Joseph D. Parker

Photoproduction of Lambda(1405) and Sigma0(1385) on the proton at E(gamma) = 1.5-2.4-GeV

Differential cross sections for {gamma}p{yields}K{sup +}{lambda}(1405) and {gamma}p{yields}K{sup +}{sigma}{sup 0}(1385) reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of 0.8<cos({theta})<1.0 for the K{sup +} scattering angle in the center-of-mass system. This data is the first measurement of the {lambda}(1405) photoproduction cross section. The line shapes of {lambda}(1405) measured in {sigma}{sup +}{pi}{sup -} and {sigma}{sup -}{pi}{sup +} decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the {sigma}{pi} scattering amplitudes. The ratios of {lambda}(1405) production to {sigma}{sup 0}(1385) production were measured in two photon energy ranges: near the production threshold (1.5<E{sub {gamma}}<2.0 GeV) and far from it (2.0<E{sub {gamma}}<2.4 GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.

Photoproduction ofΛ(1405)andΣ0(1385)on the proton atEγ=1.5−2.4GeV

Differential cross sections for {gamma}p{yields}K{sup +}{lambda}(1405) and {gamma}p{yields}K{sup +}{sigma}{sup 0}(1385) reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of 0.8<cos({theta})<1.0 for the K{sup +} scattering angle in the center-of-mass system. This data is the first measurement of the {lambda}(1405) photoproduction cross section. The line shapes of {lambda}(1405) measured in {sigma}{sup +}{pi}{sup -} and {sigma}{sup -}{pi}{sup +} decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the {sigma}{pi} scattering amplitudes. The ratios of {lambda}(1405) production to {sigma}{sup 0}(1385) production were measured in two photon energy ranges: near the production threshold (1.5<E{sub {gamma}}<2.0 GeV) and far from it (2.0<E{sub {gamma}}<2.4 GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.

First underground results with NEWAGE-0.3a direction-sensitive dark matter detector

Abstract A direction-sensitive dark matter search experiment at Kamioka underground laboratory with the NEWAGE-0.3a detector was performed. The NEWAGE-0.3a detector is a gaseous micro-time-projection chamber filled with CF4 gas at 152 Torr. The fiducial volume and target mass are 20 × 25 × 31 cm 3 and 0.0115 kg, respectively. With an exposure of 0.524 kg days, improved spin-dependent weakly interacting massive particle (WIMP)-proton cross section limits by a direction-sensitive method were achieved including a new record of 5400 pb for 150 GeV / c 2 WIMPs. We studied the remaining background and found that ambient γ-rays contributed about one-fifth of the remaining background and radioactive contaminants inside the gas chamber contributed the rest.

Search for

A search forKpp bound state (the lightest kaonic nucleus) has been performe d using theγd → KπX reaction at Eγ=1.5-2.4 GeV at LEPS / Pring-8. The di fferential cross section of Kπ photo-production o ff deuterium has been measured for the first time in this energy region, and a bump st ructure was searched for in the inclusive missing mass spectrum. A statistically significant bump structure was no t observed in the region from 2.22 to 2.36 GeV /c2, and the upper limits of the di fferential cross section for the Kpp bound state production were determined to be 0.1 − 7μ b (95% confidence level) for a set of assumed binding energy and width values.

K^-pp

Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which are originated from incompleteness in determining the physical parameters of Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected mere

bound state via

\sim30

\gamma d \rightarrow K^+ \pi^-X

persistent sources. It is in stark contrast with

reaction at

\sim

E_\gamma=1.5-2.4

2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3-D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be indeed helpful to reduce the background under conditions similar to space. Accordingly the significance in gamma detection is improved severalfold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below

GeV

1\times10^{-12}