[en] An overview of recent results from bar pp annihilation at rest obtained with the Crystal Barrel is presented. These results, which provide information on meson spectroscopy, two-body final states, and meson-decay modes, offer new insight in a number of directions; the results and their implications are discussed. 49 refs., 9 figs., 1 tab

[en] We report on a measurement of the branching ratio of the rare decay ω→ηγ relative to the well known decay ω→π⁰γ. The ω's are produced in pp(bar sign)→ηω and pp(bar sign)→π⁰ω. Eigenstate mixing and interference effects of the ω and ρ⁰ are taken into account, as well as coherent interference with the background. We find evidence for the non-resonant annihilation channel B(pp(bar sign)→ηηγ)=(3.5±1.3)x10^-5 and limit the value of B(ω→ηγ) to the range of (0.7 to 5.5)x10^-4 depending on the degree of coherence with the background. (c) 2000 The American Physical Society

[en] Measurements of two-body branching ratios for pbarp annihilations at rest in liquid and gaseous (12ρ_STP) hydrogen are reported. Channels studied are pbarp→π⁰π⁰,π⁰η, K⁰_SK⁰_L, K⁺K^-. The branching ratio for the π⁰π⁰ channel in liquid H₂ is measured to be (6.14±0.40)x10^-4. The results are compared with those from other experiments. The fraction of P-state annihilation for a range of target densities from 0.002ρ_STP to liquid H₂ is determined. Values obtained include 0.11±0.02 in liquid H₂ and 0.48±0.04 in 12ρ_STP H₂ gas

[en] We present a measurement and partial wave analysis of the final state K_LK^±π^minus-plus of bar pp annihilation at rest in liquid hydrogen. This reaction is important for the study of the bar KK decay mode of scalar resonances, in particular, the isovectors a₀(980) and a₀(1450). The determination of the a₀(1450) production also fixes the bar KK coupling of the isoscalar f₀(1500) which is discussed as a glueball. We find B(bar pp→a₀(1450)π;a₀(1450)→ bar KK)=(8.88±1.68)x10^-4 and hence B(bar pp→f₀(1500)π;f₀(1500)→ bar KK)=(4.52±0.36)x10^-4. The mass and width of a₀(1450) are m=1480±30MeV/c² and Γ=265±15MeV/c², respectively. For a₀(980) we determine the relative ratio B(bar pp→a₀π;a₀→ bar KK)/B(bar pp→a₀π;a₀→πη) =0.23±0.05 and its relative coupling, bar KK to πη, is 1.03±0.14. copyright 1998 The American Physical Society

[en] We report the first observations of Pontecorvo reactions of the type pd → Xn. We fully reconstruct the outgoing meson and, for antiprotons stopped in liquid deuterium, we measure: BR ( anti pd → π⁰n) = (7.03 ± 0.72) x 10^-6, BR ( anti pd → ηn) = (3.19 ± 0.48) x 10^-6, BR ( anti pd → ωn) = (22.8 ± 4.1) x 10^-6, BR ( anti pd → η'n) ≤ 14 x 10^-6 (at 95% confidence level). Assuming charge independence, our result for anti pd → π⁰n is compatible with measurements of the only other observed Pontecorvo reaction anti pd → π^-p. The experimental ratios between the above branching ratios are in fair agreement with both the statistical model and dynamical two-step models (assuming N N annihilation into two mesons, with subsequent absorption of one meson on the remaining nucleon). This agreement suggests that there may be appreciable rates for Pontecorvo reactions producing final state mesons with masses above 1 GeV. (orig.)