+ → 1/2+) and 12ΛC(2− → 1−) transitions are introduced. They aim to study the g-factor of Λ in the nuclear medium

Λ polarization measurement of the

We performed the J-PARC E40 experiment to measure the Σp scattering cross sections from 2018 to 2020. Together with the π−p → K+Σ− data, the π−p → K0Λ data were accumulated as a byproduct. The analysis confirmed that Λ could be identified with an S/N ratio of ∼ 2.67. The polarization of Λ(PΛ) was preliminarily derived as 1.009 ± 0.049 for the K0 angular range of 0.7 < cos θK0, CM < 0.8. It is more accurate than the past data [1]. The high polarization enables us to measure not only the differential cross section but also spin observables of the Λp scattering in the future J-PARC experiment

Development of a triple coincidence method of reaction, gamma-ray, and weak decay in the hypernuclear gamma-ray spectroscopy at J-PARC

To understand the mechanism of the charge symmetry breaking between 4ΛH and 4ΛHe, we plan to measure the gamma-transition energy of 4ΛH (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

Results of analysis of Σ

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

High resolution spectroscopy of the “Σ

We present a new proposal, J-PARC E90, to measure a missing-mass spectrum near the ΣN 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 “ΣN 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 ΣN system with isospin T = 1/2 and spin-triplet channels