Search

Data of the ηπ− system were obtained in the reaction π−p → ηπ−p at 6.3 GeV/c beam momentum. About 17 k events of ηπ− were collected in the mass range 0.8 ⩽ Mηπ- ⩽ 1.8 GeV/c2 and in the range of the momentum transfer squared 0.075 ⩽ |t′| ⩽ 0.60 (GeV/c)2. A large forward-backward asymmetry was observed around 1.3 GeV/c2 in the Gottfried-Jackson frame of the ηπ− system. A partial wave analysis of the data was performed. A peak of the D+ wave attributed to a2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/c2 in the P+ wave.

A high-statistics experiment on the reaction π − p→ π + π − π 0 n at 8.06 GeV/ c has been performed using a spectrometer detecting both charged particles and gamma rays. A partial-wave analysis based on the isobar model has been carried out for π + π − π 0 data in the mass range between 0.86 and 1.50 GeV for four t ′ regions: 0.0–0.1, 0.1–0.25, 0.25–0.45 and 0.45–0.95 (GeV/ c 2 ). Two axial-vector resonances, a 1 (1260) and h 1 (1170), were observed in the analysis. The masses and widths of a 1 and h 1 were determined to be M (a 1 = 1121 ± 8 MeV, Λ (a 1 = 239± 11 MeV, M (h 1 = 1168±4 MeV and Λ (h 1 = 345±6 MeV, respectively, by fitting the Breit-Wigner formula to the partial wave amplitude. A fit including the Deck type background was also tried in each t ′ region. The results showed a small effect on these resonance parameters and were consistent with those obtained by the simple Breit-Wigner fitting.

Experimental studies on the ωπ 0 and νπ − systems in the π − p reactions have been performed at KEK. The moment analysis of the ωπ 0 system shows a clear peak of b 1 0 (1235) in the IJ pc = 11 +− wave. In the 11 −− wave, no clear peak is seen. The properties of C(1480) with 11 −− and ϱ(1450) are discussed taking into account upper limits of their cross sections. The experiment on the νπ − system was planned to search for an exotic resonance with IJ pc = 11 −+ . The data taking run was finished and an analysis is under way.

ZnSe/GaAs interface stability and its relation with the misfit-induced film degradation which occurs above a critical thickness of the ZnSe epilayer have been studied using Rutherford backscattering (RBS). The minimum backscattering yield Xmin along the 〈110〉 channeling direction increased from 6% to 12% with the increase of the ZnSe film thickness from 1800 to 3600 A, which may indicate an increase in the density of misfit dislocations above the critical thickness. Diffusion effects at the ZnSe/GaAs interface were observed for the thicker ZnSe film samples after thermal annealing at 600°C for 5 h as evidenced by the variations of the RBS random spectra. A marked contrast was observed in the lattice matched ZnSSe/GaAs system, i.e., the interface was extremely stable even after thermal annealing. This indicates the importance of the lattice matching for the thermal stability of the heterointerface.