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The Hadron Experimental Facility at the Japan Proton Accelerator Research Complex is used for various nuclear and elementary particle physics experiments that use secondary particle beams. The secondary-particle production target is a key element for the generation of particles such as kaons and pions. To increase beam power, a new target was developed and installed. The target, which is made of gold and indirectly cooled with water, was designed so that the maximum stresses do not exceed the allowable stresses determined based on the pressure vessel standard. 95 kW is considered to be the maximum power of the primary proton beam for a 5.2-s beam duration. The new target was stably operated up to a power of 65 kW. In addition, beam position estimation based on multipoint temperature measurements of the target was demonstrated.

In the K1.8 beam-line at Hadron Experimental Facility of J-PARC, a new magnetic spectrometer S-2S is being installed. S-2S was designed to achieve a high momentum resolution of Δ p / p = 6 × 10 −4 in FWHM. Several strangeness-physics programs which require the high resolution will be realized by S-2S. The present article introduces J-PARC E70 (missing-mass spectroscopy of Ξ 12 Be) and E94 (missing-mass spectroscopy of Λ 7 Li, Λ 10 B, and Λ 12 C) experiments.

At the Hadron Experimental Facility in J-PARC, we inject a 30-GeV proton beam into a gold target to produce secondary particle beams required for various particle and nuclear physics experiments. The gold target is placed in a hermetic chamber, and helium gas is circulated in the chamber to monitor the soundness of the target. The radioactivity in helium gas is continuously monitored by gamma-ray detectors such as a germanium detector and a NaI(Tl) detector. Beam operations with those target-monitoring systems were successfully performed from April to June and October to December 2015, and from May to June 2016. In this paper, the details of the helium gas circulation system and gamma-ray detectors and the analysis results of the obtained gamma-ray spectra are reported.

A brief description of the primary beam line at the hadron experimental facility at the Japan Proton Accelerator Research Complex (J-PARC) is presented. The facility has been constructed in Tokai, Japan, and the first beam was successfully introduced into the experimental hall in January 2009. The facility utilizes a high-intensity proton beam with an energy of 50 GeV and a power of 750 kW and provides various secondary beams such as pions, kaons, and antiprotons for nuclear and particle physics experiments. We have developed beam-line components with sufficient radiation hardness and heat resistance to handle the high-power proton beam.

After the radioactive material leak accident at the J-PARC hadron experimental facility on May 23, 2013, we designed a new production target, which is capable of a primary proton beam with the energy of 30 GeV and power of 50 kW. It is made of gold and cooled by water through a copper block. For the countermeasures of the recurrence of the accident, the target is enclosed by an airtight chamber and helium gas is circulated to monitor the target soundness. In this paper, technical details of the new target design are presented.

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.

A new spectrometer system has been designed and constructed at the secondary beam line K1.8BR in the hadron hall of J-PARC to investigate $\\bar {K} N$ interactions and $\\bar {K}$-nuclear bound systems. The spectrometer consists of a high precision beam line spectrometer, a liquid 3He/4He/D2 target system, a cylindrical detector system that surrounds the target to detect the decay particles from the target region, and a neutron time-of-flight counter array located ∼15 m downstream of the target position. Details of the design, construction, and performance of the detector components are described.

Three beam lines for secondary charged particles are constructed in the hadron experimental hall of J-PARC. The K1.8 beam line, which incorporates two separators, delivers clean beams of kaons up to 2 GeV/c. The K1.8BR beam line is a branch of K1.8, for low-momentum particles up to 1.2 GeV/c. The K1.1BR beam line is a shorter line designed for low-momentum kaons. Details of these beam line designs, as well as the commissioning results, are described.

A new spectrometer system was designed and constructed at the secondary beam line K1.8BR in the hadron hall of J-PARC to investigate \\( K N\\) interactions and \\( K\\)-nuclear bound systems. The spectrometer consists of a high precision beam line spectrometer, a liquid \\(^3\\)He/\\(^4\\)He/D\\(_2\\) target system, a Cylindrical Detector System that surrounds the target to detect the decay particles from the target region, and a neutron time-of-flight counter array located \\(\\)15 m downstream from the target position. Details of the design, construction, and performance of the detector components are described.