[en] A liquid argon TPC is a very useful detector for the next generation physics to search for “CP violation in lepton sector”, “nucleon decay” and “dark matter”. The hundred kton liquid argon TPC in the Okinoshima island has been proposed to perform such physics in future. To check the detector performance of liquid argon TPC, especially particle IDs, we performed test beam in October 2010 using K1.1BR beamline in J-PARC hadron hall, so called T32 test-experiment. In last T32 experiment, the prototype cryostat with size of 250 L was borrowed from MEG (Mu → E+gamma) experiment, but we had to bring it back to Europe, therefore we started to design and have produced a new cryostat for the next possible test-beam from September 2010. For the R and D on the liquid argon TPC, the good purity is indispensable, therefore the liquid circulation system and good pre-cooling system is crucial. We added the materials for those R and D improvements to the new cryostat. We report the results of the various performance tests on the cryostat which has been performed at present in this article. (author)

[en] We are developing the high efficiently circulation system for refining liquid argon to high purity for the hundred kton liquid argon TPC. In this measurement, the liquefaction efficiency was measured with the length and the material of the heat exchanger coil. The performance of re-condenser was measured with the test bench and the prototype cryostat with size of 250 L. The efficiency of liquefaction was about 86% with the test bench. With the system of connecting of the re-condenser to the 250LAr container, the flow rate of circulating gas is the maximum 25L/min on -188.5degC of cold head temperature and the maximum 48L/min on -185.7degC. When operating by 48L/min of flow rate of supplied gas, the liquid argon of 300L was able to circulate in about 82 hours. (author)

[en] Liquid xenon has been used for dark matter searches as a sensitive scintillator that emits photons in the vacuum ultraviolet (VUV) region. In recent years, it has been reported that the xenon also emits scintillation light in the near-infrared (NIR) region. If the VUV light and the NIR light are both detected and utilized, their intensities and the time profiles might be used for additional information to improve ability of particle discrimination and energy resolution. These properties are valuable for ongoing and future dark matter searches using liquid xenon. For these reasons, we have been measuring scintillation light in the NIR region for liquid xenon and preparing new accurate experiment. We are considering two-step measurement for NIR emission; We first measure the emission wavelength accurately by long-time exposure using cooled CCD camera and a spectrometer, and then measure the emission time-profile relative to VUV emission for each NIR emission band by using cooled MPPC and bandpass filter. We did three preliminary experiments to determine whether the optical system could measure the infrared emission of liquid xenon. Firstly, we experimented whether the cooling temperature of the cooled CCD camera was low enough to distinguish between the emission spectrum and noise. The results of the tests show that the signal-to-noise ratio of the cooled camera is high enough even for long-time exposure expected for NIR light measurement of liquid xenon. Secondly, we measured the emission spectrum of NaI(Tl) scintillator, which emits photons of the same degree as liquid xenon. As a result, although the shape of the raw emission spectrum is skewed due to wavelength dependence of the optical system, the statistical error of the obtained emission spectrum is found out to be small enough, which suggests that the spectrum of liquid xenon would be measured with similar sensitivity. Finally, we measured the spectrum of the VUV light of the xenon flash lamp with quartz window. The measurement was carried out under the N₂ environment and successfully detected the characteristic emission of xenon excimer at 172 nm. As a result, a spectrum was measured in the VUV region. This result suggests that the optical system can easily measure the detailed spectrum of liquid xenon from the VUV region to the NIR region by using the appropriate diffraction grating inside the spectrometer. After determining the emission wavelength of liquid xenon NIR light, we plan to measure more detailed characteristics. The experiment of liquid xenon will start soon. (author)

[en] The emission spectrum of cryogenic liquid xenon in the vacuum ultraviolet region was measured by irradiating liquid xenon with gamma-rays from a radioactive source. To achieve a high signal-to-noise ratio, we employed coincident photon counting. Additionally, the charge of the photo-sensor signals was measured to estimate the number of detected photons accurately. In addition, proper corrections were incorporated for the wavelength; response functions of the apparatus obtained using a low-pressure mercury lamp, and photon detection efficiencies of the optical system were considered. The obtained emission spectrum is found to be in the shape of a Gaussian function, with the center at 57,199±34 (stat.)±33 (syst.) cm"−"1 (174.8±0.1 (stat.)±0.1 (syst.) nm) and the full width at half maximum of 3328±72 (stat.)±65 (syst.) cm"−"1 (10.2±0.2 (stat.)±0.2 (sys.) nm). These results are the most accurate values obtained in terms of the data acquisition method and the calibration for the experimental system and provide valuable information regarding the high-precision instruments that employ a liquid-xenon scintillator

[en] 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 10"7 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/c"2 (FWHM) was achieved for the Σ peaks of (π"±, K"+) reactions on a proton target in the first physics run of E19 in 2010. (author)