[en] A fresh analysis is reported of high statistics Crystal Barrel data on pp →3π⁰, ηηπ⁰, ηπ⁰ π⁰ and ηη'π⁰ at rest. This analysis is made fully consistent with CERN-Munich data on π⁺π^- →π⁺π^- up to a mass of 1900 MeV, with GAMS data on π⁺π^- →π⁰ π⁰, and with BNL and ANL data on π⁺π^-→KK, which are fitted simultaneously. There is evidence for an I = 0, J^PC = 2⁺⁺ resonance with weak (≤7%) coupling to ππ, strong coupling to both ρρ and ωω and pole position 1534 - i90 MeV. This resonance agrees qualitatively with GAMS and VES data on ππ→ωω, previously interpreted in terms of a resonance at 1590-1640 MeV. New masses and widths for (A) f₀(1370) and (B) f₀(1500), fitted to all eight data sets, are M_A = 1300 ±15 MeV, Γ_A= 230 ±15 MeV, M_B = 1500 ±8 MeV, Γ_B = 132 ±15 MeV. Branching ratios to ππ and ηη are given, and differ significantly from earlier determinations because of a new procedure. (orig.)

[en] The Crystal Barrel spectrometer used at LEAR, CERN to study the products of anti pp and anti pd annihilations is described. A 1380 element array of CsI crystals measures photons from the decay of π⁰, η, η' and ω mesons. A segmented drift chamber in a 1.5 T magnetic field is used to identify and measure charged particles. A fast on-line trigger on charged and neutral multiplicities and on the invariant mass of secondary particles is available. The performance of the detector is discussed. (orig.)

[en] The Crystal Barrel Detector has been in operation since October 1989. Results on the analysis of the annihilation of protonium at rest into three pseudoscalars is presented. The π⁰π⁰π⁰ final state confirms the existence of f₂(1520)→π⁰π⁰. In the ηη system of the π⁰ηη final state an isoscalar J^PC=0⁺⁺ resonance with a mass of 1560 MeV/c² and a width of 245 MeV/c² is observed. The identification with f₀(1590) is doubtful since the ηη' decay is not observed with the corresponding strength. Our analysis yields an upper limit for the relative branching ratio BR(f₀(1560)→ηη')/(f₀(1560)→ηη)<0.24. (orig.)

[en] Branching ratios for antiproton-proton annihilations at rest into two mesons are given. The data were obtained at LEAR by stopping antiprotons in a liquid hydrogen target. Both charged and neutral annihilation products were detected in the Crystal Barrel detector. Representative data are presented, and their bearing on the general picture of annihilation dynamics is discussed. In addition, preliminary branching ratios for two-body radiative annihilations are given. (orig.)

[en] We discuss φ production in anti pp annihilation at rest from the Asterix and Crystal Barrel experiments and compare the branching ratios to similar final states without strangeness. The ωπ⁰/φπ⁰ production ratio is unexpectedly low. In the search for new states, the φπ⁰ mass spectrum shows no evidence for a resonance in the 1450 MeV/c² mass range but the K*K⁰π⁰ Dalitz plot shows interesting structure. (orig.)

[en] We report measurements of branching ratios for production of a series of two meson final states in anti pp annihilations at rest in liquid hydrogen. We find: BR(anti pp→π⁺π^-)=(3.07±0.13).10^-3, BR(anti pp→K⁺K^-)=(0.99±0.05).10^-3, BR(anti pp→π⁰π⁰)=(6.93±0.43).10^-4, BR(anti pp→→π⁰η)=(2.12±0.12).10^-4, BR(anti pp→π⁰ω)=(5.73±0.47).10^-3, BR(anti pp→π⁰η')=(1.23±0.13).10^-4, BR(anti pp→ηη)=(1.64±0.10).10^-4, BR(anti pp→ηω)=(1.51±0.12).10^-2, BR(anti pp→ηη')=(2.16±0.25).10^-4, BR(anti pp→ωω)=(3.32±0.34).10^-2, BR(anti pp→ωη')=(0.78±0.08).10^-2. These are the first measurements of the channels ηη' and ωη' and in almost all of the other channels are more precise than previous results. We also obtain, in a more precise fashion, the following ratios of branching ratios: K⁺K^-/π⁺π^-=0.323±0.013, π⁰η'/π⁰η=0.548±0.056, ηη'/ηη=1.31±0.15, ωη'/ωη=0.515±0.040, π⁰η/π⁰π⁰=0.303±0.010, ηη/π⁰π⁰=0.232±0.011 and π⁰ω/ηω=0.377±0.012. The measurements are made for different η and η' decays, and we thus obtain Γsub(η→3π⁰)/Γ_η→γγ=0.841±0.034, and Γ_η'→γγ/Γsub(η'→π⁰π⁰η)=0.091±0.009. (orig.)

[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.)