Hideki Kohri

Evidence for a narrow S = +1 baryon resonance in photoproduction from the neutron

The gamman-->K(+)K(-)n reaction on 12C has been studied by measuring both K+ and K- at forward angles. A sharp baryon resonance peak was observed at 1.54+/-0.01 GeV/c(2) with a width smaller than 25 MeV/c(2) and a Gaussian significance of 4.6sigma. The strangeness quantum number (S) of the baryon resonance is +1. It can be interpreted as a molecular meson-baryon resonance or alternatively as an exotic five-quark state (uuddsmacr;) that decays into a K+ and a neutron. The resonance is consistent with the lowest member of an antidecuplet of baryons predicted by the chiral soliton model.

Spin-isospin Responses of ^{71}Ga for Solar Neutrinos Studied by ^{71}Ga(^{3}He,t

Abstract The charge-exchange 71Ga(3He,tγ)71Ge reaction was used to study the spin-isospin (Gamow Teller: GT) excitations relevant to the axial-vector charged-weak response for solar neutrinos. High-lying GT states in 71Ge with excitation energies up to one MeV above the neutron threshold were found to have finite γ-decay branches to low-lying states. The GT strengths for relevant states and absorption rates of solar neutrinos through the 71Ga(ν, e)71Ge and 71Ga(ν,eγ)71Ge reactions were derived.

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Abstract We have developed a new cryogenic distillation system to purify Hydrogen-Deuteride (HD) gas for polarized HD targets in LEPS experiments at SPring-8. A small amount of ortho-H 2 ( ∼ 0.01 % ) in the HD gas plays an important role in efficiently polarizing the HD target. Since there are 1–5% impurities of H 2 and D 2 in commercially available HD gases, it is necessary to purify the HD gas up to ∼ 99.99 % . The distillation system is equipped with a cryogenic distillation unit filled with many small stainless steel cells called “Heli-pack”. The distillation unit consists of a condenser part, a rectification part, and a reboiler part. The unit is kept at the temperature of 17–21xa0K. The Heli-pack has a large surface area that makes a good contact between gases and liquids. An amount of 5.2xa0mol of commercial HD gas is fed into the distillation unit. Three trials were carried out to purify the HD gas by changing temperatures (17.5xa0K and 20.5xa0K) and gas extraction speeds (1.3xa0ml/min and 5.2xa0ml/min). The extracted gas was analyzed using a gas analyzer system combining a quadrupole mass spectrometer with a gas chromatograph. One mol of HD gas with a purity better than 99.99% has been successfully obtained for the first time. The effective NTP (Number of Theoretical Plates), which is an indication of the distillation performances, is obtained to be 37.2±0.6. This value is in good agreement with a designed value of 37.9. The HD target is expected to be efficiently polarized under a well-controlled condition by adding an optimal amount of ortho-H 2 to the purified HD gas.

)^{71}Ge Reaction

Abstract A portable NMR polarimeter system has been developed to measure the polarization of a polarized Hydrogen-Deuteride (HD) target for hadron photoproduction experiments at SPring-8. The polarized HD target is produced at the Research Center for Nuclear Physics (RCNP), Osaka university and is transported to SPring-8. The HD polarization should be monitored at both places. We have constructed the portable NMR polarimeter system by replacing the devices in the conventional system with the software system with PCI eXtensions for Instrumentation (PXI). The weight of the NMR system is downsized from 80 to 7xa0kg, and the cost is reduced to 25%. We check the performance of the portable NMR polarimeter system. The signal-to-noise (S/N) ratio of the NMR signal for the portable system is about 50% of that for the conventional NMR system. This performance of the portable NMR system is proved to be compatible with the conventional NMR system for the polarization measurement.

Distillation of hydrogen isotopes for polarized HD targets

We are carrying out hadron photoproduction experiments by using polarized photon beams with energies of 1.5-2.9 GeV at SPring-8 in Japan. In 2005, we started developing a polarized HD target for future LEPS experiments using both the polarized photon beams and the polarized target. To introduce a polarized target plays an important role in upgrading the LEPS experiments to the next higher step. The measurement of double polarization asymmetries is expected to give important informations to investigate the nucleon hidden structure, hadron photoproduction dynamics, and exotic hadron property. We report on the present status of the development of the polarized HD target at RCNP. We will carry out a test experiment to confirm that the polarized HD target can be transported from Osaka university to SPring-8 without any problems in 2010. If we succeed in the test experiment, we will carry out a long experiment to take physics data in 2011-2012.

Development of portable NMR polarimeter system for polarized HD target

Abstract For a selective excitation of spin-flip strength, ( 6 Li, 6 He) reactions can be a useful tool, because: a) 6 Li and 6 He have ground-state spin and parity values J π = 1 + and 0 + , respectively; b) 6 He has no particle-stable excited state, thus effects from ejectile excitation can be avoided. The ( 6 Li, 6 He) experiments were performed at 100 MeV/nucleon, at which incident energy the reaction is expected to be single-step dominant. Through the analysis of the good-resolution ( 6 Li, 6 He) data on 13 C, 26 Mg, 27 Al and 58 Ni targets, the evidence for a proportional relationship between 0° cross sections and the corresponding Gamow-Teller transition strengths is examined. Suppression of non-spin flip excitations is discussed based on the hindrance of the excitation of the isobaric analog state.

POLARIZED HD TARGET FOR FUTURE LEPS EXPERIMENTS AT SPRING-8 IN JAPAN

A gas analyzer system has been developed to analyze Hydrogen-Deuteride (HD) gas for producing frozen-spin polarized HD targets, which are used for hadron photoproduction experiments at SPring-8. Small amounts of ortho-H2 and para-D2 gas mixtures (�0.01%) in the purified HD gas are a key to realize a frozen-spin polarized target. However, there was an intrinsic diffi culty to measure these small mixtures in the HD gas with a quadrupole mass spectrometer (QMS) because D + and [H2D] + produced from the ionization of HD molecules were misidentified as H 2 and D2 molecules, respectively, and became backgrounds for the measurement of the H2 and D2 concentrations. In addition, the ortho-H 2 and para-D2 are not distinguished from the para-H2 and ortho-D2, respectively, with the QMS. In order to obtain reliable concentrations of these gas mixtures in the HD gas, we produced a new gas analyzer system combining two independent measurements with the gas chromatography and the QMS. Helium or neon gas was used as a carrier gas for the gas chromatography which was cooled at�110 K. The para-H2, ortho-H2, HD, and D2 are separated using the retention time of the gas chromatography and the mass/charge ratio. Although the para-D2 is not separated from the ortho-D2, the total amount of the D2 is measured without the [H2D] + background. The ortho-H2 concentration is also measured separately from the D + background. It is found that the new gas analyzer system can measure small concentrations of�0.01% for the otho-H2 and D2 with good S/N ratios.

(6Li,6He) reaction at 100 MeV/nucleon as a probe of spin-excitation strengths

We have been developing a polarized HD target for particle physics at the SPring-8 under the leadership of the RCNP, Osaka University for the past 5 years. Nuclear polarizaton is created by means of the brute force method which uses a high magnetic field (~17 T) and a low temperature (~ 10 mK). As one of the promising applications of the brute force method to life sciences we started a new project, NSI (Nuclear Spin Imaging), where hyperpolarized nuclei are used for the MRI (Magnetic Resonance Imaging). The candidate nuclei with spin ½ are 3He, 13C, 15N, 19F, 29Si, and 31P, which are important elements for the composition of the biomolecules. Since the NMR signals from these isotopes are enhanced by orders of magnitudes, the spacial resolution in the imaging would be much more improved compared to the practical MRI used so far. Another advantage of hyperpolarized MRI is that the MRI is basically free from the radiation, while the problems of radiation exposure caused by the X-ray CT or PET (Positron Emission Tomography) cannot be neglected. In fact, the risk of cancer for Japanese due to the radiation exposure through these diagnoses is exceptionally high among the advanced countries. As the first step of the NSI project, we are developing a system to produce hyperpolarized 3He gas for the diagnosis of serious lung diseases, for example, COPD (Chronic Obstructive Pulmonary Disease). The system employs the same 3He/4He dilution refrigerator and superconducting solenoidal coil as those used for the polarized HD target with some modification allowing the 3He Pomeranchuk cooling and the following rapid melting of the polarized solid 3He to avoid the depolarization. In this report, the present and future steps of our project will be outlined with some latest experimental results.

HD gas analysis with Gas Chromatography and Quadrupole Mass Spectrometer

Photoproduction reactions are dominated by isospin rules. In the case of πΔ photoproduction on the proton at forward π angles, the exchange of isospin = 1 meson(π or ρ) in the t-channel is the most dominant reaction mechanism, which is considered to give a cross section ratio σ(π+Δ0)/σ(π−Δ++) of 1/3. The cross section ratio has not been measured precisely experimentally. We present preliminary results for the cross section ratio at Eγ = 1.5–3.0 GeV. Larger ratios than 1/3 measured by our experiment at LEPS/SPring-8 suggest that the dd productions are enhanced compared with the ūu productions in the photoproduction reactions on the proton.

Nuclear spin imaging with hyperpolarized nuclei created by brute force method

Some dipole resonances in 6 Li and 7 Li nuclei were investigated via the ( 7 Li, 7 Be) reaction with an incident energy of 65A MeV. Based on the observed excitation energy, width, and cross section of each resonance, the relevant resonances are inferred to be due to excitations of the α-clusters in 6 Li and 7 Li and the deuteron-cluster in 6 Li.